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PDF (DX094490.pdf) - White Rose Etheses Online

PDF (DX094490.pdf) - White Rose Etheses Online

1 j-J'. 1. The entering

1 j-J'. 1. The entering vehicles can turn right, left or follow a straight through direction. This would imply that the entry forms part of a roundabout with at least 4 arms. 2. Straight through vehicles can use both approach lanes, right turning only the offside, and left turning only the near- side lane. 3. At the flared part of the entry, straight through vehicles can use all lanes at the row before the stop line, but only the same lanes at the stop line, i.e. they can not use the nearside flared position. Right-turning vehicles can use only the offside lane. Left-turning vehicles can use only the extra lanes provided by the flare, i.e. they can use one lane at the row before the stop line and two lanes at the stop line. 4. Each vehicle has a preference in the order of lanes it can occupy at each row (if it is allowed to choose from more than one position). This preference order depends on what turning movement the vehicle is assigned. Right turning vehicles are not affected by this as they are allowed only at the offside lane. For straight through vehicles, it implies that when there is a high right-turning proportion they would use, mostly, the second lane along from the offside. Left-turning vehicles prefer to follow the nearside positions along the whole entry, both at the approach portion and at the flared part. 5. The distribution of circulating traffic was assumed to be shifted negative exponential. Some further aspects of the model are mentioned below: (a) The method of simulation was of the event scanning type. This resulted in more complex logic but permitted faster runs on the computer, especially for conditions of high circulating and demand flows.

153 (b) Three initial numbers for the pseudorandom fraction generating routine were used. This allowed the production of three completely different pseudorandom fractions sequences used to generate the circulating flow vehicles, the demand flow vehicles, and the assignment of turning movement to each demand flow vehicle. (c) Each demand flow vehicle was assumed to have arrived when it was generated. The time of arrival could be the time of its entry into the circulating flow had there not been any delay due to congestion. (d) The model does not take into account the delay of the vehicles remaining in the queue at the end of the simulation period. Thus, the average delay estimates refer to the delay of the vehicles which entered during the period of simulation. (e) The simulated period, during which measurements were taken, was 3600 sec. The complete simulated period was 3900 sec, which allowed 300 sec of initial transient time used to develop the demand and entry queue. (f) The nature of simulation does not allow the exact production of the requested traffic conditions. The circulating flow generated differs from the one input into the model. Similarly the input proportion of turning movements is different from the proportions as simulated. This aspect of the simulation is developed further in the following Chapter. It should be mentioned that validation of the modelled effect of the turning proportions on roundabout performance is very difficult as such observations in public road ides are almost impossible. (g) The program was written in FORTRAN IV - 1966 to be run on the PRIME-750 A computer of the University of Sheffield. The final version of the model, the simulation of 3900 sec of

The Archaeology of Medieval Europe - White Rose Research Online
See PDF version here. - Blue & White Online
See PDF version here - Blue & White Online
See PDF version here. - Blue & White Online
See PDF version here. - Blue & White Online
See PDF version here. - Blue & White Online
PDF (267549_VOL2.pdf) - White Rose Etheses Online