The document provides a comprehensive overview of road signs, traffic signals, and road markings relevant to road safety engineering. It details the classifications, roles, and design considerations of various traffic control elements, emphasizing the importance of effective signal timing, delineators, and intersection management to enhance road safety. Additionally, it explains the distinctions between at-grade and grade-separated intersections and the factors influencing their design and implementation to reduce accidents and improve traffic flow.

1. Road Signs and Traffic
Signals
Road Safety Engineering UNIT-3

2. Contents
• Road Marking: Role of Road markings, Classification, visibility.
• Traffic Signals: Need, Signal face. Illumination and location of Signals,
Factors affecting signal design, pedestrians‘ safety, fixed and vehicle
actuated signals. Design of signals, Area Traffic control.
• Delineators, Traffic Impact Attenuators, Road side rest areas, Safety
Barriers, Traffic Aid Posts.
• Road Signs: Classification, Location of Signs, measures of sign
effectiveness, Types of visual perception, sign regulations, sign
visibility, sign variables, Text versus symbols.

3. Road Marking
• Lines, patterns, words set into applied or attached to the carriageway
or kerbs or objects within or adjacent to carriageway
To guide and control traffic on the highway
To serve as psychological barrier
To delineate traffic path and its lateral clearance from traffic hazards
To aid pedustrians and cyclists for movement into safe locations
Role of Road markings:

4. kerb

5. Road Marking Colours
Paint Material
• Ordinary road marking paint (Cold)
• Hot applied thermoplastic compound
• Reflectorized paint

8. Road Markings-Classification
Carriageway markings
• Longitudinal markings: center line, traffic
lanes, no passing zones, warning lines,
edge lines, bus lane, cycle lane
• Markings on intersections: stop lines, give
way lines, pedestrian crossings, cyclist
crossings, direction arrows, protected right
turn lanes, marking on rotaries
• Markings on hazardous locations:
carriageway width transition, obstruction
approaches, road-rail level crossings,
check barriers
• Markings for parking: parking space limits,
parking restrictions, bus stops
• Word messages: stop, slow, bus, school,
exit only
Object markings
• Objects within the carriageway
• Objects adjacent to carriageway
• Marking on kerbs

9. Carriageway Longitudinal markings
Centre line marking for a two-lane road
Barrier line marking for a four lane road

10. Double solid line for a two-lane road

11. Speed Reduction Markings

12. No overtaking zone marking at
horizontal curves MARKINGS AT A SHARP CURVE
Carriageway Longitudinal markings

13. Markings on intersections
ROAD MARKINGS ACT AS PSYCHOLOGICAL
BARRIER TO THE ROAD USER

14. Two-lane roundabout with a
single-lane exit
Markings on intersections
Two-lane roundabout with a
Double-lane exit

15. Markings on hazardous locations
Obstruction approaches
carriageway width transition
Road-rail level crossing

16. Markings for parking

17. Word messages

18. Object markings
• Objects within the carriageway
• Objects adjacent to carriageway
• Marking on road kerbs

19. Road humps (Speed breakers)

20. Transverse rumble strips
• Transverse rumble strips consist of intermittent narrow, transverse
areas of rough-textured or slightly raised or depressed road surface
that extend across the travel lanes to alert drivers to unusual
vehicular traffic conditions.
• Through noise and vibration, they attract the attention of road users
to features such as unexpected changes in alignment and conditions
requiring a reduction in speed or a stop.

21. SIGNALS
• Traffic Signals: Need, Signal face. Illumination and location of Signals,
Factors affecting signal design, pedestrians‘ safety, fixed and vehicle
actuated signals. Design of signals, Area Traffic control.

22. Intersections
• Intersection is an area shared by two or more roads. This area is designated for the
vehicles to turn to different directions to reach their desired destinations. Its main
function is to guide vehicles to their respective directions.
• Traffic intersections are complex locations on any highway. This is because
vehicles moving in different direction want to occupy same space at the same time
. In addition, the pedestrians also seek same space for crossing.
• Drivers have to make split second decision at an intersection by considering his
route, intersection geometry, speed and direction of other vehicles etc. A small
error in judgment can cause severe accidents. It also causes delay and it depends
on type, geometry, and type of control.
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23. Continued…
• Overall traffic flow depends on the performance of the intersections. It also affects
the capacity of the road. Therefore, both from the accident perspective and the
capacity perspective, the study of intersections is very important for the traffic
engineers especially in the case of urban scenario
• The intersections are of two types. They are
• At-grade intersections and
• Grade-separated intersections.
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24. Conflicts at an Intersection
• Conflicts at an intersection are different for different types of intersection.
• Consider a typical four-legged intersection
• The essence of the intersection control is to resolve these conflicts at the
intersection for the safe and efficient movement of both vehicular traffic and
pedestrians.
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25. Continued…
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26. At-grade Intersection
improvement studies
• At-grade intersections do not provide for the flow of traffic at
different levels and therefore there exist conflicts between
intersecting streams of traffic
• Intersection Volume Studies, Delay studies and accidents studies
play key role in improving the intersections
• The choice between an at-grade and grade separated junctions at a
particular site depends upon various factors such as traffic volume,
delay, economy, safety, aesthetics etc.
• Grade separated intersections generally are more expensive initially and are
justified in certain situations such as
• Express ways, free ways, motor ways
• Maximum capacity reached
• Heavy traffic volume and prolonged intersection delays
• Bad history of accidents
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27. • Grade separated intersections generally are more expensive initially and are
justified in certain situations such as
• Express ways, free ways, motor ways
• Maximum capacity reached
• Heavy traffic volume and prolonged intersection delays
• Bad history of accidents
8

28. Grade separated Intersections
• Grade-separated intersections are provided to separate the traffic in the
vertical grade.
• Different types of grade-separators are flyovers and interchange. Flyovers
itself are subdivided into
• overpass and underpass. When two roads cross at a point, if the road
having major traffic is elevated to a higher grade for further movement
of traffic, then such structures are called overpass. Otherwise, if the
major road is depressed to a lower level to cross another by means of an
under bridge or tunnel, it is called under-pass.
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29. Grade separated Intersections
• Interchange is a system where traffic between two or more roadways flows at
different levels in the grade separated junctions.
• Common types of interchange include
• Trumpet interchange,
• Diamond interchange , and
• Cloverleaf interchange.
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30. Trumpet interchange
• Trumpet interchange is a popular form of three leg interchange. If one of the legs
of the interchange meets a highway at some angle but does not cross it, then the
interchange is called trumpet interchange
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31. Diamond Interchange
• Diamond interchange is a popular form of four-leg interchange found in the urban
locations where major and minor roads crosses.
• The important feature of this interchange is that it can be designed even if the
major road is relatively narrow
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32. Clover leaf Interchange
• It is also a four leg interchange and is used when two highways of high
volume and speed intersect each other with considerable turning movements
.
• The main advantage of cloverleaf intersection is that it provides complete
separation of traffic. In addition, high speed at intersections can be achieved
. However, the disadvantage is that large area of land is required. Therefore,
cloverleaf interchanges are provided mainly in rural areas
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33. Clover leaf Interchange
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34. Traffic signals
• The conflicts arising from movements of traffic in different
directions is solved by time sharing principle
• A traffic control signal is a signal , which through its
indications , directs the traffic to stop and permits it to proceed
alternatively
• Advantages of traffic signals
• It provides for an orderly traffic movement
• It increases the capacity of the intersection
• It will reduce the frequency of certain type of accidents (
right angled)
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35. Advantages
• It provides a means of interrupting heavy traffic to cross
• It promotes driver confidence by assuring the right of way
• It may afford considerable economy over manual control
• Disadvantages
• It may increase certain type of accidents (rear end collisions)
• larger stopped delays
• When improperly located/designed it promotes disrespect
• it may encourage drivers to prefer alternate routes (under designed roads)
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36. Classification of Signals
• Traffic control signals
1. Fixed time signal (set to repeat fixed cycle of red-yellow-green lights)
2. Traffic actuated signal (time cycle/green time distribution as per the
demand of traffic flow)
• Fully actuated signal (detectors installed to sense and assign right of way)
• Semi-actuated signal (detectors installed only in minor streets)
• Speed control signal
3. Pedestrian signals
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37. Signal systems
• Synchronized system/ Simultaneous system
• All signals along the given street always show same
indication at the same time
• The division of the cycle is the same at all signalized
intersection systems and only one controller is used to
operate a series of intersections
• Alternative system
• The alternate signals or group of signals along a given road
show opposite indications at the same time
• The system is operated with a single controller. This
permits vehicles to travel one block in half the cycle time
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38. Signal systems
• Simple progressive system
• The signals controlling a street given green indications
according to a pre-determined schedule to permit continuous
operation of groups of vehicles at a planned rate of speed,
which may vary in different parts of the system
• Flexible progressive system
• It is possible at each intersection to automatically vary cycle
time and division
• Possible to introduce flashing or shutdown during off-peak
hours
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39. Concept of Signal Design: Definitions
Cycle: A signal cycle is one complete rotation through all of the indications
provided.
Cycle length: Cycle length is the time in seconds that it takes a signal to
complete one full cycle of indications. It indicates the time interval between
the starting of green for one approach till the next time the green starts.
Interval: It indicates the change from one stage to another. There are two
types of intervals - change interval and clearance interval.
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40. Concept of Signal Design: Definitions
Change interval is also called the yellow time indicates the interval between the green and red signal
indications for an approach.
Clearance interval is also called all red is included after each yellow interval indicating a period
during which all signal faces show red and is used for clearing off the vehicles in the intersection.
Clearance interval is optional in a signal design. It depends on the geometry of the intersection. If the
intersection is small, then there is no need of clearance interval whereas for very large intersections
, it may be provided
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41. Timing of signals
Timing an isolated signal
It should be determined on the following lines according to the traffic
requirements
 Cycle time should normally be from 40 to 60 sec. (best timing would be
the shortest possible under the traffic conditions). Maximum cycle time
should be 120 sec.
 Determine pedestrian crossing time of all approaches based upon pedestrian
walking speed generally taken as 1 m/s. These values will be minimum
green plus amber time for each phase
 Based on these minimum, compute green plus amber time in proportion to
approach volumes per approach lane. No phase should be less than 15 sec.
 Adjust cycle time (sum of all phases) to next higher 5 sec. interval and re-
compute phase values
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42. Timing of signals
Timing an isolated signal
 Select amber periods based upon approach speeds. Table below is
recommended as a guide for selecting appropriate amber periods
 Compute percentage value for all phases (total being 100%). It is necessary
to use % since controller settings are in % of signal cycle
 Computed timing should be installed in the controller and the operation of
the intersection observed, especially during peak conditions
 Field correction of the timing may be necessary to provide smooth flow
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43. Timing of signals
Timing a coordinated system
• The prerequisite of any coordinated system is that all signals in the system
must operate on the same cycle length. The division of the cycle may vary
with the individual intersection but the total cycle length must remain constant
• Usually the critical intersection is tuned according to the isolated signal
timing system and the resulting cycle length used throughout the system
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44. Approach speed (KMPH) Amber period (seconds)
0-50 3
50-65 4
65-80 5
80 or more 5 (plus all red period)
Timing of signals
Timing a coordinated system
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45. Concept of signal design
Phase design
• Two phase signals
Two phase system is usually adopted if through traffic is significant compared
to the turning movements. For example in figure, non-conflicting through
traffic 3 and 4 are grouped in a single phase and non-conflicting through traffic
1 and 2 are grouped in the second phase. However, in the first phase flow 7
and 8 offer some conflicts and are called permitted right turns.
This phasing is possible only if the turning movements are relatively low. If the
turning movements are significant ,then a four phase system is usually adopted
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46. Concept of signal design
Phase design
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47. Four phase signals
• There are at least three possible phasing options. For example, figure shows
the most simple and trivial phase plan. where, flow from each approach is put
into a single phase avoiding all conflicts. This type of phase plan is ideally
suited in urban areas where the turning movements are comparable with
through movements and when through traffic and turning traffic need to share
same lane.
• This phase plan could be very inefficient when turning movements are
relatively low
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48. Four phase signals
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49. Concept of signal design
Determination of Optimum cycle length
C0=(1.5 L + 5)/(1-Y)
C0= optimum cycle time
L=total last time per cycle in secs
=n(k+a-g)+R
n=no.of phases
k=green time for the phase
a=amber time for the phase
g=effective green time
R=all red time
Y=y1+y2+…yn
y1,y2,….yn are the maximum ratios of flow to saturation flow (q/s
) for phase 1, 2, ..n
s= saturation flow = 525*w pcu/hr, w= width of approach in
meters
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50. Effective green time
• Effective green time is the actual time available for the vehicles to cross the
intersection.
• It is the sum of actual green time (Gi) plus the yellow time minus the
applicable lost times.
• Lost time is the sum of start-up lost time (l1) and clearance lost time (l2)
denoted as tL.
• Effective green time , gi = Gi + Yi – tL
gi
l2
l1
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51. Effective green time
• Lane capacity:
Capacity of a lane, ci = si*(gi/C)
where ci is the capacity of lane in vehicle/hr,
si = saturation flow rate in vehicle/hr/lane,
=3600/h, h is the saturation head way in seconds/vehicle
C = cycle time in secs
The ratio of effective green time to the cycle length ( gi/C) is defined as green
ratio.
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52. Road Delineators
• Any devise or treatment whose aim is to outline the roadway
• Ex. Painted lines, raised pavement markers, posts, post mounted reflectors,
contrast treatments of the pavement
• Role
• To provide visual assistance to drivers about alignment of road ahead
especially at night
• Particularly effective in the case of complex locations involving changes in
horizontal and or vertical geometry, and during sever weather conditions
such as heavy rain, fog or snow
• Normally reflectors are used for better night visibility

53. Road Delineators-Classification
Roadway Indicators
Hazard markers
Object markers
Delineators are basically driving aids and should not
be regarded as a substitute for warning signs, road
markings, or barriers for out-of-control vehicles

54. • Decision to use is guided by type of road, fast moving traffic volume, speed,
accident experience, danger posed in alignment
• Intended to delineate the edges of the roadway so as to guide drivers about the
alignment ahead, particularly where it might be confusing for some reason
• C/S circular (dia75mm) / rectangle (80X100mm) / triangular with min. side facing
width 100mm
• black/white stripes 15cm width
• For temporary diversions, empty bitumen drums with suitable painting may be
provided
Road Delineators
-Roadway Indicators

55. Criteria to use Roadway Indicators
• Curved sections
• Horizontal curves of R>1000m
• Vertical curves with inadequate visibility
(Sight Distance) Spacing:30-50m
Straight sections
Poor visibility due to mist/fog/snow
Uncertain alignment: transition in road width,
diversions ..etc.
Road section with frequent submergence /ponding
Approaches to narrow bridges/culverts
Valley side of hill roads
Road embankment height>3m
Approaches to imp. Junctions, tunnels, causeways (s
=5-10m)
General spacing:50-70m
Radius of curve, m Spacing on curve,
m
30 6
50 8
100 12
200 20
500 35
Spacing for 1st, 2nd and 3rd posts on either
side beyond the curve = 1.8s, 3s and 6s

56. Roadway Indicators
Curve, guided by multiple chevron
alignment signs and guardrails Straight section
https://www.shutterstock.com/image-photo/road-bend-10886620

57. • Provided wherever objects so close to the road as to constitute an
accident hazard
• To define obstructions like guard-rails and abutments adjacent to the
carriageway
• Culverts, bridges, guard rails ….
Road Delineators
-Hazard markers

58. • To indicate hazards and obstructions within the vehicle flow path
• Channelizing islands, face of the kerb
• Typical locations where object markers should be used
• Traffic islands at approaches to intersections
• Around periphery of rotary islands
• Median openings
• Approaching traffic at island forming infiltration lanes
• On medians/islands on far side of the intersections
• At points where traffic divides into different directions e.g down ramps of a
grade separated intersections and
• On far side of T-junction and street dead ends
Road Delineators
-Object markers

59. Object markers-typical designs
• Enhanced delineation treatments can reduce night time crashes by
25% and 16% Reduction in non-intersection fatal and injury crashes

60. Traffic Impact Attenuators (Forgiving Road
Environment)
• Crash cushions are impact attenuators developed to prevent errant
vehicles from impacting fixed obstacles.
• The crash cushion should either decelerate the vehicle to a safe stop,
such as in a head-on hit, or redirect it safely away from the obstacle,
in the case of a side hit.
• Crash cushions are typically used where fixed objects cannot be
removed, relocated, converted to a breakaway design, or shielded by
a longitudinal barrier. Examples of application sites include exit ramp
gores where a bridge rail end or bridge pier presents a hazard, and
the ends of longitudinal barriers. Most crash cushions are patented
systems developed and tested by the manufacturer.

61. Traffic Impact Attenuators
• Most crash cushions perform their function by the principle of kinetic
energy absorption or transfer of momentum.
• In the first case, energy is absorbed by materials or devices that crush
or plastically deform, or by hydraulic devices. A rigid backup support
is required for such compression crash cushions.
• In the second case, the momentum of the vehicle is transferred to an
expendable mass, such as containers filled with sand. No rigid backup
support is needed for such “inertial” barriers.
• Some crash cushions use a combination of these principles.

62. Traffic Impact Attenuators
https://trinityhighway.com/product/adiem/
QuadGuard
Bullnose guardrail system
Crash Cushion Attenuating Terminal (CAT)
Brakemaster 350
Advanced Dynamic Impact Extension Module (ADIEM II)

63. Traffic Impact Attenuators
• Sand-filled plastic barrels
• Gravel bed attenuator
• Dragnet

64. Safety road-side rest areas/ Lay-byes
• Safety Roadside Rest Areas (A motel or motor
lodge) provide opportunities for travellers to
Safely stop, stretch, take a nap, use the
restroom, get water, check maps, place
telephone calls, switch drivers, check vehicles
and loads.
• Rest areas reduce drowsy and distracted
driving and provide a safe and convenient
alternative to unsafe parking along the
roadside.
https://beeldbank.rws.nl/MediaObject/Details/378969

65. Safety Barriers
• Rigid systems (concrete)
Used for
• Bridge approaches
• Sharp curves
• High embankments
• Flexible systems (Wire rope)
• Semi-rigid systems

66. Median Barriers
• To separate opposing traffic on divided highways
, to separate local and through traffic, or to
separate traffic in designated lanes
• Head-on-collisions, especially on highways with
narrow medians, caused by out-of-control
vehicles jumping across the medians are a major
source of accidents. Fixed objects on medians
also require shielding from the traffic flow.
• Provision of median safety barrier in such
conditions is an important requirement.

67. High embankment-recommended barrier
placement

68. Traffic Aid Posts/ Traffic patrolling vehicles
• To provide traffic safety
• Including incident management Safety measures
• Temporary barricading
• Diversion signs and safety cones