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

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

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

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

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

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

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

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

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

Measured results compared to calculated results according to design code

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

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

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

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)

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

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

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

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

Thank you for attention!