Kf. Petty et al., ACCURATE ESTIMATION OF TRAVEL-TIMES FROM SINGLE-LOOP DETECTORS, Transportation research. Part A, Policy and practice, 32(1), 1998, pp. 1-17
As advanced traveler information systems become increasingly prevalent
the importance of accurately estimating link travel times grows. Unfo
rtunately, the predominant source of highway traffic information comes
from single-loop loop detectors which do not directly measure vehicle
speed. The conventional method of estimating speed, and hence travel
time, from the single-loop data is to make a common vehicle length ass
umption and to use a resulting identity relating density, dow, and spe
ed. Hall and Persaud (Transportation Research Record 1232, 9-16, 1989)
and Pushkar et al. (Transportation Research Record 1457, 149-157, 199
4) show that these speed estimates are flawed. In this paper we presen
t a methodology to estimate link travl times directly from the single-
loop loop detector flow and occupancy data without heavy reliance on t
he flawed speed calculations. Our methods arise naturally from an intu
itive stochastic model of traffic how. We demonstrate by example on da
ta collected on I-880 data (Skabardonis et al. Technical Report UCB-IT
S-PRR-95-S, Institute of Transportation Studies, University of Califor
nia, 1994) that when the loop detector data has a fine resolution (abo
ut one second), the single-loop based estimates of travel time can acc
urately track the true travel time through many degrees of congestion.
Probe vehicle data and double-loop based travel time estimates corrob
orate the accuracy of our methods in our examples. (C) 1998 Elsevier S
cience Ltd.