Citation

Courage KG, Showers RH, McLeod DS. Transp. Res. Rec. 1995; 1484: 40-49.

Copyright

(Copyright © 1995, Transportation Research Board, National Research Council, National Academy of Sciences USA, Publisher SAGE Publishing)

DOI

unavailable

PMID

unavailable

Abstract

Although the Highway Capacity Manual (HCM) modeling process is widely accepted, there is evidence of significant disparity between estimated arterial travel speeds and speeds measured in the field. The HCM suggests that speed and travel time values measured in the field are preferable to the computed estimates. Often the validity of the model estimates may be challenged by competing interests. The primary objective was to reconcile the differences between estimated and measured travel times on arterial streets. The principal product is a set of recommendations for modifying the estimation and measurement procedures to reduce the disparity between them. Four tasks were involved: (a) examine the arterial speed computational methodology to identify sources of disagreement with field measures performed with moving vehicles, (b) compare a large sample of measured travel speeds with travel speed estimates carried out using the HCM methodology, (c) develop candidate adjustment factors that can be applied in practice to improve the agreement between estimated and measured speeds, and (d) test the candidate adjustment factors against the field data and recommend specific modifications to the travel time procedures and the HCM model. Although the HCM models were intended for analyses on the planning and operational level, the focus here is on planning applications. The main differences between planning and operational analyses are in the levels of detail of the input data and in the required level of accuracy of the results. It is important in either case that the travel time estimates be unbiased, that is, the procedures should not consistently underestimate or overestimate the travel times. The results offer a reasonable explanation for the apparent discrepancies between estimated and measured travel times and delays on arterial streets. They also provide a practical means of adjusting the estimated delay values to produce a very close agreement with the corresponding measurements.

Language: en

Keywords

Mathematical models; Highway traffic control; Roads and streets; Motor transportation; Highway administration; Highway planning; Urban planning