Passenger Car Equivalent Value for Commercial Vehicles: A New Approach

Bouhouras, Efstathios; Basbas, Socrates · 2021 · Crossref

DOI: 10.3311/pptr.15439

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Summary

This paper addresses the need for accurate Passenger Car Equivalent (PCE) values for commercial vehicles in traffic engineering, specifically within the context of the Municipality of Thessaloniki, Greece. The PCE factor converts heterogeneous traffic streams into a homogeneous stream of passenger cars, a critical step for calculating traffic parameters such as saturation flow. While the Highway Capacity Manual (HCM) provides a standard PCE value of 2.00 for commercial vehicles, the authors argue that even slight variations in this value can significantly impact traffic study outcomes. The research aims to develop and validate a new methodology for calculating PCE based on field data, comparing the resulting value against the HCM standard to assess its practical implications. The study employed a headway-based methodology derived from an extensive review of international literature. Researchers selected 27 at-grade, signalized intersections in Thessaloniki that served as main entry points or primary arterial roads with significant commercial vehicle volumes. Field surveys were conducted during the morning period (07:00–14:00) in May–June 2016, as local regulations restricted daytime goods distribution. Data collection utilized the JCT Traffic Tools application on Android devices, allowing observers to record headways for 20 consecutive green light phases per lane without expensive video equipment. The initial dataset comprised 16,000 vehicles across 3,177 green light phases. To ensure data quality, the authors applied strict filtering criteria: headways exceeding 3.00 seconds were excluded to remove non-congested traffic, and lanes were analyzed only if they met specific movement and congestion thresholds. This process reduced the sample to 3,379 valid headway values from 11 intersections and 16 lanes, which were then used to calculate prevailing saturation flow rates. The analysis yielded an average PCE value of 2.18 for commercial vehicles in the study area, which is higher than the HCM standard of 2.00 and the official Greek value of 2.00. The authors validated this finding by calculating adjusted saturation flow rates using the derived PCE; for 13 out of 16 fully congested lanes, the ratio of prevailing to adjusted saturation flow exceeded 1.00, confirming the appropriateness of the 2.18 value. The study demonstrates that the proposed methodology, while requiring a significant number of surveyors, offers a reliable alternative to video-based HCM methods by allowing observers optimal positioning and reducing equipment costs. The significance of this research lies in its demonstration that PCE values are context-dependent and should not be treated as universal constants. The difference between the calculated value (2.18) and the standard value (2.00) can produce significant impacts on transportation studies, particularly in areas with high commercial vehicle volumes. The authors conclude that the developed methodology should be applied in specific transportation studies to ensure accuracy, acknowledging that PCE values must be constantly updated to reflect changing traffic conditions, volumes, and densities. This approach provides a practical, low-cost framework for deriving localized PCE values, enhancing the precision of traffic capacity analysis.

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