Microsimulation of Freeway Work Zones to Assess Flow and Capacity

Horowitz, Alan J. · 2008 · ROSA P / Smart Work Zone Deployment Initiative

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Summary

This study investigates the relationship between traffic variables and capacity in freeway work zones using microscopic traffic simulation. The research addresses the limitation of existing models, such as the Highway Capacity Manual (HCM), which often fail to distinguish between two distinct flow regimes: free-flow conditions (Regime 1) and queued, stop-and-go conditions (Regime 2). The primary motivation is to provide traffic engineers with more accurate capacity estimates for work zone design and traffic impact forecasting, recognizing that capacity is influenced by stochastic variations in vehicle mix, lane distribution, and driver behavior. The methodology employed the CORSIM microscopic simulation software, specifically its FRESIM component for freeways. The model was calibrated using field data from two actual work zones on the Milwaukee freeway system, analyzed by Marquette University. Calibration involved adjusting driver sensitivity factors and other parameters to match observed flow rates and densities for both Regime 1 and Regime 2 conditions. Once calibrated, the simulation was used to conduct sensitivity tests on various prevailing conditions, including heavy vehicle percentage, road grade, upstream ramp location and volume, upstream lane distribution of trucks, and merging schemes. Each test condition was simulated multiple times to account for statistical variance. The results indicate that work zone capacity is a random variable rather than a fixed value, significantly affected by grade, vehicle mix, and the lane distribution of trucks. Specifically, heavy vehicles reduce capacity, with passenger car equivalent (PCE) factors ranging from 1.64 to 2.04 depending on the regime and work zone configuration. Grade also compounds this effect, with PCE factors increasing to approximately 2.55 at a 4% grade. The study found that restricting trucks to the right lane (away from the closed left lane) slightly increased capacity in Regime 2 conditions. Conversely, the location and volume of upstream interchange ramps had negligible effects on Regime 1 capacity, though results for Regime 2 were inconsistent. The simulation successfully replicated field-measured capacities for two-lane open configurations but required additional parameter adjustments, such as a rubbernecking factor, to accurately model single-lane open work zones. The significance of this research lies in its demonstration that microscopic simulation, when properly calibrated, can effectively assess work zone capacity under varying conditions. It highlights that capacity is not static but varies due to stochastic traffic properties. The findings provide specific PCE factors and sensitivity insights that can improve the accuracy of traffic models used for work zone planning. Furthermore, the study offers recommendations for performing such simulations, emphasizing the need to account for driver behavior randomness and the distinct impacts of different flow regimes on capacity estimation.

Key finding

Freeway work zone capacity is significantly affected by grade, vehicle mix, and the lane distribution of trucks, and behaves as a random variable due to stochastic variations in traffic conditions.

Methodology

modeling

Provenance

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Summary generated by qwen3.6-27b-prismaquant on 2026-06-10; verification: verified.

Topics

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• work zones
• traffic density