With the motivation of figuring out the reliability of link and route traversal times, we decompose our research into two stages those summarize modeling of travel times as a link performance and the analysis on the distribution and reliability of reconstructed travel times. In a separate paper, we seek the performance of two models by adopting traffic flow theory based reconstruction approaches. An overall evaluation on freeway travel time reconstruction performance of both a macroscopic and a microscopic model are presented considering real data obtained within a case study conducted on a stretch of Istanbul freeway network. While the initial paper presents the simulation results on both day and flow direction basis, we further consider the results in the explicit analyses on distributions and reliabilities of model reconstructions in the present paper. In order to investigate the distributions of route traversal times by considering explicitly the day-to-day variations, we apply the fitness test of normal distribution to the overall reconstructions by 5 weekday data and then proceed with the standardization of reconstructions and derivation of day-to-day distributions. Statistics obtained as order moments of travel time random variable are considered in the indication of reliability.
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.
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