Abstract
Queue discharge flow is the most frequently observed phenomenon on urban motorways when demand exceeds capacity. Once a queue is formed, congestion arises, and the number of vehicles that can pass from downstream reduces. This reduction phenomenon is defined as the capacity drop and calculated by taking the difference between capacity and discharge flow at a road section. Obviously, this capacity drop exists after an onset of congestion and may increase in relation to weather conditions, such as rain, snow, or fog, which cause longer queues and delays. In this paper, the effect of rain on discharge flows is investigated and compared with sunny days on Istanbul urban motorways. Besides, rain precipitation during congestion is considered and related to discharge flow. Four different motorway sections were analyzed, and up to 37% discharge flow reduction was determined between sunny and rainy conditions. Motorway sections with higher free flow speed (FFS) were found to be more affected by rain, and discharge flow reduction was bigger compared to the section with the lowest FFS. For 1 mm/m2/h of precipitation, the discharge flow is estimated as 1,719 pcu/h/lane when FFS is 84 km/h, and as 1,560 pcu/h/lane if FFS is 104 km/h.
Highlights
Traffic congestion is a daily routine, especially for commuters, who use their private cars during morning and evening peak hours
This paper mainly focuses on discharge flow change on basic motorway sections in İstanbul, where the flow is interrupted due to traffic demand
Along Istanbul urban motorways, 84 sunny and 52 rainy discharge flows were determined from four sections, where two RTMSs were present at each section
Summary
Traffic congestion is a daily routine, especially for commuters, who use their private cars during morning and evening peak hours. Once a queue is formed, if the demand remains the same, less flow can be discharged at the downstream This phenomenon is called ‘capacity drop’ and could be defined as a reduction at mainstream flow after onset of queue on the upstream, or basically the difference between capacity and discharge flows [1,2,3]. In this statement, the discharge flow indicates the outflow of congested vehicles without influence of any downstream queues. They can vary between different traffic lanes in the same cross-section of a carriageway [4]
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