Modification of the Highway Capacity Manual two‐lane highway analysis procedure for Spanish conditions

Ana T Moreno,David K Hale,Carlos Llorca,José E Bessa,Scott S Washburn,Alfredo Garcia

doi:10.1002/atr.1421

Abstract

SummaryThe US Highway Capacity Manual (HCM) methodology is used in Spain to evaluate traffic operation and quality of service. The effect of passing manoeuvre on two‐lane highway operational performance is considered through adjustment factors to average travel speeds and percent time spent following. The procedure is largely based on simulations in TWOPAS and passing behaviours observed during US calibrations in the 1970s. It is not clear whether US driving behaviour and vehicles' performance are comparable with Spanish conditions. The objective of this research is to adapt the HCM 2010 methodology to Spanish driver behaviour, for base conditions (i.e. no passing restrictions). To do so, TWOPAS was calibrated and validated based on current Spanish passing field data. The calibration used a genetic algorithm. The case study included an ideal two‐lane highway with varying directional traffic flow rate, directional split and percentage of trucks. The updated methodology for base conditions is simpler than the current HCM 2010 and does not rely on interpolation from tables. Copyright © 2016 John Wiley & Sons, Ltd.

Highlights

Two-lane highways have a level of interaction between vehicles traveling in the same direction and in the opposing direction, which results in unique operational characteristics, mainly because faster vehicles wishing to travel at their desired speed must use the oncoming lane to pass slower vehicles
Directional split had a profound effect on average travel speed (ATS): A concave in shape speed–flow relationship would be preferable for less favourable directional splits (20/80–40/60), while a linear relationship could better capture ATS variation with directional traffic flow for more favourable directional splits (50/50–80/20)
This study has shown the adaptation of ATS and percent time spent following (PTSF) models to Spanish two-lane highways by using field data and traffic microsimulation in TWOPAS

Summary

Introduction

Two-lane highways have a level of interaction between vehicles traveling in the same direction and in the opposing direction, which results in unique operational characteristics, mainly because faster vehicles wishing to travel at their desired speed must use the oncoming lane to pass slower vehicles (where a passing lane is not present). In order to analyse level of service, Spanish standards [1] rely on the procedures of the US Highway Capacity Manual (HCM) [2]. Given the differences in road environment, driving behaviour and vehicles’ performance, the HCM procedure would not be completely suitable for application to Spanish conditions. Field measurements can be expensive, and most importantly, they rarely provide sufficient repeatability for the full range of traffic demands; so, the conclusions may only be applicable to the observed conditions. At this point, traffic microsimulation must be considered

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Conclusion