Extending the Cell Transmission Model to Multiple Lanes and Lane-Changing

Macroscopic or flow-based dynamic traffic assignment (DTA) models normally treat traffic in each direction on a roadway as a single lane and, since they do not consider multiple lanes, they can not consider lane-changing behaviour. To investigate how the results may be affected by explicitly considering lanes and lane changing, we consider a road link that consists of two adjacent homogeneous lanes. We assume that traffic entering each lane already knows in which lane it wishes to exit at the end of the link, whether it wishes to exit in the same lane or in the other lane. We model the traffic flows in each lane using a cell transmission model but adapt it to allow for traffic moving from cells in one lane to cells in the other lane. The CTM is used because it handles the modelling of queues and their spillback in an intuitive and widely accepted manner, and our extensions of it allow congestion in one lane to spill back into adjacent lanes. In particular, we investigate how lane-changing and congestion are affected by varying the assumptions concerning two key behavioural parameters, namely the locations at which drivers wish to change lanes and the vehicle spacing needed for lane changing (gap acceptance) as compared to the spacing needed when staying in the same lane (car following). We conclude that there are many situations where modelling a link as a single lane will give a poor approximation to the underlying multi-lane behaviour, or be unable to capture issues of interest, and for those situations multi-lane modelling is appropriate.