Factors affecting operational capacity of urban arterial streets under heterogenous traffic conditions: A narrative review paper

Lubna N.Abdullah; Zainab Ahmed  Alkaissi

doi:10.71229/ehaaqb47

Authors

Lubna Najim Abdullah Highway and Transportation Engineering Department, Mustansiriyah University, Baghdad, Iraq
Zainab Ahmed Alkaissi Highway and Transportation Engineering Department, Mustansiriyah University, Baghdad, Iraq

DOI:

https://doi.org/10.71229/ehaaqb47

Keywords:

Operational capacity, Traffic composition, Roadside friction, Passenger car unit, Heterogenous traffic

Abstract

Urban arterial streets operated under stochastic roadway, traffic, control, and roadside conditions. Stochasticity makes their operational capacity difficult to represent by a single fixed value. This paper reviewed the principal factors affecting operational capacity. A two-stage thematic narrative review was conducted to identify the factors influencing the operational capacity of urban streets. The first stage involved reviewing and classifying the factors listed in the Highway Capacity Manual, the Indian Highway Capacity Manual, and Transport for London Technical Note10 , and comparing them. In the second stage, relevant scientific studies were reviewed, and their results were categorized according to the main factor groups adopted in the selected guidelines. The influencing factors grouped into geometric characteristics, traffic composition, control conditions, roadside friction, environmental and temporary conditions, and emerging intelligent transportation technologies. No strict time limit was adopted to retain the foundational studies and cover factors that had not received sufficient attention in recent literature. The reviewed papers showed that lane width, number of lanes, access point density, traffic composition, signal timing, green-time allocation, coordination, curbside parking, public transport stops, vehicle pick-up and drop-off activities, and adjacent land use could substantially alter capacity. The findings also indicated that capacity values were sensitive to local driving behavior and the conversion of heterogeneous traffic into passenger car units. The review concluded that transferring fixed roadway capacity values between cities could produce inaccurate estimates. Locally calibrated, field-based capacity estimation methods that consider traffic, geometric, control, and roadside variables were considered the most appropriate basis for capacity estimates in heterogeneous urban traffic.

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