Abstract: To better understand the characteristics of traffic flow mixed by the cars and trucks on an up-slope, a cellular automata-based traffic flow model is proposed for single lane traffic considering the safe driving rules. The study reveals some new findings. Firstly, if a slope exits on a flat road, the traffic flow characteristics will change significantly. The previous decentralized congestion zone is changed for much short-intensive congestion, and focused on the slope and slope front. The slope impacts on traffic congestion significantly. A 40 m-long slope will increase nearly 10% increase congestion. Secondly, the trucks in the traffic flow can ease congestion in the low density case; however, the trucks’ impact on congestion is limited and even can be ignored for the high density case. Thirdly, no matter what the density and slope length are or whether a truck exists, the traffic congestion increases with the increment of the slope gradient, which indicates that reducing slope gradient can reduce traffic congestion. In addition, when the slope gradient is fixed, increasing slope length can also reduce traffic congestion.

Key words: car-truck heterogeneous traffic flow, slope, cellular automata, safe distance

摘要： 研究上坡道时小汽车和卡车组成的异质交通流的特点，将卡车分为重车和空车，使用的模型是一个更为精细的基于安全驾驶的元胞自动机（CA）模型，并通过计算机数值模拟分析了不同的坡度和坡道长度下异质交通流的特征。研究得出如下的结论：上坡道会明显改变交通流特征，交通流由之前分散的阻塞带变化为多个密集的短阻塞带，并且主要集中于坡道上和坡道前段，交通拥堵显著增加，40?m长的坡道就会增加近10%的拥堵；低密度情况下，卡车加入会在一定程度上缓解拥堵，重车缓解的程度更高，高密度情况下，卡车对于拥堵比例的影响较小；交通流的拥堵比例随着纵坡度的增大而增大，这说明减少纵坡度能够缓解拥堵；此外，当坡道纵坡度一定时，可以通过适当加大坡道长度而达到减缓拥堵的效果。

关键词: 小汽车-卡车异质交通流, 坡道, 元胞自动机, 安全距离