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# PDF (DX094490.pdf) - White Rose Etheses Online

PDF (DX094490.pdf) - White Rose Etheses Online

## 168 were assumed

168 were assumed constant. Therefore, the delays estimated by the model increased rapidly as the entry became saturated and entry capacity was exceeded. If the simulation period was increased the delays would increase indefinitely. From this point of view, the model has the same disadvantages as equil- ibrium state prediction formulae, and which are overcome by time-dependent methods, (see Chapter 2). Thus, the model is only suitable for studying delays suffered at conditions below and around capacity. The effect of turning proportion, flow and gap-acceptance parameters on delay has been studied for both flared and straight approaches. The relationship between delay and turning proportion is dealt with in this section, the next section covers the relationship between delay and the flow and gap-acceptance parameters. It should be noted that the results presented here are a selection of the values produced. The data relevant to this section are presented in figures 6.10 - 6.25. The first ei'ght, figures 6.10 - 6.17, present the data for the flared layout only, while figures 6.18 - 6.25 repeat the above data together with the data for the straight entry allowing direct comparisons to be made. From figures 6.10 - 6.17 an overall pattern of the variation of delay over the range of percent of left-turn used is emerging. Maximum delay is obtained for the combin- ation: left-turn = 0%/straight = 50%/right-turn = 50%. For each straigitproportion, delayisamaximum when left-turn = 0%. Delay decreases as the left-turn proportion increases, however, the graphs for the smaller straight proportions

169 exhibit a minimum average delay with 30 - 40% left-turn proportion; while for 50% straight proportion, there is an increase in average delay as the left-turn proportion approaches its 50% maximum value. The maximum delay at 0% left-turn is caused by the effective reduction of the entry from four to three lanes. The rise of delay at maximum left-turn is associated with the smallest straight through values used. At such conditions the effective number of lanes is reduced again as the high number of left-turners prevent the full use of certain positions at the stop line. Comparing the performance of flared and straight approaches (figures 6.18 - 6.25) the percentage increase in delay with straight entries has been determined for all data points. They are included in tables at the Appendix. From the eight cases presented, seven produce differences which on average are above 60%, i.e. the straight entries have cjn average delays exceeding the ones of flared entries by 60% or more. The averages are over all the turning proportion for each set of flow and gap-acceptance parameters. The only exception to the above relationship is the delays associated with the following parameters: Q 1 = 500 veh/hr, = 500 veh/hr, 2.80 sec, = 1.68 sec. In this case, although the average difference was only 10.6% the straight entry delays were consistently higher than the flared entry ones. The conclusion of this study is that conversion of straight to flared entries is associated with delay reductions of 40% or more in most cases for operation below

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