Impacts of automated passenger cars on the capacity of a freeway basic section: applicability in the determination of vehicle adjustment factors in mixed traffic

Abstract

The highway capacity manual (HCM) provides a formula to calculate the heavy vehicle adjustment factor (f _HV) as a function of passenger car equivalent factors for the heavy vehicle (E _T). However, a significant drawback is that the methodology was established solely based on human-driven passenger cars (HDPC) and human-driven heavy vehicles (HDHV). Due to automated passenger cars (APCs), a new adjustment factor (f _AV) might be expected. This study simulated traffic flows at different percentages of HDHVs and APCs to investigate the impacts of HDHVs and APCs on freeway capacity by analyzing their influence on f _HV and f _AV values. The simulation determined observed adjustment factors at different percentages of HDHVs and APCs (f _observed). The HCM formula was used to calculate (f _HCM). Modifications to the HCM formula are proposed, and vehicle adjustment factors due to HDHVs and APCs were calculated (f _proposed). Results showed that, in the presence of APCs, while f _observed and f _HCM were statistically significantly different, f _observed and f _proposed were statistically equal. Hence, this study recommends using the proposed formula when determining vehicle adjustment factors (f _proposed) due to HDHVs and APCs in the traffic stream.

Graphical abstract

Keywords

Connected and automated vehicles / Adjustment factors / Passenger car equivalent factors / Automated passenger cars / Freeway operation