Driver perception-response time is one of the most argued variables among experts in human factors, driver behaviour, and crash reconstruction.  Although several studies have been conducted to study drivers’ perception and response to certain roadway hazards, some common collision scenarios have not been thoroughly investigated.

In order to increase accuracy and certainty in crash reconstruction involving assumptions about driver responses, our experts at Kodsi Engineering have been working in collaboration with the University of Guelph to study Driver Response Time (DRT) to 4 common hazard scenarios. This article summarizes the results published in 3 Society of Automotive Engineers (SAE) technical papers: DRT to mid-block crossing pedestrians ; DRT to cyclist path intrusions ; DRT to left-turning oncoming vehicles.

The responses of about 100 volunteer participants were studied in a biofidelic full car body simulator. The simulator re-created a natural driving experience using 300 degree wrap-around projections, with the research benefits of including data acquisition systems to track and record eye and human motions on typical roadways (and excluding the possibility of any real crashes or injuries!).

Figure 1: Oktal full car body simulator

Figure1: Oktal full car body simulator


Figure 2: Vicon 12-camera motion capture


Figure 3: Tobii Pro mobile eye tracker


Over an approximately 10 minute drive each participant encountered all 4 hazard types in random order, and we measured their “Driver Response Time” (DRT) as:

  • Brake-response time (BRT) – when the object became a hazard until driver reacted by touching the brake pedal
  • Swerve-response time (SRT) – when the object became a hazard until driver turned the steering wheel 2 degrees
  • Brake & Swerve-response time (BSRT) – when object became a hazard until driver touched the brake pedal or turned the steering wheel by 2 degrees

While driving in the simulator, research participants encountered the following scenarios.

Vehicle-Pedestrian Crash Scenario 

Why study this scenario?

With a 12% increase in crashes with pedestrians from 2006 to 2015, vehicle-pedestrian collisions account for 15% of fatal crashes. Perception response times (PRT) to pedestrians crossing from the far curb were not previously studied.

Study Results Summary

Where the pedestrian jogged from the opposite curb, the time to impact was 4.35 seconds:

  • The mean response time was 1.46 seconds (this value was close to the 1.5 seconds seen in other literature).
  • 90% of drivers only braked
  • 8% only swerved
  • 2% swerved and braked

Only 8% of drivers who braked got into a collision, and none of the drivers who swerved got into a collision.

Figure 4: Pedestrian’s first step onto the road was chosen as the onset of the DRT value



Why study this scenario?

There are more cyclists on the road than ever before – there were 51 million on the road in 2012, and by 2017 that number increased to 66 million). Hence it is not surprising that there has been a 6% increase in crashes with cyclists from 2006 to 2015 despite increased awareness and safety measures such as dedicated bicycle lanes. Our study focused on the perception response times (PRT) of through drivers reacting to cyclists who failed to stop at a stop sign and rode into the path of the vehicle, a typical scenario which had never been studied previously.

Study Results Summary

Where the cyclist fails to stop at stop sign and intrudes from the near side of intersection, with the time to impact being 3.26 seconds:

  • The mean response time was 1.93 seconds.
  • 80% braked
  • 20% swerved

Interestingly, the participants were more likely to brake than to swerve; however, only 15% of those who braked ended up crashing, while 100% of those who swerved ended up crashing.

Left-Turning Vehicles

Why study this scenario?

Although left-turn crashes account for almost one quarter of all collisions, research is lacking for driver responses to realistic left-turning vehicle acceleration.

Study Results Summary

Our studies looked at two types of left-turning hazard scenarios at an intersection – those where the oncoming vehicle was initially stopped at the signalized intersection before proceeding to turn left (“LHTS” in summary below), and those where the oncoming vehicle did notstop and turned left right away (“LHTNS” below). The first lateral movement of the left-turning vehicle was chosen as the onset of the DRT.

LHTS scenario:

With a time to impact of 4.00 seconds:

  • The mean response time was 2.67 when the vehicle started moving from a stop.
  • 60% only braked
  • 14% only swerved
  • 20% braked and swerved
  • 6% released the accelerator

LHTNS scenario:

With a time to impact of 4.00 seconds:

  • The mean response time was 2.0 seconds when the vehicle was moving at a constant speed.
  • 51% only braked
  • 23% only swerved
  • 23% braked and swerved
  • 2% accelerated and swerved

The driver response time to the initially stopped left-turning vehicle were quite a bit longer (34%) than the left-turning vehicles that were not stopped. The initially stopped vehicle appears to have been harder to detect especially in the beginning phase of acceleration since it would be moving slower.


A pre-requisite to crash avoidance evaluation is accurate information about a driver’s perception-response time to similar hazards.  These three new published studies summarized above allow the industry to use more accurate estimates in their calculations and analysis when assessing whether collisions with a left turning vehicle, cyclist, or pedestrian are potentially avoidable.



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