Driver Workload at Higher Speeds (0-5911-1)

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.