Driver Workload at Higher Speeds

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K. Fitzpatrick, S.T. Chrysler, E. Park, A.A. Nelson, J.A. Robertson, V. Iragavarapu

Publication Date:

February 2010


The goal of this Texas Department of Transportation project was to gain a better understanding of driver performance at high speeds. Specific efforts included the following studies:
  • The Closed-Course Pilot Study consisted of observing and recording the activities and actions of a series of drivers following a lead vehicle going either 60 or 85 mph.
  • The Open-Road Pilot Study recorded participants driving between Odessa and Pecos, Texas, within 70- and 80-mph sections.
  • The Simulator Pilot Study determined driver reactions to a looming vehicle (both passenger car and large truck) and also generated directions for how to conduct the Phase II simulator study.
  • The Simulator Phase II Study collected brake reaction to a vehicle looming in the driver's view for 50 participants. Conditions varied included initial speed, lead vehicle type, lead vehicle deceleration rate, and workload level.
  • The Following Distance Study used data from traffic counters to identify speed and axle gap data on freeways with 60-, 70-, and 80-mph posted speed limits.
  • The Gaps at Passing Study measured gaps during passing maneuvers for daylight conditions on freeway sections.
When responding to a vehicle slowing in their lane, drivers in the Simulator Phase II Study at the 85-mph speed had a reaction time that was statistically longer than that of drivers at the 60-mph speed. In the simulator, on-road, and test track studies where researchers directly measured driver performance, performance declined when a driver was multitasking at the higher speed. The traffic counter data showed that axle clearance distance was larger for the 80-mph freeway sites as compared to the 60- and 70-mph speed limit sites, both statistically and practically. The Gaps at Passing Study found a different result; drivers used similar passing gap distances on both 70- and 80-mph sections.

Report Number:



Freeway, Driver Workload, High Speed, Passing Gap, Following Distance, Reaction Time

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