Estimating percent-time-spent-following on two-lane rural highways

This study concentrated on estimating the percent-time-spent-following (PTSF) on two-lane highways. This measure is a key estimate of level-of-service in traffic engineering applications. Its evaluation to date has been based on simulations that yielded over-estimated values. The present study shows how to estimate this variable from easily obtained field data based on queuing theory. The estimates accord with opinions on yielding significantly lower values of PTSF that are expressed in the relevant traffic literature. An improved relationship between PTSF and two-way flow is provided by fitting the new estimates by means of the least-squares method.

► Number of gaps inside platoons on rural highways are distributed geometrically.
► Thus, platoons behave like waiting lines in M/M/1 queue, that assumed in the sequel.
► PTSF becomes then a simple function of average gaps inside and outside queues.
► Therefore PTSF may be measured from simple count data.
► The resulting PTSF is lower than the values published in the HCM.