Citation

Michaels RM, Solomon D. Highw. Res. Board bull. 1962; 330: 26-39.

Copyright

(Copyright © 1962, National Research Council (U.S.A.), Highway Research Board)

DOI

unavailable

PMID

unavailable

Abstract

A study was conducted to determine whether advance information on speed changes through a visual signal system markedly changes car-following behavior. A simple signal system placed on a lead vehicle categorized speed changes into four classes--two for acceleration and two for deceleration. The driver of the following vehicle was instructed to follow as if he were in heavy traffic and wished to prevent anyone from cutting in front of him. He was instructed to watch the signal system for advance information on the speed changes of the lead vehicle. A distance measuring system was placed in the following vehicle with which it was possible to measure headway continuously to within an accuracy of 5 percent. The headway was converted to digital form and encoded on a digital recorder. Speed of the following vehicle, together with the nominal speed and acceleration of the lead vehicle, was also recorded. Speed changes in the lead vehicle were either 3 or 6 mph per sec and occurred in random order. The occurrence of a speed change was randomized over time so that the following driver did not know when or what change was to take place. The advance speed change information was presented at one of four time intervals before the onset of the speed change. A control condition was used in which no information was transmitted.

RESULTS indicated a significant reduction in mean headway when advance speed change information was presented and that headway was a minimum when the advance information was presented approximately 1 to 3 sec before the onset of the speed change. At these optimum times the variability in headway was also significantly reduced. In addition, headways were found to be independent of speed, thus, time headways decreased almost linearly with speed over the range from 36 to 54 mph.