This document summarizes research on evaluating overtaking sight distance using drivers' psycho-emotional responses rather than just physical road parameters. The researchers measured galvanic skin response and heart rate in over 120 real overtaking maneuvers to determine when drivers felt stress. They found that standard sight distances are insufficient for over half of observed maneuvers. Drivers often overtake without safe information or exceeding the speed limit. Measured sight distances exceeded design values by 20-40%, so more research is needed to understand drivers' emotional responses during overtaking.

1. Evaluation of Overtaking Sight
Distance Using a Driver’s
Psycho-emotional Response
Authors: Dr.sc.ing. Atis Zariņš (Riga Technical University)
Dr.sc.ing. Līga Plakane (University of Latvia)
M.sc.ing. Jānis Smirnovs (Riga Technical University)
ICDBT 19th August 2013, Helsinki

2. Goal and main challanges of
the research
Determine the necessary overtaking
distance using drivers psycho-
emotional response not physical
parameters of the road
• Measure drivers psycho-emotional
responses during real-life overtaking
manoeuvres
• Compare measured overtaking distances
with ones calculated according to design
code LVS 190-1

3. Review of the problem
• In Latvia only 0,3% of road accidents happen
during overtaking manouvre, but they cause
5% of all fatalities and 1% of injuries in road
accidents overall
• In accidents caused by inapropriate overtaking
more that two cars are involved up to 20%
more often than in other types of road
accidents
• Usually overtaking distace is calculated taking
into account only physical parameters of the
road and not taking into account drivers
psycho-emotional response

4. Object of the research
The classic approach is based on evaluation of three distances:
• the distance travelled from decision to aligning with the vehicle to
be overtaken (d1)
• the distance travelled from aligning with the vehicle to be
overtaken to returning back into the lane (d2)
• the distance travelled by oncoming vehicle during both of the
above operations (d3)
The sum of these three distances, plus a safety distance (d4),
defines necessary overtaking sight distance that must be
considered for each section of road where overtaking is allowed
Source: «Grades and Sight Distances» The University of Southern Queensland

5. Design standart LVS 190-1
• The overtaking sight distance (So) is defined as the
distance on the road necessary for the driver to perceive
the oncoming vehicle and safely complete desired
overtaking manoeuvre while driving with a V85 speed
• Overtaking sight distance consists of both distances
travelled (by oncoming and overtaking vehicles), as well
as the safety distance between them, or So= S1+ S3+S4
Vehicle at the begin of manoeuvre
Vehicle at the end of manoeuvre
Symbols:
Overtaking sight distance (So)
Distance traveled by overtaking vehicle (S1) Distance traveled by
oncoming vehicle (S3)
Safety distance (S4)
Distance traveled by
overtaken vehicle (S2)
V = V1 85
V = 1,1 V1 85
· V = V3 85

6. Drawbacks of LVS 190-1
approach
• The overtaking sight distance directly depends
on selected speeds of all three vehicles
involved. In reality speeds can differ from that
assumed
• The overtaking sight distance also directly
depends on purely physical parameters of
involved vehicles such as length, weight,
power, equipment etc.
Therefore, it may be more productive to use
direct indicators observed in a driver’s behaviour
and his/her physiological reactions during the
overtaking manoeuvre to define the necessary
overtaking sight distance

7. Methodology of research
• Two human physiological parameters were
measured concurrent with a video
recording of traffic situation on the road
visible for the driver
– galvanic skin response (GSR)
– heart rate (HR)
• During actual real-time medium intensity
traffic on one carriageway two lane
roads, more than 120 overtaking
manoeuvres were recorded and analysed
• Eight drivers of varying age and both
genders were research subjects

8. Typical record of overtaking
episode
• In most cases the beginning and the end of the overtaking
episode appears in the GSR record as the “tipping points”
followed by first increasing and then decreasing dielectric
permeability of the skin
• These main points allow an accurate determination of the
beginning and the end of the manoeuvre
• The start and end of the manoeuvre were always verified
by video fixing the exact location of the car on the
roadway

9. Usage of gathered data
• Based on the physiological response data for
each overtaking episode, it was possible to
determine the exact beginning and exact end
of the manoeuvre
• In this way, the actual distance used for
manoeuvre can be compared with one, used
in a road design practice and set in road
design codes
• From our observed data, it is possible to
evaluate in what extent the required
overtaking sight distance values correspond to
the real driver needs and for proper decision-
making

10. Measured results compared to
calculated results according to
design code

11. Distribution of overtaking
distances
• The average distance was found to be
between 200 and 550 meters in length
• According to the calculations of design
code, the value of distance is 350
meters

12. Distribution of overtaking
speed
• The distribution of overtaking speed led to
conclusion, that there dominate maximal
allowed speed or that exceeded up to 10
km/h. Some lower speeds were fixed in
situations with reduced allowed speed
• About 20% of overtakes were performed
using significantly excessive speed

13. Heart rate measurements
• It was observed that HR fluctuations during an
overtaking manoeuvre were either non-existent
or so minimal as to not attain detection threshold
with any consistency
• Therefore information about emotionally-based
physiological responses mostly contains in GSR
records

14. GSR records
• Responses in traffic situations during
overtaking differ according to whether an
oncoming vehicle is involved
• An oncoming vehicle reveals a much larger
amplitude of response in episodes (2 and
4) than without oncoming vehicle (1 and 3)

15. Common patterns for GSR
measurements
• The response is divided into two
distinct stages with division near or in
an aligned position with overtaken
vehicle. This can be explained by
involving two relatively separate
decisions, the first of which relates to
the initiation of the manoeuvre and
second one to completing the
manoeuvre
• The second part of manoeuvre
produces larger response
(GSR), than the first one, especially
when an oncoming vehicle exists.
That can be explained by greater
importance of information to be
gained and processed for decision-
making and completion of overtaking
manoeuvre

16. Conclusion based on gathered
data
It can be assumed, therefore, that an overtaking
decision actually consists of two parts, with the
second part depending on the perceived
situation in the middle of manoeuvre. The
previous approaches, based on assumptions of
only physical and mechanical factors, are not
consistent with the actual process performed by
the human being – the driver – and may in fact
be dangerously inadequate

17. Conclusions
• The standard overtaking sight distance
is insufficient regarding to more than
half of analysed cases
• According to LVS 190-1, design value
of overtaking sight distance (So)
corresponding to V85=100 km/h is
625m. This design distance
corresponds with a probability of no
more than 50% to the distance derived
by real-time data

18. Conclusions
• In most cases drivers are tended to make
a decision to overtake either without safe
and sufficient information, or by exceeding
the speed limit
• According to the data collected, the
estimated necessary overtaking sight
distance exceeds existing design values by
about 20 to 40%
• More studies should therefore be
undertaken to understand the essence and
importance of particular driver responses
in detail

19. Thank you for attention!