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PDF (DX094490.pdf) - White Rose Etheses Online

PDF (DX094490.pdf) - White Rose Etheses Online

Introduction 39 The

Introduction 39 The development of a simulation model does not require the collection of large number of data. In the present study, data were required on two occasions. The first one was the validation of model SI'4C developed previously, (see Chapter 5); the second was to provide an indication of the way entering vehicles position themselves at the available lanes, taking into account their turning movement. Both sets of data observations were not extensive and were conducted over a brief period of time, (generally 30 minutes). 3.2 The Collection of Gap-Acceptance Data Data were required to validate the simulation program developed previously, which formed the basis of the present work. Program SINC uses constant values for the critical gap and the move-up time to produce an estimate of the capacity associated with each circulating flow value. The observations, at this stage, were required to provide values for the circul- ating and entering flows, and for the gap-acceptance parameters. Therefore, the sites had to fulfil certain criteria: at least one of the entries had to operate at capacity for a considerable length of time; a suitable vantage point had to be available for positioning the video camera andrecorder used for data recording; no pedestrian crossings or other forms of traffic control should be affecting the approach to the entry; and the entry should have more than one lane. Preliminary investigations showed that very few sites, fulfilling all the above criteria, were available in "4

40 Sheffield. It was observed that, in general, each lane of the entries behaved in a different way. This was particularly true for the nearside lane at the entry position. It was decided to treat each lane of the entries separately, rather than assume each entry as a uniform entity. The peculiarities of each site are discussed below, in greater detail. sidered acceptable: Three sites near the centre of Sheffield were con- (1) Moore Street Roundabout, (2) Castle Square Roundabout, and (3) Park Square Roundabout. Moore Street Roundabout (ligure 3.1) is at the junction of the Inner Ring Road, Moore Street and Ecciesall Road. During the morning peak period heavy delays and long queues occur at Ecciesall Road entry. This entry carries traffic approaching the city centre, while large volume of traffic uses the Inner Ring Road, resulting in the heavy delays and long queues along Ecciesall Road. The entry has four lanes at the stop line; the nearside one is used by a large number of buses, while a bus stop is positioned near the stop line. Thus, the nearside lane is not continuously saturated. Therefore, it was decided not to take into account the data from that lane. Similarly lane 2 was not saturated for long enough periods for the data related to it to be suitable for capacity calculations. Castle Square Roundabout (fig. 3.2) is very near the city centre, it forms the junction of Arundel Gate, High Street, Angel Street and Commercial Street. During the morning peak period heavy flows are observed along Arundel Gate and from Commercial Street towards Angel Street. The flow entering from Commercial Street forms the majority of the circulating

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