This experiment is one in a series exploring human factors issues related to the Automated Highway System (AHS). The comfort level of the driver of the lead vehicle of a string of automated vehicles was determined (a) under normal AHS operating conditions, and (b) while a second vehicle was joining the string as the new lead vehicle. The experiment was conducted in the Iowa Driving Simulator. A generic AHS configuration was used--the left lane was reserved for automated vehicles, the center and right lanes contained unautomated vehicles, the center lane was not a dedicated transition lane, there were no barriers between the automated and unautomated lanes. Sixty drivers participated in the experiment--half male, half female; half between the ages of 25 and 34 years, half 65 or older. The experiment began with the simulator vehicle leading a string of vehicles in the automated lane--it was controlled by the AHS and traveling at the design velocity. A second vehicle entered the automated lane ahead of the simulator vehicle, traveling at 88.6 km/h (55 mi/h). It began to accelerate and the gap between it and the simulator vehicle decreased. It accelerated until its velocity matched the design velocity--then, it became the new leader of the string of vehicles. While the gap between the entering vehicle and the simulator vehicle was decreasing, the comfort level of the driver was monitored. The experiment determined the effect on the driver's comfort level of varying: the design velocity, the inter-string gap, the time at which the second vehicle entered the automated lane, and the age and gender of the driver. Results were as follows: (1) When the simulator vehicle led a string of automated vehicles operating normally, with a fixed inter-string distance between it and the string ahead, positive comfort levels were recorded on 89.9% of the trials; (2) When the simulator vehicle lead a string of vehicles operating normally, the comfort level varied with the gender of the driver--the mean comfort level was higher for male drivers than for female drivers; (3) When a second vehicle entered the automated lane ahead of the simulator vehicle, in 86.2% of the trials the comfort level of the drivers decreased, and in 71.6% of the trials it decreased to a negative comfort level; (4) When a second vehicle entered the automated lane, the comfort level varied with both gender and age--the mean comfort levels were -0.37 for younger males, -0.45 for younger females, -0.54 for older males, and -0.71 for older females; and (5) There were indications that the sharp decrease in comfort may have been triggered by time to collision estimates, although it does not provide a complete explanation.

  • Corporate Authors:


    3660 Technology Drive
    Minneapolis, MN  United States  55418

    Federal Highway Administration

    Turner-Fairbank Highway Research Center, 6300 Georgetown Pike
    McLean, VA  United States  22101
  • Authors:
    • Bloomfield, J R
    • Christensen, J M
    • Carrol, S A
    • WATSON, G S
  • Publication Date: 1996-4


  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 70 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00724995
  • Record Type: Publication
  • Report/Paper Numbers: FHWA-RD-95-107, Working Paper
  • Contract Numbers: DTFH61-92-C-00100
  • Files: TRIS, ATRI, USDOT
  • Created Date: Aug 29 1996 12:00AM