Abstract: Traffic density provides an indication of the level of service being provided to the road users. When the length and speed of the vehicles in a traffic stream varies significantly, however, it has been, found that, the concept of occupancy, rather than density, is more appropriate to describe traffic concentration. This is because of the reason that occupancy takes into account the variation in the speed and length of vehicles in its measurement. The value of occupancy, however, changes with change in the detection-zone length. Also, the measure, occupancy is not appropriate under heterogeneous traffic conditions, as the traffic has no lane discipline and hence, it is necessary to consider the whole of the width of the road as single unit to analyze the traffic flow. Hence, a new concept named, “area-occupancy” is proposed. Simulation technique has been used to validate the concept of area-occupancy. To check for the validity of the concept, the occupancy and area-occupancy of a homogeneous traffic stream were related to the density of the stream and it was found that area-occupancy can be a substitute for occupancy. Then, the concept of area-occupancy was applied for heterogeneous traffic and a relationship was developed between area-occupancy and traffic stream speed. The developed relationship is found to be logical indicating the appropriateness of the area-occupancy concept for heterogeneous traffic conditions.

Key words: urban traffic, density measurement, heterogeneous traffic, occupancy, traffic flow, simulation models, traffic analysis

摘要： 交通流密度是衡量道路服务水平的指标之一. 当交通流中车辆长度和速度变化较大时，占有率则可以更好地反映交通流密度状况. 占有率的测定能够考虑到车辆的长度和速度变化，但是其值受到测量区域长度的影响，并且在混合交通情况下测量值缺乏准确性. 对于没有车道行驶规则的混合交通流，应当以整条路段为单位进行交通流分析. 因此本文提出了“区域占有率”的概念，且利用仿真技术验证其有效性. 对混合交通流条件下的占有率和区域占有率进行比较分析，区域占有率可以更合理地描述混合交通流的密度. 同时，得出混合交通条件下的区域占有率和交通流速度关系，证明了混合交通流条件下区域占有率提出的合理性和准确性.

关键词: 城市交通, 密度测定, 混合交通, 占有率, 交通流, 仿真模型, 交通量分析