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PDF (DX094490.pdf) - White Rose Etheses Online

PDF (DX094490.pdf) - White Rose Etheses Online

41 flow at the Arundel

41 flow at the Arundel Gate entry. There are long queues and delays at Arundel Gate as a result of this. It is of interest to note that High Street is used mainly by buses as it is a no-through road for all other classes of vehicles. Two immed- iate results are that (1) only a small proportion of the entering flow at Arundel Gate turns left; and (2) the circul- ating flow has a high percentage of buses. This arrangement of flows allows vehicles from the nearside lane of Arundel Gate to merge with the circulating flow, rather than accept offered gaps. Data from the other two lanes only were taken into account. Park Square Roundabout (Rig. 3.3) is a large size roundabout, having six entries and seven exits. It is near the city centre and provides the entry to the main link road with the £41 Motorway. The entry from where data was collected is the Corn Exchange which is the immediately previous entry to the Parkway (the Ml link road). During the evening peak period heavy flows from Sheaf Street and Commercial Street, directed towards the Parkway, cause long queues and delays to traffic entering from Corn Exchange. The entry has four lanes at the stop. line, however the flow from the nearside one is not seriously impeded by the circulating flow, allowing entering vehicle to filter into the junction and exit at the Parkway. It should be noted that traffic entering from the Parkway during the morning peak period was subjected to extremely long delays; to alleviate this condition traffic signals have been installed to the junction since the observations collected for this project, changing radically the operation of this roundabout. At all sites the entry under study was recorded S*FtELD UNVERSTY

42 using a SONY AV342OCE portable monochrome video tare recorder, belonging to the Civil and Structural Engineering Department of the Uiiversity of Sheffield. The duration of each observation was thirty minutes as all of the entries were not saturated for longer periods. The resulting tapewas subsequently transferred in the laboratory onto another tape on which a time base was superimposed using a National NV.8030 recorder and an Aston NIT video number generator to generate the time base. This tape subsequently was analysed by being played back on a monitor using the slow and stop motion facilities of the National recorder. The time base was accurate to an 1/50th of a second. Therefore the available gaps of the circulating flow as offered to the entering traffic could be easily abstracted. The headway measurements were concerned with the time interval between successive vehicles moving along the circulating carriageway, though not necessarily in the same traffic lane. These head- ways are referred to also as 'gaps'; however this does not imply that the quantity measured was the inter-vehicle time gap. The abstraction of the headway data although simple was long and tedious,however the most important advantage of using video tapes, over other automated methods of recording, is that a permanent record of the whole operation of the junction becomes available. Thus if any supplementary details are required they can be abstracted using the same videotape. The quantities abstracted included the size of all the accepted gaps of the circulating flow, the number of vehicles entering each gap from each lane of the entry, the total circulating flow and the composition of the flows. Table 3.1 includes the results of the analysis of the traffic volumes for

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