Dissertation Final

Underlying factors that affect the reflectivity of road markings
assuming the correct method of application and specification of
materials and testing has been applied
Author: Jamie B. Page
A dissertation submitted to University Campus Suffolk in part fulfilment
for
the Degree of Bachelor of Science (Honours)
Civil Engineering
Student S134992
Ipswich, Suffolk
May 2014

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The text, images and illustrations contained within this report remain the copyright of the author. No re-publication or
use of this material is permitted without the consent of the author. Works cited and used by other authors have been
referenced accordingly and their works remain the ownership of those individuals.
Word Count: 9658

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Dedication
This dissertation is dedicated to my daughter Jessica
Enjoy the gift of learning and sharing knowledge
I started this journey for myself, and finished it for you...
and to my wife, Angie
for keeping me on track over the past seven years

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Acknowledgements
To all those past teachers who have taken their time in sharing their knowledge with
me, thank you.
I would especially like to thank my Dissertation Supervisor, Andy Moss at UCS for his
guidance and continued support.
I wish to thank the staff at UK Lining Ltd for their time, support and funding for
carrying out the testing which forms part of this report and for my current and
previous employers for funding these studies.

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Underlying factors that affect the reflectivity of road markings assuming the
correct method of application and specification of materials and testing has
been applied

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ABSTRACT
This research evaluated the factors which affect the quality and performance of road
markings with emphasis on identifying how the method of installing road markings
and the choice of materials used influenced night time reflectivity. A critical review
was carried out on previous studies by others with this published literature and theory
being analysed. The report also provides an overview of the statutory duties,
economical factors, health and safety and the regulation governing the installation of
road markings within the United Kingdom.
There are two main objectives of the report:
 to determine how the timing of applying drop on glass beads after the
application of road markings affects the overall reflectivity performance
 to determine if the thickness of the road marking has an ultimate bearing on
reflectivity
Many studies have been carried out in the United States of America on the reflectivity
of road markings with glass beads applied to waterborne paint but limited studies
have been carried out for the use of drop on glass beads to thermoplastic material to
provide initial reflectivity here within the United Kingdom (UK).
Practical tests were carried out on ten 600mm longitudinal white lines with the results
being analysed in order to achieve those objectives. Thermoplastic material within
the UK is supplied with a pre mix of glass beads in granular form. A surface layer of
glass beads is added soon after the road marking has been installed to enhance its
reflectivity by reflecting light back to its original source. This report looks at the
performance of materials laid with and without the surface layer of glass beads
applied. The surface layer of glass beads is referred to as drop on glass beads
throughout this report.
The results indicated that there is a direct link between the thickness of a road
marking and the reflectivity recorded when the amount and method of applying glass
beads remained constant. The results indicated that the night time reflectivity
increased with each increase in thickness of the road marking. It was also evident

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that the timing in which the glass beads were applied had a significant effect on the
reflectivity performance. Tests suggested that reducing the time taken between
application of a road marking and drop on glass beads being applied had a positive
effect on the reflectivity recorded.
The results suggested that delaying the application of drop on glass beads by ten
seconds or more after installing the road marking, could have the same impact as not
applying drop on glass beads at all. The consequence of this is a low reflectivity
reading, a false sense of security and possible non-conformance to specification.
Given the state of road marking reflectivity on primary routes at a national level, as
reported by Road Safety Markings Association, this could be a result of not just
budget constraints but incorrect application contributing to the non conformance
across the country.

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TABLE OF CONTENTS
SUMMARY OF FIGURES 9
INTRODUCTION 11
Research Objectives 12
Scope of Study 12
LITERATURE REVIEW 13
Factors Affecting the Reflectivity of Road Markings 13
Regulation of Road Markings within the United Kingdom 16
Statutory Duties 17
Sub Contracting 18
Health and Safety at Work Act 18
Construction Design Management Regulations 18
New Roads and Street Works Act 19
Accident Data 19
Safety Schemes 20
Traffic Management Act 20
Condition of Road Markings within the United Kingdom 21
THEORY AND WRITER’S EXPERIENCES 23
METHODOLOGY 30
AGENDAS FOR TESTING 34
ANALYSIS OF THE RESULTS 38
POLISHED STONE VALUE 46
OVERALL ANALYSIS OF RESULTS 48
SUMMARY AND CONCLUSIONS 50
RECOMMENDATION FOR FURTHER STUDY AND PRACTICE 52
REFERENCES 53

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SUMMARY OF FIGURES
Figure 1. Image of 25kg bag of glass beads conforming to IS EN 1436 p.17
Figure 2(i). Diagram - light being defused p.24
Figure 2 (ii) Diagram - light being reflected p.24
Figure 3. Diagram - principles of refraction p.25
Figure 4. Diagram - bead embedment in thermoplastic p.26
Figure 5. Diagram – envelope effect p.27
Figure 6. Photograph – glass bead quality p.27
Figure 7. Diagram – embedment affected by thermoplastic temperature p.28
Figure 8. Table – specifying criteria IS EN 1436 p.30
Figure 9. Photograph – fraction particle size description on bead
packaging
p.31
Figure 10. Photograph – test markings being installed by liner’s pram p.32
Figure 11. Photograph – LTL800 Reflectometer (i) and (ii) p.33
Figure 12. Photograph – steel plate marking measuring device (i) and (ii) p.33
Figure 13. Table – testing agenda 1 – summary of results p.39
Figure 14. Graph – scatter graph showing results from testing agenda 1 p.40
Figure 16. Photograph – visual effect of beaded and non-beaded test lines p.42

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Figure 19. Table – polished stone value (skid resistance) for test lines 2, 5
and 10
p.46
Figure 20. Graph – line graph showing psv values for test lines 2, 5 and 10 p.46
Figure 21. Photograph – Standard British Pendulum test equipment p.47
Figure 22. Photograph – test line partially beaded/non-beaded p.48

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INTRODUCTION
The first road markings installed in the United Kingdom were in 1918 but it was not
until 1926 that official guidelines for their use was introduced
(Trafficsignsandmeanings.co.uk, 2014).
According to Wilson and Scott (Wilsonandscott.co.uk, 2014) during the Second World
War there were more deaths reported in London due to vehicle related accidents
during black-out periods than there were reported from enemy bombs.
There are three commonly used methods of applying road markings within the UK.
Screed applied methods, also know as manually applied, are used for all lettering,
numbering, hatching and junction markings where flexibility and movement is
required. Extruded road markings are laid by machine using a waterborne spray
paint or thermoplastic material. This method is used for greater lengths of
longitudinal road marking such as centre line and edge line. Preformed road
markings are heat transferred to the carriageway and are available in many pre
shaped designs.
Since the early introduction of road markings, the use of these has become
widespread across the world with an increasing focus on providing greater reflectivity
to aid driver safety. Glass beads are incorporated into the marking to reflect light
back in the direction it originated. This emphasis of providing a greater reflective
road marking has become more advanced and the use of glass beads for this
purpose is specified in current European Standards.
Glass beads for this purpose are known as Ballotini which was the name of the first
major company to manufacture beads for on the highway. Although other brands of
materials are now widespread, the name Ballotini has become associated with glass
beads similar to other brand names to describe a product such as Hoover, Sellotape,
Frisbee and Walkman.
The application of thermoplastic materials with glass beads is the most commonly
used product in the UK marking industry (Bridgepointroadmarkings.com, 2014).
Since the 1950s this method has been used for marking over 95% of the public roads

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in the UK and Ireland, and it is also commonly used around the globe
(Angloliners.co.uk, 2014).
Road markings recovery is considered a relativity cheap method for having an instant
visual safety impact on the road user. Under cost benefit analysis the first year rate
of return will exceed 500% and will frequently be in excess of 1,500% making road
marking improvements amongst the most effective road safety mechanisms available
to highways engineers (Comparethemarkings.co.uk, 2014).
1.1 Research Objectives
There are two main objectives of this report:
 to determine how the timing of applying drop on glass beads after the
application of road markings affects the overall reflectivity performance
 to determine if the thickness of the road marking has an ultimate bearing on
reflectivity
1.2 Scope of Study
This report is not intended to provide a comprehensive method statement of how
road markings are installed or provide a detailed analysis of different types of road
marking material and equipment used. It assumes the reader will already have a
basic understanding of road marking operations. The report aims to give the reader
a basic technical understanding behind the science of refraction and retro-reflectivity.

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LITERATURE REVIEW
Factors Affecting the Reflectivity of Road Markings
Much study has been carried out on the factors which affect the performance of road
markings with studies mostly originating from the United States of America and
Australia. Few articles have been written around the method and in particular the
timing of applying drop on glass beads to a new road marking, and how the timing in
which beads are applied to the marking affects the reflectivity performance. This
report aims to identify how the timing of applying glass beads ultimately affects the
visual impact road markings have on night time reflectivity tests. It also attempts to
provide a background of the statutory duties, regulation and performance criteria
behind applying road markings within the United Kingdom.
“Night-time visibility ... is a function of the luminous contrast between the pavement
markings and the road surface, which is generally determined by the pavement
marking retro-reflectivity (Zhang et al, 2009, p. 1). Zhang et al (2009, p.1) goes on to
suggest that using glass beads in a reflective binder, such as paint, to achieve night
time retro-reflectivity is now a worldwide accepted practice”.
The idea of applying glass beads to road marking materials to increase their
reflectivity has been about since the 1930s. A Canadian engineering journal entitled
‘Canadian Engineer’ produced an article headed up ‘Luminous Marking for
Highways’. This article first suggested the use of glass beads on the surface of
highway markings to enhance their visibility (Canadian Engineer, no date, cited at
Virginia Department of Transportation, 2012, p.2-2). Subsequently, in 1942, a further
article in ‘Popular Science’ stated that ‘marking of highway centre stripes with a light
reflecting paint is a new step forward making the roads safer at night’ (Popular
Science, 1942, cited at Virginia Department of Transportation, 2012, p. 2-2). Since
this time different highways authorities have adopted their own preference on which
type of material is used based on geographical location and cost with methods of
application and subsequent removal changing with advances in technology and
knowledge.

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There has been much study carried out by Rasdorf, Hummer and Zhang, focusing on
factors such as how the density of the beads affect reflectivity performance. Rasdorf
et al (2009, p.2) suggest that ‘traffic engineers generally believe that an optimum
occurs when 40% of each bead is exposed above the marking and 60% is embedded
in the marking’. These findings are in consideration of the glass beads applied to
waterborne paint which do not have added drop on glass to aid initial reflectivity due
to the limited thickness of this material. Similar and more relevant findings were
made by O’Brien (1989) who suggests that the optimum embedment of a glass bead
within thermoplastic is between 60-65%. This report discusses how mixing varying
sieve sizes of glass beads within a batch helps to achieve this exposure.
‘According to Rasdorf et al. (2009, p.2) bead density values have a positive
correlation with marking retro-reflectivity readings; higher bead density leads
to higher retro-reflectivity. White paint markings have significantly higher retro-
reflectivity values than do yellow markings when the bead density values are
the same’.
Their study had two main objectives. Firstly to find a way to accurately measure
bead density within a road marking and secondly to investigate the impact that bead
density had on reflectivity. Their research involved using a range of digital
processing techniques in order to visually compare images against retro-reflectivity
data (the phenonomen of retro-reflectivity is explained in the methodology section of
this report). The results suggested that visual inspection of density was hard to
conclude but results showed that reflectivity from white lines was 60% higher than
that from yellow lines. This study suggests that if white centre lines were adopted
within the USA, these would provide a 60% greater reflectivity than the current yellow
material. In practice, the cultural change will prevent such a major change from
happening. The study suggests that the UK benefits from having a centre line
system which is painted white as this could provide a significant increase in
reflectivity aiding driver safety.
However, the study suggested that the results were completed on a nominal
waterborne paint marking thickness of 15-25 mils. With a conversion rate of 0.0254

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mils to 1 mm, even at the higher end of the spectrum the thickness of the road
marking would only equate to 0.6mm, around one fifth of that laid in the UK with
thermoplastic. Therefore carrying out the same test based on UK requirements may
yield different findings altogether.
The work by Bahar et.al (2006), as reported by Zhang (2009) suggests that
thermoplastics can successfully be applied to existing thermoplastic. However,
experience has suggested that applying new thermoplastic on top of existing
thermoplastic that has not sufficiently worn can have disastrous consequences with
the new layer of material flaking and breaking away from the existing base. This can
be avoided by roughening the existing base but in practice, through experience, this
is very rarely requested by clients.
Field surveys also carried out by Rasdorf, Hummer and Zhang looked at the impact
that the direction in which beads were applied had on the performance. It was found
that when testing the double yellow centre line system (double centre line markings
are applied in a yellow colour unlike the UK where white road markings are used)
there were significant directional variations on the reflectivity test results. The study
found that there were significantly higher reflectivity readings when travelling in the
direction in which the road markings were laid than testing in the opposite direction
(Public Works Management Policy, 2009).
It may be considered that the directionality findings by Rasdorf et al and the optimum
angle of the bead gun studies by Donnel et al would go hand in hand. The beads are
being fired into the material in the direction of the moving operational vehicle. It
would make perfect sense assuming that the force of the bead fired at the material in
the direction of travel would cause the heated material to envelope around the back
of the bead blocking vision of the bead to vehicles travelling in the opposite direction.
This principle can be easily explained by placing a finger above say, an iced
doughnut. If pointing your left index finger out and inserting this into the icing,
moving in a left to right downward direction to mimic the vehicle movement and
direction of the bead fired from the gun, the tip of the finger would not be visible
looking from the opposite direction of travel. This would affect the reflectivity due to

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the material blocking any external light from entering the bead. However, tests were
carried out on aluminium test plates with data being collected in a laboratory
environment. Applying material to a test plate may distort the findings as beads
within the material may act differently than if they were applied to a negatively or
positively textured pavement surface. Further to this a portable accelerated wear
tester was used to traffic the road markings and not normal traffic loads which might
have yielded differing results.
The surface on which road markings are applied to has an overall impact on the
reflectivity of the road marking. The mean values of reflectivity measurements
collected on plant mixed pavements were found to be significantly larger than the
values collected on bituminous surface treatments (Guanghua, 2009). In the UK this
would result in areas of carriageway which have been patched or surfaced with a
micro-asphalt instead of a plant mixed hot rolled asphalt having significantly lower
readings for road markings placed on it.
Further to this, Donnell et al carried out a study to determine the optimum speed at
which a road marking vehicle should travel and also to determine the optimum angle
at which the bead dispensing gun should be aligned when firing beads at the newly
applied road marking. Their findings suggested that a vehicle travelling at 12mph
with a bead gun pointing at an angle of -20°achieved higher reflectivity.
Regulation of Road Markings within the UK
Road markings within the United Kingdom are governed by a set of European
Standards (IS EN) which specify the various levels of performance that are approved
for use in a contract specification. IS EN 1436 – ‘Road Marking Performance for
Road User’ is an end performance specification in which clients can consider the
needs of the road user allowing for them to balance the required reflectivity
performance against the required skid resistance and luminance as a higher
performance in one aspect is a loss in performance against the others (Highway
Markings Ltd, 2014).

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IS EN1436 specifies four elements of performance. These being (1) Reflection in
daylight or under street lighting, (2) Retro-reflection under vehicle headlamp
illumination, (3) Colour, (4) Skid resistance. IS EN 1423 relates to the use of drop on
glass beads (Highway Markings Ltd, 2014).
Figure 1. - (photograph: Jamie Page)
Figure 1. shows a 25kg bag of drop on glass beads which conform to IS EN 1423.
The European Standards set the specification for materials and testing. However,
the dimensions at which all road markings are placed on the highway must comply
with the Department for Transport Traffic Signs Manual - Chapter 5. This ensures
consistency across the country making the intended instruction of the road marking
easily recognisable to the end road user.
Statutory Duties
Section 41 of the Highway Act 1980 places a statutory duty on the highway authority,
which is usually the local authority, to maintain the highway and ensure safe passage
along the highway (Highways Act, 1980). Failure to maintain the highway by the
highway authority could result in legal action being taken. As was suggested by Uff.
(2009, p. 533) in the case of Gorringe v Calderdale MBC it was held that a failure of
the highway authority to maintain road markings did not constitute a failure to
maintain. It could be suggested that the outcome of this case was in part due to the
vague definition and the openness to interpretation of when maintenance, in this
case its road markings, falls below a certain standard. With regard to road markings,

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this aspect of maintenance cannot be measured in units of time as each carriageway
and each marking will be trafficked differently and will wear at various rates. IS EN
may provide a solution to this by specifying a minimum reflectivity. Information
provided by Suffolk County Council insurers suggest that records dating back to 2008
do not indicate that the network authority has been liable for lack of or poor
maintenance of road markings (Suffolk County Council, 2014).
Sub Contracting
Over ninety nine percent of the roads in England and Wales are maintainable at the
public expense (O’Flaherty 2002, p. 453). Over the past couple of decades the trend
for highway authorities has been to rapidly contract out services to the private sector
as suggested by O’Flaherty (2002, p. 453). This brings about many benefits
including passing much risk to the private sector whilst ensuring cost certainty
including the reduced costly liability of having a large pool of direct labour or items of
plant to maintain. The legal statutory requirements set out by law are not
transferable to the private sector and therefore the highway authority remain
responsible for the main contractor’s performance and approach to ensure works are
carried out as specified.
Health and Safety at Work Act
The highway authority and main contractor have responsibilities under The Health
and Safety at Work Act to ensure they provide a safe working environment for their
employees (Health and Safety Act 1974). From experience of working within the
industry, these regulations have a major impact on how works in the construction
industry are planned for and carried out.
Construction Design Management Regulations
The Construction, Design and Management Regulations place well defined
responsibilities on the client, designers and main contractors to ensure works are

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carried out safely and that all known risk is made available before works commence
(Construction, Design Management Regulations, 1996). These regulations put a
great deal of emphasis on ensuring that the contractor has all the required
information in a timely manner to ensure that works can be programmed and risk can
be made known and managed long before the commencement of works. The
regulations promote early contractor liaison for this reason and failure by any party to
carry out their responsibilities could lead to fines and imprisonment.
New Roads and Street Works Act
The New Roads and Street Works Act places a minimum training criteria on
operatives working on the highway which ensures that works are being carried out in
a safe manner and in accordance with the client specifications (New Roads and
Street Works Act, 1991).
Accident Data
Since 2005 accident data has been collected at the scene by police officers which
categorises the cause of the road accident. This data is collected nationally as part
of the STATS19 data system (Department for Transport, 2013). Data provided by
the Department for Transport (DfT) suggests that in 2011 inadequate road markings
and signs contributed to 521 accidents reported with forty eight of these being of a
serious nature and three leading to a fatality. This was from a total number of
reported accidents where police attended, of over one hundred and eighteen
thousand. This measurement is very subjective and is based upon the observations
of the police officer at the time of the reported accident. The figure would not include
all unreported accidents or near misses and the figures may also be misrepresented
as it may well be all too easy to blame the lack of or poor road markings rather than
carelessness or the driver admitting to offences such as speeding or use of a mobile
phone whilst driving. To put these figures into context the same data suggests that
defective brakes contributed to seven hundred and twenty eight accidents while
illegal or under inflated tyres attributed to seven hundred and nine accidents. Road

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markings which were visible but disobeyed, such as stop and give way lines,
contributed to over four thousand of those reported accidents in 2011 which suggests
driving behaviour rather than road marking maintenance was to blame.
It is reported that each fatality on UK roads cost the local economy £1.8m (APSE,
2012). This cost may be made up of traffic delays preventing individuals getting to
work or running a business as well as delays in delivery of goods and services. ‘Well
maintained roads support national and local economies by ensuring that freight and
business can move efficiently and safely’ (O’Flaherty, 2002, p. 452).
Safety Schemes
The introduction of safety schemes are unfortunately often the result of either a
single or multiple accidents at a particular location. Funding for road safety
campaigns has been cut by eighty percent from 2008/9 to 2011/12 down from £19m
to £4m (APSE, 2012).
The Confederation of British Industry (CBI) has estimated that congestion
costs the economy £15 billion per year, or in excess of £10 a week for every
household. As road works are clearly an impact element in this cost, the CBI
considered that their effect was a major problem and pointed to the need for
innovation and imagination in the planning, design and management of all
maintenance works to reduce this cost to the economy as far as possible
(O’Flaherty, 2002, p. 454).
Traffic Management Act
It was soon after this estimation that the Traffic Management Act (TMA) was passed
in 2004. The TMA Act requires most maintenance works which are carried out on the
highway to be noticed and road ‘space’ to be booked by the contractor or
organisation completing the works. A notice would provide the Network Inspector
and others to see from a central location who is working on each section of highway,
the nature of works being carried out and the duration that the works are planned.

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Each highway authority network is managed by a Network Inspector whose role it is
to issue and enforce penalty notices for works being undertaken without the correct
notice being in place. This Act is designed to co-ordinate highway works including
those works carried out by utility companies to prevent unnecessary delays for the
travelling public by reducing the number of traffic management set-ups on the
highway. In practice, although this may have some effect, shared road space is often
impractical due to conflicts of traffic management requirements, processes or
incompatible methods of working. The result is works still having to be carried out on
a different date. It does however ensure that unmanned traffic lights or redundant
traffic signage is not left on the highway for longer than necessary.
Roads which are funded by the public within the UK fall under two ownership
categories. Trunk roads which are primary strategic routes and include most
motorways are the responsibility of the Highways Agency to maintain. The majority
of other roads fall under the jurisdiction of Local Governments. The remainder
remain privately owned. The quality of road markings are generally measured on
retro reflectivity with an industry standard being 150mcd (APSE, 2012). The
Highways Agency specifies under TD26 that road markings which fall below a
reading of 100mcd should be surveyed for maintenance and placed on a
maintenance programme of works for their renewal with those that fall under 80mcd
being replaced immediately (DfT, 2014).
Condition of Road Markings within the UK
The Road Safety Markings Association (RSMA), which has a national membership of
over ninety road marking contractors (RSMA, 2014), carried out a survey in 2012
(carried out between July and September) to include six thousand miles of
carriageway in England, Scotland and Wales. This survey was presented to central
Government and suggested funding should be provided to highway authorities to
maintain road markings to seventy percent condition (APSE, 2012).

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The survey suggested that twenty two percent of single carriageway lines in England
alone were in critical need of replacement while twenty five percent of road markings
on dual carriageways fell below 80mcd.
Although the report suggests that the decline in performance is due to lack of
expenditure, it remains slightly biased in that it is representing its members who are
predominantly road marking contractors. The report fails to address the
consequences of poor workmanship where road marking contractors have failed to
meet client specification in terms of applying enough material when installing road
markings in order to cut costs. This could also ensure that road markings will require
renewal much sooner. Cuts in client supervision and testing programmes will
inevitably lead to failure to identify such quality issues.
The report could also be misleading as the performance measurement was a one-off
reading and not based on a number of readings to record the deterioration patterns
on the same sections of carriageway. As suggested by O’Flaherty, it is vital to know
the condition of the asset and just as importantly, changes in condition over time
(O’Flaherty 2002, p.456).
‘road maintenance is a fundamental necessity, as important as the original
road provision. The maintenance of the roadway asset must, additionally be
planned, designed and carried out in the knowledge that the road is there to
provide a high level of service to users’ (O’Flaherty, 2002, p.452).

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THEORY AND WRITER’S EXPERIENCES
This section of the report aims to discuss the theory behind the application and the
use of glass beads when used to increase reflectivity of road markings. The theory
behind what we think does happen to glass beads and how performance is affected if
the correct processes are used will be used to establish the two objectives of this
report.
Firstly it is worth pointing out that much of the study around this subject has been
carried out in the United States of America and Australia where waterborne paint is
the main road marking material used. As cited by Zhang 2009 more than 80% of
total marking mileage uses paint pavement markings (North Carolina Department of
Transport, 2008). Waterborne paint is used in the UK as a method of refreshing
existing lines where thermoplastic has been used as a base. The reasons for the
use of waterborne over thermoplastic could be for economic reasons especially
considering the vast distances which the highways cover in those countries
compared to the UK. Statistics from the DfT (2012) suggest that in the UK the total
length of the highway was two hundred and forty five thousand miles while in the
USA it is reported that the total road length is a staggering four million miles in length
as reported in the published list of countries by road network size (Wikipedia, 2014).
The statistics suggested the UK was at seventeenth position within that list.
Glass beads on the surface of a road marking are intended to reflect light when a
light source is directed towards it. When a material is normally reflective, this will
cause it to reflect light in all available directions once a light source is directed at it.
In terms of a vehicle driver requiring reflectivity of the road marking, it is of no use the
road marking reflecting and losing light in all directions as the driver remains in the
same position at a slightly different angle to the source of the light which is the
vehicles head lights. The shape and the nature of the glass beads produce what is
known as the co-efficient of retro-reflected luminance (RL), referred to throughout this
report as retro-reflectivity. This is the term which is used when light is reflected only
in the direction of the original light source. In practice, for our driver, this means that
a greater degree of light reflected from the glass bead within the road marking is
directed back towards the vehicle making the road marking more visible at night time.

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A good understanding of the phenomenon of refraction is provided by the Virginia
Department for Transportation in which the author of this report has read, understood
and provided an explanation of his understanding.
This concept of refraction is clearing visible from the illustration below.
Figure 2(i), Figure 2(ii). Copyright: Jamie Page
Figure 2(i). shows how light is diffused and lost upon impact of a surface. On impact of the surface, the light is
rebounded in all directions and little is directed back to the original source of the light (images of vehicles courtesy of
Microsoft).
Figure 2(ii). shows how the use and makeup of glass beads retro-reflect light with a good percentage of the light being
retained and reflected back towards the original light source. It is widely accepted that the greater degree of light
reflecting back to the vehicle driver would make the road marking more visible leading to a reduced risk of an accident.
The glass bead produces retro-reflectivity by refracting and returning light.
Refracting is the phenomenon of light being deflected when passing through a
medium of varying density. In other words refraction is when light travels through
anything that lets light through it, like water, plastic or glass, it deflects and gets bent.
This principle can be viewed when objects appear broken or distorted when placed
inside a glass of water (such as a straw). The light is bent most on the edges when
one medium meets another (Virginia Department of Transport, 2008). In the case of
glass beads this would be when air meets the glass.
When the light passes through a glass bead, this is deflected, or bent, in a downward
direction until it hits an obstacle and reflects backwards. The obstacle in this case
would be the thermoplastic if the glass bead were embedded into this as shown
below in Figure 3.

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Figure 3.
Figure 3. shows how light is refracted as it travels through the glass bead and deflects in a downward position. Once
this hits the solid obstacle of the thermoplastic this light is then rebounded and retro-reflected back in the direction of
the original light source (Virginia.org 2009).
A part of this report and the testing criteria is to determine what happens if a road
marking is too heavily beaded. How is the quality of light returned affected? If the
original light source travels through a number of beads, does this have the same
effect as travelling through a single bead before finally hitting the thermoplastic or
does the light get lost and bounce around between the surface areas of the beads?
This is looked at further in the testing data later in the report.
Glass beads contained within the material respond to gravitational effects which pull
the beads downwards once the material is in liquid form. Once the thermoplastic has
hardened, the beads which have ‘sunk’ into the thermoplastic have little or no effect
on the reflectivity they produce. The effectiveness of beads mixed within the
thermoplastic is only apparent once the road marking has worn to a level at which the
beads have settled. Road markings are only worn once these are trafficked by
moving vehicles. Once the top layer of a road marking has worn, the beads start to
show and reflect light back towards the light source. The more density the bead has,
the further the bead will drop into the material. This is also aided by the temperature
of the material once it is laid. Gravity will have more of an effect on a dense glass
bead in very hot material than it will with a less dense bead in material being laid at a
reduced temperature.
Copyright: Jamie Page

[26]
Other factors will also have a direct impact on the level at which the bead settles
such as temperature at ground level. On a cold winter’s day, thermoplastic will
harden much quicker than say in mid-summer when heat is the cause for some
surfaces with a high bitumen content to breakup. In the latter scenario, the heat will
aid the thermoplastic to stay in a viscous state for longer aiding the gravitation effect.
While on a cold day the reduced hardening time of the thermoplastic will cause each
bead to settle nearer the surface of the line. It would be unrealistic and not possible
to continually change the laying temperature of the thermoplastic to counteract these
variants which may change on an hourly basis or by localised weather conditions. In
practice, this issue is overcome by the glass beads within a batch being a mixture of
various grades and sizes so these settle at varying levels within the road marking
which then aids the continued reflectivity during the majority of the lifetime of the road
marking. The optimum bead density on the surface of road markings according to
O’Brien (1989) is between 60-65%. Beads less well embedded may be plucked from
the surface while beads which have a too great an embedment may not allow
sufficient light to pass through returning less light.
Figure 4.
Figure 4. shows in diagrammatic form how a variation in the grade of the glass beads allows embedment within the
thermoplastic so that ground temperature conditions are counteracted and that there is little requirement for the
temperature of the material to be adjusted prior to installation of the road marking. Beads which do not embed well
within the material may be plucked out by oncoming traffic and have its longevity reduced. This could have major
consequences in the quality and performance of the road markings if numerous beads sever from the plucking effect.

[27]
Gravitational effects aid each bead to become embedded within the thermoplastic
while is it is in a molten state. Once the beads are dropped onto the newly laid road
marking, the weight of the bead causes this load to act downwards. The subsequent
action for the hot thermoplastic material which surrounds the bead is to ‘envelope’
around the beads’ sides as the thermoplastic is being pushed out of place by the
gravitation and applied forces. As the thermoplastic material has nowhere else to go,
this surrounds the glass bead in an upwards direction as shown in figure 5 below.
Figure 5.
Figure 5. shows how the gravity forces beads to embed within the thermoplastic forcing the excess thermoplastic to
envelope around the edges of the bead resulting in further embedment.
Figure 6(i). standard glass bead mix. Figure 6(ii). high quality glass bead mix being more rounded
(Photographs: Jamie Page)
Material envelopes
embedding glass bead

[28]
The quality of light returned by glass beads is measured by a Refraction Index (RI)
number. As the night time reflectivity test is the most common road marking testing
procedure, the RI number and visual appearance of the road marking will ultimately
be used to determine the quality of the road marking. The chemical elements and
the nature of the glass bead such as its size and roundness will determine the RI
number. Higher quality beads can cost as much as three times that of the standard
used on much of the UK network. Higher quality beads can be specified for accident
black spots particularly those linked to wet night incidents or where a very high
quality of road markings is require such as a runway. Most clients specify a minimum
RI of RI1.5 (Class A) to meet requirements of EN:1423 (1997) with a much higher
quality of glass bead having an RI of RI1.9.
Much work has been carried out in the United States of America on this subject and it
is suggested that there is direct link between bead density and reflectivity
performance. Furthermore, bead density values have a positive correlation with
marking retro reflectivity readings; higher bead density leads to higher retro
reflectivity (G Zhang et al: 2009)
Figure 7(i), (ii) and (iii)
Figure 7. shows how the temperature of the thermoplastic material would impact on the bead density at the surface of
the marking. Figure (i) shows how a bead would embed if the material was very hot. There is no bead density on the
surface of the line as this has been allowed to sink into the material due to material heat and weight of bead. Figure (iii)
shows how the bead would embed if the material was cooler or if there was a delay in applying beads. This would
cause the bead to have too great a density at the surface and cause this to be plucked from the material. It is
suggested by Zhang (2009) that a bead density of 60% would be optimal as shown in the Figure (ii).
The temperature of the thermoplastic material affects the positioning of glass beads
dropped on the surface. Thermoplastic which is too hot will allow the beads to travel
down through the material causing the beads to become enveloped and covered not
allowing these beads to give initial reflectivity as shown in the first illustration. Beads
applied at the optimum time will allow a percentage of these beads to embed
allowing for the correct density of the bead to sit on the surface of the material as

[29]
shown in the second illustration. When material has been allowed to cool before
beads are applied, a skin will form on top of the cooling plastic which will prevent the
beads from becoming suitably embedded within the material. This will cause excess
beads to be blown away or plucked from the surface.
Glass beads are generally environmentally friendly as these are made out of recycled
glass. However, the application of glass beads in an environmentally sensitive area,
such as over a water course, may require liaison with such bodies as the
Environmental Agency. The use of drop on glass beads where an element of these
are blown off the marking, or plucked out over time, could cause pollution.

[30]
METHODOLOGY
There were two main objectives for this report to establish:
 how the timing of applying drop on glass beads after the application of road
marking affects the overall reflectivity of the road markings
 how the thickness of the road marking affects its reflectivity
Other studies have very much focussed on factors affecting reflectivity which include
glass bead roundness and clarity, direction of travel, embedment and bead density.
Much of this study has been carried out for operations using waterborne paint laid by
an extrusion machine where beads are shot at the new road marking by an air
powered gun attached to the vehicle. Therefore beads of this nature are almost
immediately applied to the new line as the vehicle is passing the newly installed line.
Little study has actually been carried out to determine how delaying the application of
glass beads affects a line’s reflectivity. Another reason for this is that from the
literature studied, screed operations are a lot more common in the UK than in the
USA where much study has taken place. Screed method of applying road markings
is required for painting markings such as lettering, directional arrows, junction
markings and shorter lengths of longitudinal markings. With all screed works the
timing of applying glass beads are not as instantaneous and are dependent on the
organisation and knowledge of the operatives.
It must be made clear that this report is focussed entirely on the testing and
subsequent changes to the reflectivity based on the application of drop on glass
beads and not the content of glass beads mixed as standard in each batch of road
marking material. Drop on glass beads are used to provide initial reflectivity to road
markings.
Figure 8.

[31]
Figure 8. shows an extract from IS EN 1436 specifying criteria an end performance measurement which allows clients
to specify their end performance requirements.
It was identified that to adequately achieve the objectives of this report a number of
practical tests would be required and results analysed with visual accounts assessed.
The tests would identify the night time reflectivity (RL) measured in millicandelas per
square meter per lux which is represented by the equation of mcd/m²/lux.
Each test was carried out by a qualified and competent road marking crew with over
fifty five years amalgamated experience of road marking operations. Thermoplastic
material made from polymer resin was used with the material being heated to
approximately 180°.
Glass beads used for tests carried out as part of this report were Class A with a
Refractive Index of 1.5 (RI1.5)with a mixed diameter ranging from 850 Microns which
measures .0334 inches (U.S Sieve size 20) to 125 Microns measuring less than
.0050 inches (U.S Sieve size <80). At this range the beads are considered typical
standard beads and not large beads.
Figure 9. shows the fraction diameter range for glass beads used. In this case a diameter of between 850 and 125
microns were used which are classed as a typical standard bead.
It was anticipated that the tests would be carried out with white thermoplastic test
lines being laid on an outdoor asphalt surface to mimic environmental conditions

[32]
found on site. However, due to persistent heavy showers, tests were carried out on a
concrete surface under cover within the compound of a storage facility. Laying
thermoplastic on a concrete surface in an outdoor location would require three
consecutive dry days to ensure the bond between the surface and the thermoplastic.
A tack coat would be applied to the surface, usually applied with a roller. The tack
coat is a requirement for concrete surfaces when thermoplastic is being applied as
this acts as glue and reduces the chance of thermoplastic flaking and ultimately
failing to bond. For test purposes, tack coat was not applied to the concrete before
the application of thermoplastic as the markings were not required as a permanent
measure. In the author’s view these variations would have had little impact on the
test results themselves and there was no reason to suggest that these would have
had severe consequences to the results recorded.
Figure 10. shows the road markings being installed using a liner’s pram. The gas bottle on the rear of the pram
provides a naked flame which continuously keeps the material held within the pram hot to prevent this from curing
prematurely.
Testing was carried out using a LTL800 mobile Retrometer which had been
calibrated three weeks before the date of the testing.

[33]
Figure 11(i) and (ii) - (photographs: Jamie Page)
Figures 11(i) and (ii). A handheld portable Retrometer LTL800 was used for testing.
Ten test lines measuring 600mm in length were laid in total. The thickness of each
line was measured with a moulded steel plate to ensure that the correct amount of
thermoplastic had been applied.
Figure 12(i). Figure 12(ii). - (photographs: Jamie Page)
Figure 12(i). shows a moulded steel plate used to measure thickness of line. The plate is approved by BSI (British
Standards Institution). Figure 12(ii). shows the depth of the plate cut in mm (2mm).

[34]
AGENDAS FOR TESTS
Ten 600mm white thermoplastic test lines were divided up into four different testing
agendas as follows:
TESTING AGENDA 1 (TEST LINES 1/2/3)
To identify how the thickness of a road marking affected it’s reflectivity without the
application of drop on glass beads.
To identify how the thickness of a road marking affected it’s reflectivity with the
application of drop on glass beads applied to the surface of the thermoplastic. Each
of the test lines 4, 5 and 6 has an identical quantity of drop on glass beads applied
immediately (up to three seconds) after the thermoplastic was laid.
To identify how the speed in which drop on glass beads were applied to a road
markings affected it’s reflectivity. Each of the TEST LINES 7, 8 AND 9 had an
identical quantity of drop on glass beads applied at varying times after the
thermoplastic line had been laid.
TESTING AGENDA 4 (TEST LINE 10)
To identify how the application of a heavily beaded line affected it’s reflectivity. TEST
LINE 10 had a greatly increased application of drop on glass beads to cover the vast
majority of the surface of the thermoplastic. The beads were applied immediately
after (up to three seconds after) the line had been laid.
Each of the test lines which had drop on glass beads applied was lightly swept with a
soft bristled brush after the road marking had hardened. This was to remove excess
glass beads and this process would have occurred naturally on site through
atmospheric conditions and passing road traffic.
Each of the ten 600mm test lines were laid manually by a road marking pram. All
drop on glass beads were applied directly from beads loaded into a bead dispenser
connected to the road marking pram. The beads are released by a trigger action

[35]
operated by the white liner in similar fashion to the operation of a bicycle brake. The
bead dispenser releases a continuous, steady flow of beads which covers the width
of the road marking being laid.
Test Line Specification and Prediction
The specification for each of the ten test lines were as follows with a prediction of
what I would have expected the results to show.
Testing Agenda 1
TEST LINE 1 - 1mm thin line no drop on glass beads
TEST LINE 2 - 2-3mm normal line no drop on glass beads
TEST LINE 3 - 3-5mm thick line no drop on glass beads
With the theory described above noted, I would expect the TEST LINES 1, 2 and 3
would produce low reflectivity as there are no drop on glass beads applied. These
lines would have not have been trafficked to expose the beads held within the
material. I would expect these lines to fall well below the 150 mcd industry standard
and would also expect these to fall around or below the 100mcd limit as specified in
the data sheet for the material provided due to the lack of wear and exposure of the
beads.
I would predict that the increase in thickness of the road marking will have a positive
impact on the reflectivity although I would expect that the overall reflectivity to fall
short of the required standard. This is due to the beads within the material being
enveloped by the thermoplastic blocking exposure to the surface of the line. TEST
LINE 3, which has a thickness of up to three times that of TEST LINE 1, may still not
have the top layer of beads exposed as the thickness of the line would not change
the gravitation effect applied on the glass beads.
Testing Agenda 2
TEST LINE 4 - 1mm thin line with drop on glass beads applied
TEST LINE 5 - 2-3mm normal line with drop on glass beads applied

[36]
TEST LINE 6 - 3-5mm thick line with drop on glass beads applied
With the addition of drop on glass beads being added to the installed test lines, I
would expect the results to vastly improve upon those test lines from Testing Agenda
1. I would predict that there may be a small increase in reflectivity readings with
each increase in thickness of line or for the readings to remain at a constant level
due to approximately the same drop on glass bead area coverage across all three
lines.
Testing Agenda 3
TEST LINE 7 - 2-3mm normal line drop on beads applied after 30 seconds
TEST LINE 8 - 2-3mm normal line drop on beads applied after 10 seconds
TEST LINE 9 - 2-3mm normal line drop on beads applied less than 3 seconds
The testing of road markings where drop on glass beads have been applied at
varying durations was carried out in order to see what the impact of delay would have
to the immediate reflectivity of the road marking. These tests would in effect mimic
the impact and the reality of road markings operators becoming distracted or simply
not being aware of the relationship between when the road marking has been laid to
when the drop on glass beads are applied. In practice, the timing of application of
drop on glass beads if applied would depend on resource, tools and organisation of
the road operatives.
With experience of knowing how the thermoplastic hardens after installation, I would
predict that beads laid after 30 seconds of the lines being applied may not fully
embed into the material as this would have almost certainly fully cured, especially on
a day where temperatures are low such as the case of the day of testing. I would
predict that while applying beads up to 10 seconds after the lines have been installed
most of the beads would suitably embed within the material therefore giving a
reflectivity reading which would probably comfortably pass the quality requirements.
For the lines in which beads are added within 3 seconds of the road marking being
applied, I would predict that although some beads may become enveloped by what
will be thermoplastic at very high temperatures, the embedment of most beads will

[37]
allow a sufficient density of bead to be visible at the surface to refract light to provide
a suitable returned reflectivity. I would assume that applying glass beads on lines
within 3 seconds of installation would give the most positive return of reflectivity.
Testing Agenda 4
TEST LINE 10 - 2-3mm normal line heavily applied with drop on glass beads
I would predict that in applying excessive glass beads to a line, this would not impact
significantly on results compared to a line which had glass beads applied to its
surface. There may be a slight increase in reflectivity recorded compare to say line 5
but I would not expect this recorded figure to double if the drop on glass beads were
doubled.

[38]
ANALYSIS OF THE RESULTS
The first observation of the test results was that even at the higher end of the
recorded results, the reflectivity values recorded were lower than what I would have
expected. This may be due to the tests being carried out on a concrete surface and
not a plant mixed asphalt. This would go hand in hand with the studies carried out by
Hummer et al suggesting that reflectivity for road markings on plant mixed
aggregates gave significantly better values than those on micro asphalts.

[39]
Testing agenda 1 (TEST LINES 1/2/3)
To identify how the thickness of a road marking affected it’s reflectivity without the
Summary of results
Night time reflectivity reading Average
Test 1 – 1mm thin line no additional beads
5 readings
direction 1
44 47 66 74 80 Average
reading RL
(mcd)
58
5 readings
direction 2
52 51 49 55 60
Test 2 – 2-3mm normal line no additional beads
5 readings
direction 1
50 54 55 63 56 Average
reading RL
(mcd)
57
5 readings
direction 2
60 54 71 56 51
Test 3 – 3-5mm thick line no additional beads
5 readings
direction 1
46 48 51 50 44 Average
reading RL
(mcd)
53
5 readings
direction 2
52 52 51 62 74
Figure 13.
The thickness of road marking where no drop on glass beads had been added had
no positive impact or relation to the increase of reflectivity recorded. In fact, the
greater the thickness of road marking in this case had a reverse affect on the
reflectivity result. This could be due to the greater depth of thermoplastic material in

[40]
the thicker lines being able to envelope around the beads already contained within
the material. Whereas with the thin line as in Test 1, there may not be enough depth
of material in order for the beads contained within the material to have such a
gravitational effect and due to the line being laid so thinly may be partially visible on
the surface resulting in a higher than expected reading.
Figure 14.
Figure 14. shows scatter graph of results from Testing Agenda 1 where no drop on glass beads have been applied.
The results surprisingly show a small decrease in reflectivity recorded with each increase in line thickness.

[41]
To identify how the thickness of a road marking affected it’s reflectivity with the
Summary of results
Test 4 – 1mm thin line with additional beads applied
5 readings
direction 1
112 104 101 122 106 Average
reading RL
(mcd)
94
5 readings
direction 2
73 85 79 86 72
Test 5 – 2-3mm normal line with additional beads applied
5 readings
direction 1
129 149 153 123 118 Average
reading RL
(mcd)
170
5 readings
direction 2
164 241 197 216 210
Test 6 – 3-5mm thick line with additional beads applied
5 readings
direction 1
128 160 150 155 188 Average
reading RL
(mcd)
234
5 readings
direction 2
240 462 275 418 162
Figure 15.

[42]
Figure 16. shows how reflectivity of road markings is
enhanced by the use of drop on glass beads. The image
was taken with the warehouse shutters closed to mimic
night-time hours as much as possible. The flash on the
camera could be considered to be acting as a head light.
The image shows that the first two lines have no drop on
glass beads applied against line three and four which are
returning significantly more reflectivity back to the
original light source.
Figure 16.
Test Lines 4/5/6 showed a direct relationship between the thickness of road marking
line and reflectivity recorded. The thicker the line laid the greater the reflectivity
recorded. The results showed that by applying road marking at 3mm in thickness as
standard contract requirement, this significantly increased the retro-reflectivity
recorded. The consequence of a road marking crew laying a line too thinly would not
only result in the line requiring renewal as a faster rate, but also mean that the road
markings will not perform as required in terms of reflectivity.
This represents almost a one hundred and fifty percent increase in reflectivity
recorded from applying a 1mm thick line to a 3-5mm thick line. This is directly related
to the increase in additional material which will be used.

[43]
To identify how the timing of applying drop on glass beads to a fresh road marking
affected its reflectivity
Summary of results
Test 7 – 2-3mm normal line beads applied after 30 seconds
5 readings
direction 1
64 58 48 59 53 Average
reading RL
(mcd)
56
5 readings
direction 2
54 50 59 55 62
Test 8 – 2-3mm normal line beads applied after 10 seconds
5 readings
direction 1
90 69 74 93 146 Average
reading RL
(mcd)
100
5 readings
direction 2
162 118 81 63 100
Test 9 – 2-3mm normal line beads applied less than 3
seconds
5 readings
direction 1
152 174 120 169 173 Average
reading RL
(mcd)
161
5 readings
direction 2
154 151 163 178 179
Figure 17.
Test 9 was effectively the same test as Test 5 which is shown by the results of 161
and 170 respectively being almost identical. Beads applied up to 30 seconds after
the line had been laid yielded the same results as those lines not having beads
applied at all. Delaying the application of drop on glass beads after the initial 3

[44]
seconds of the lines being installed had significant impact on the reflectivity recorded.
The results of these tests lines identified how distraction on site or cooler
temperatures could make the difference between a high reflectivity value and a low
one resulting in the difference between a road marking failing or passing its
performance requirement.

[45]
Testing agenda 4 (TEST LINE 10)
To identify if applying excess drop on glass beads had a positive or negative impact
on the reflectivity recorded
Summary of results
Test 10 2-3mm normal line heavily applied with beads
5 readings
direction 1
125 116 111 118 131 Average
reading RL
(mcd)
110
5 readings
direction 2
99 94 100 105 96
Figure 18.
If we look at how this result fared against a line of the same thickness with fewer or
no beads applied it can be identified how much of an impact that excessively beading
a line can have on its reflectivity reading. Although excessively beading a line may
be thought of as a method for an operative to ensure lines give a high reading, this
does in fact have the opposite impact. The result in this case is that the line only just
passes over the 100mcd requirement. It would not be cost sustainable excessively
beading each line nor sustainable in terms of the environmental impact that this may
have.
It can be seen that in line 2 where no drop on glass beads were applied a reading of
only 57mcd was recorded which is only half of that recorded with an over excessively
beaded line. The results recorded in line 5 suggest the reading which could have
been achieved if the line was not as heavily beaded.
In fact, over excessive bead use in this scenario had the same impact of delaying the
application of glass beads for up to 10 seconds after the initial application of road
marking as shown in line 8 where the reading recorded 100mcd. It could also be
considered that excessive use of beads would have the same impact as reducing the
thickness of line as shown in line 4.

[46]
POLISHED STONE VALUE
A Standard British Pendulum Test was used to measure the skid resistance on three
of the test lines to show how the increase in surface bead coverage had a negative
effect on the lines skid resistance. Glass beads are polished and have a lower
polished stone value than thermoplastic. Therefore it would be expected that the
greater the amount of glass beads being applied to the surface of a road marking the
lower the psv reading should be.
Rate of surface applied drop on glass beads Skid Resistance
Value
No drop on glass beads applied - (Test Line 2) 55
Glass beads applied at approximate rate of 475g per m²
thermoplastic (+/- 50g per m²) – (Test Line 5)
47
Drop on glass beads heavily applied at approximate rate of
800g per m² - (Test Line 10)
33
Figure 19.
Figure 20.
Figure 20. shows the correlation between the coverage of glass bead per m² of road marking and the decrease in skid
resistance.

[47]
In theory this means that a car will take longer to come to a stop when skidding on a
heavily beaded thermoplastic surface than on thermoplastic surface which has little
or no amount of glass beads applied.
Figure 21. - (Photograph: Jamie Page)
Figure 21. shows a Standard British Pendulum Test apparatus to measure skid resistance of a wetted line.
I would expect that we would see a reduction of the psv value as the quantity of
beads applied to the surface increases. This is backed up in findings noted by
Woodward, “based on reported research small increases for higher psv aggregates
correspond to large decreases in terms of wear and other test properties”
(Woodward, 1995). Although thermoplastic is not considered an aggregate, the
principles for this surface material remain the same.

[48]
OVERALL ANAYLSIS OF RESULTS
In general the results yielded were largely what was expected although the values
recorded for all tests were somewhat lower that initially expected based on previous
on-site experience. The values recorded for Test Lines 1/2/3 which were laid without
the application of any drop on glass beads were particularly surprising as the
reflectivity which the data sheets of the material suggest can be achieved, would only
become apparent after the initial trafficking of the road markings. There was a small
increase in results where the road marking was laid exceptionally thinly at 1mm. It
makes sense that although you expect this to be the poorest performing line it in fact
yielded higher results than Test Lines 2 and 3 which were both laid thicker. As
explained above, this could be due to the ready mix beads not having enough
material to sink into causing the beads to sit at the surface of the marking giving a
greater reading. For all lining criteria in Testing Agenda 1, it may be several weeks
or months after the road markings have been installed on the carriageway before
these are trafficked significantly to expose the ready mixed glass beads. As the
research carried out by Hummer et al suggests as detailed in the literature review,
the fact that these tests were carried out on a concrete surface rather than a plant
mixed asphalt could explain why the range of results was lower than expected.
Figure 22. – (photograph: Jamie Page)
Figure 22. shows a very clear image of how applying drop on glass beads makes a very significant impact on initial
reflectivity showing a line which has been partially beaded. Evidence that the line has had beads applied is also
shown by the excess beads that have been swept from the surface and that sit alongside the Test Line.

[49]
The results gathered suggested that the best performing line was laid at 3-5mm
where drop on glass beads were applied up to three seconds after the line was
installed. These results were so conclusive that it is felt the objectives of the testing
have been met. It had been evidenced that where drop on glass beads were used,
the thickness of the line had a direct impact on its reflectivity. It is appreciated that
different values of the readings gathered may be returned with the use of other
testing equipment or with tests being carried out on an asphalt surface. With this
said, the trend of results were so conclusive that they have identified how the timing
of applying drop on glass beads affects the overall reflectivity of a road marking.
The objective of identifying if the thickness does in fact affect its reflectivity, has, with
reasonable confidence, been met. With such an increase in the values recorded for
the varying thickness of the road marking, this would suggest the thickness in which
the road marking is laid has a direct impact on the reflectivity provided.

[50]
SUMMARY AND CONCLUSIONS
In summary reflectivity is ultimately the night time performance measurement to
determine the condition of road markings while day time performance will be
determined by reflectivity testing and visual inspection. Reflective glass beads are
used to enhance the night time visibility of road markings. In order to achieve high
reflectivity as detailed in the report, many factors will be required. In terms of
materials used specifying glass beads with a refractive index (RI) suitable for the
intended purpose and location of the road marking is critical. The higher the RI
number, which again is directly linked to the shape, size and chemical makeup of the
beads, the greater degree of retro-reflectivity that will be returned to the original light
source provided other variables have been met.
The findings from the tests results suggest that until a road marking has been
trafficked to expose the glass beads mixed within the thermoplastic, a road markings
will give off very little reflectivity unless glass beads have been applied to the top
surface of the marking. This was due to the gravitational effect forcing the bead to
act downwards being enveloped and finally covered by the thermoplastic while in a
molten state. However, it was surprising that the results for the tests without drop on
glass beads applied were so low, giving the fact that the thermoplastic data sheet
suggested that the material with mixed glass beads gave a reflectivity of 100 mcd/m²/
lux. Until such time that the road marking was suitably trafficked this would not be
achieved. Although in time these markings will perform better by providing an
increased reflective line, this is little comfort or use to the initial road users. The use
of drop of glass beads to act until the beads are exposed within the material is clearly
critical for this reason.
Results from the tests clearly showed that there is a direct comparison to the
thickness of a road marking and the overall reflectivity once drop on glass beads
were applied. Each increase in thickness resulted in a comparable increase in the
reflectivity readings taken.
The timing in which drop on glass beads were applied to a road marking had
significant impact on the performance and degree of reflectivity reading. It was clear
that the percentage of beads applied after three seconds of the road marking which

[51]
embedded within the material decreased significantly causing excess beads to sit
loosely on the surface, finally being swept or plucked away once the markings were
given a light sweep to mimic the effects of environmental and traffic conditions on
site. Applying glass beads after ten seconds of the marking being laid had the same
results as not applying a surface layer of glass beads at all. If distraction or lack of
knowledge caused beads to be delayed by this amount of time a false sense of
security and a complete waste in the cost and time of applying the beads would have
been had. The need to apply the surface layer of beads before the thermoplastic
forms a ‘skin’ as this cools is critical.
Skid resistance which is measured to determine the Polished Stone Values of a
particular material decreased as the amount of glass beads increased on the surface
of the road marking. In practice this would have little effect on the overall braking
distance of a vehicle as a typical road marking coverage as a percentage of
pavement area is relatively small. Although it is still worth designers to consider this
factor when specifying bead coverage.
A typical road network represents the largest in place asset component of the
national publicly financed transport infrastructure. It is necessary and morally correct
to manage and importantly be seen to manage the asset as efficiently and effectively
as possible (O’Flaherty, 2012. P.456).

[52]
RECOMMENDATIONS FOR FURTHER STUDIES AND PRACTICE
It is recommended that further research is carried out in the following areas:
 To study the spread rate accuracy provided by the current equipment
available to road marking crews in order to achieve a more consistent spread
of drop on glass beads.
 Improvements to the initial performance of thermoplastic material to take the
onus off the road markings crew to apply drop on glass beads within three
seconds for screed operations.
 Published league table being provided by the likes of the RSMA to give
accountability of contractor’s performance in relation to independent audits
being carried out by the professional body on its members.

[53]
REFERENCES
1. Gov.uk, (2012). Road lengths statistics in Great Britain: 2011 - Publications -
GOV.UK. [online] Available at: https://www.gov.uk/government/publications/road-
lengths-statistics-in-great-britain-2011 [Accessed 8 March. 2014].
2. Uff, J. (2009) Construction Law: Law and Practice relating to the Construction
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