Abstract
Freeway management systems that rely on single-detector data acquisition generally use a simple equation to calculate speeds. In this paper, the validity of that equation is tested using data from two locations in ontario, collected using paired-detector speed traps. The results show that the equation gives biased estimates of speeds over a major portion of the range of operating conditions. Discussion of possible causes demonstrates that at least two key assumptions underlying the equation are not met by actual traffic. This result has important implications not only for operation and design of freeway traffic management systems, but also for theoretical work, such as that on speed-flow relationships.