Testing visual angle car following models using different sets of data

The basic assumption in visual angle car following models is that the following distance between successive vehicles is a function of the object (i.e. leading vehicle) width. This paper examines the validity of this assumption using two types of data. Published real traffic data from instrumented vehicles in the USA and Germany have been used to check the ability of these models to replicate real traffic movements when both leading and following vehicles are “small cars”. Also, another type of data was used based on over 4 million cases of individual vehicles which have been abstracted from inductive loop detectors installed on the M25 and the M42 motorways in the UK. The data was then filtered and analysed to examine the following distance according to the type of the leader (i.e. Car or Heavy Goods Vehicle - HGV). The results show that while the visual angle car following models can successfully replicate real traffic movements based on the instrumented vehicles data, the assumption of leaving larger following distance if the leader is an HGV is found to be not the case for the majority of UK drivers. This will have a negative impact on the use of visual angle car following models to represent real traffic behaviour.