Impact of Roadside Friction on Traffic Flow Characteristics at Midblocks under Mixed-Traffic Conditions: Comprehensive Review

Roadside friction, the resistive forces that are exerted through traffic by activities along the carriageway edge or shoulder, significantly influences traffic performance. These activities reduce effective roadway width, leading to speed reductions, capacity constraints, poor levels of service (LOS), and safety hazards. Although developed countries with homogeneous traffic conditions manage such factors effectively, mixed-traffic conditions in regions like India exacerbate their impact. Addressing friction elements is crucial for developing effective traffic management strategies, improving road efficiency, and refining highway capacity manuals. This paper reviews three decades of research on midblock road sections, examining side friction’s influence on key traffic parameters such as speed, capacity, delay, congestion, and LOS. Additionally, it evaluates different methodologies employed to quantify these effects, including regression models, simulation techniques, and capacity adjustment factors. Moreover, the authors made an effort to identify and delineate the research gaps, with the intent of opening new avenues of study on the multifaceted impacts of side friction.