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信号周期是交通控制的主要参数之一，也是影响交叉口公交车辆延误的主要因素.本文提出考虑在线优先需求的离线信号周期优化结构模型，其最优周期由离线基本周期和在线增量两部分构成.离线基本模型以加权车均延误为目标，探讨公交权重的影响因素及其与公交运行效益、社会车流运行效益的关系；在线增量计算以在线优先策略提供可实施空间为目标.分析一个四相位信号控制交叉口，对所提模型进行仿真验证.结果表明，公交车均延误最小的最优周期和社会车流车均延误最小的最优周期并不重叠，在一定的公交权重下，模型能够求得二者加权最优解.适当的在线增量引入，能够进一步降低公交车辆延误，且不会对非优先车流产生较大影响.

Optimal Offline Cycle Length Model Based on Online Bus Priority Demand

Cycle is one of the most important parameters of traffic control system which has many effects on the delay of buses. The basic requirement of bus signal priority is to decrease bus delay at intersections. First, the optimal cycle length model under the condition of bus signal priority is developed by giving different weight to vehicles and buses. Then, a four phase signal controlled intersection which has an exclusive bus lane is adopted to validate the optimal cycle length model and analyze the effects of different weight. The results show that the optimal cycle for buses and vehicles is not equal. And the weighted optimal cycle length model can make a trade off between buses and vehicles. Finally, the appropriate on line increment of cycle can further reduce the delay of buses and would not affect the non priority vehicles.