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The technology of bus and coach systems
Published in Peter White, Public Transport, 2017
Consider a busy traffic-light-controlled urban intersection between two main roads. The ‘stop line’ is that at which all traffic stops during the red and amber phases for that approach, prior to crossing or turning at the junction. Vehicles approaching the junction from one direction can thus pass through immediately when the green phase is displayed, but not during the red or ‘inter-green’ (amber) phases. The ‘cycle time’ is that over which the same sequence of phases is applied. Under heavy traffic conditions, this effectively becomes a fixed cycle in most cases (a comprehensive description of traffic engineering concepts and applications is provided by Slinn et al.2006). For example, if the total cycle time were 110 seconds, and on one particular approach this comprised a red phase of 50 seconds, and a green phase of 50 seconds, each separated by five seconds inter-green (during which no flow is assumed to take place), and all buses can pass through during the next available green phase, the minimum delay would be 0 seconds, with a maximum of 60, and an average of about 16 seconds. A bus arriving at the stop line just as the green phase ends would encounter a delay of 60 seconds (red plus two inter-greens) before being able to cross the stop line. On a service with a very short headway (for example, three minutes) this itself could introduce perturbation in the schedule, as a delay of one minute to a bus is significant in relation to headway.
Lane-based analysis of the saturation flow rate considering traffic composition
Published in Transportation Planning and Technology, 2023
Anas A. Mohammad, Hazem M. Al Nawaiseh, Wael K. Alhajyaseen, Charitha Dias, Babak Mehran
Turning Movement Counts (TMC’s) for many types of intersections across Qatar were carried out during the period from August 2017 until December 2018 using recorded videos. The cameras were installed at each approach by taking into consideration the sun-glare/distance of vehicles from camera/angles and high enough to view both stop line and queued vehicles. Twenty-four sites were carefully selected to ensure that the sites are not affected by traffic diversion, bus stop and on-street parking within 75 m of the stop line and downstream, uncontrolled pedestrian crossing, and narrow lane width (standard lane width 3.65). These recorded videos were utilized to manually measure the headway time and the number of passing vehicles from the recorded 9 h of videos during peak periods which were used to calculate the SFR value as per Equation (2). Table 1 provides a summary of the selected sites used for data collection and Figure S3 depicts selected intersections location. Almost more than 3335 cycles and 62,000 vehicles were observed to measure the headway at the 24 sites described in Table 1. Many readings were observed where three through lanes exist at intersections since most signalized intersections in Qatar have three lanes through. Notwithstanding, a considerable amount of measurements were observed at other intersections with various through lanes arrangement (almost more than 1000 cycles and 19,000 vehicles used for headway measurements). The analyzed lanes are those with exclusive through movement which is not shared with right turn movement or left-turn movement. The study sites had level upstream and downstream approaches (level: grade < ±2%). In each analysis signal cycle, a minimum of 10 queued vehicles at the end of the red phase should be present to undertake the SFR analysis. This is in line with HCM 6th Edition (2016) (Transportation Research Board 2016) which suggests that after the fourth vehicle has been discharged, the saturation flow is achieved and sustained. Figure 1 illustrates the method used to measure the headway to estimate SFR for through lanes at Intersections. The data of outer through lane at approaches that do not have exclusive right turn lane were not used to remove the right turn effect. It is also important to mention that all sites had a median separated left turn lanes, which indicates no interaction between left turning and through movements.