Abstract
Observations of motorist response to the amber phase of traffi( signals obtained at five intersection,representing three speed zonds are presented. The data give an estimate of the probabilj ty of stopping for vehicles as a function of their distance fr from the intersection at the onset of the amber phase of the traffic signal. The results lend no support to a popular hypo- thesis that is that driveI'S tend to "take advantage" of a long amber phase by treating it as an extension of the greeno The re sul ts of the study are compared wi th othe r inve stiga,tions pertaining to amber phase lengths and implications or this work for the design of amber phases are discussed.