Analysing the impact of traffic incidents on express road traffic flow using FREEVAL

Ciszewska-Kulwińska, Eliza; Romanowska, Aleksandra; Kustra, Wojciech · 2018 · Crossref

DOI: 10.1051/matecconf/201823101008

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Summary

This study investigates the impact of traffic incidents on express road traffic flow, specifically analyzing how disruptions affect travel time and vehicle speed. The research is motivated by the frequent occurrence of accidents and road works on motorways, which cause significant delays and deteriorate driving conditions. While accident data is available, comprehensive records for other incidents like collisions or short-term works are often incomplete. Understanding these impacts is crucial for real-time traffic management and road network planning. The authors aim to quantify these effects using simulation tools to complement missing empirical data. The methodology employs FREEVAL, a macroscopic simulation software based on the Highway Capacity Manual (HCM) and the Cell Transmission Model. The study focuses on a 3 km section of the S6 express road (Tri-City Ring Road) in Gdańsk, Poland, characterized by high traffic volumes exceeding 77,000 vehicles daily. The model was calibrated using traffic data from a typical weekday in December 2014, focusing on the afternoon peak period. The researchers analyzed 156 scenarios, including a baseline with no incidents and various incident scenarios involving blocked shoulders, one lane blocked on two-lane sections, one lane blocked on three-lane sections, and two lanes blocked on three-lane sections. These incidents were simulated for durations ranging from 15 to 60 minutes across different segments of the road. The results demonstrate that the severity of traffic disruption depends heavily on the number of lanes blocked and the road's cross-section. Blocking the right shoulder had a negligible impact, increasing travel time by no more than 3% and affecting traffic only while the incident was active. In contrast, blocking one lane on a two-lane section caused significant delays, with travel time increasing by up to 560% in the worst-case intervals. The impact dissipated slowly, with normal conditions taking up to 30 minutes to restore after a 15-minute incident. Blocking one lane on a three-lane section resulted in lower increases, up to 300%. The most severe disruptions occurred when two lanes were blocked on a three-lane section, causing travel time increases of up to 3,600% and average speeds dropping to 22 km/h. In these cases, the impact duration was three times the incident duration, with delays persisting for 45 minutes after a 15-minute blockage. The study concludes that simulation tools like FREEVAL are valuable for assessing incident impacts where historical data is scarce. However, the authors note limitations due to the inability to fully calibrate the model for Polish conditions, specifically regarding capacity and free-flow speed adjustment factors. The findings highlight that lane blockages, particularly on narrower cross-sections, create prolonged bottlenecks that significantly extend travel times well beyond the incident's duration. The paper suggests further research to verify these modeling results with empirical data to improve the accuracy of traffic impact assessments in Poland.

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