The negative effects of homogeneous traffic on merging sections

Homogeneous traffic flows are believed to be better in absorbing disturbances, raise capacity and stimulate traffic safety. Measures to make traffic more homogeneous are therefore often taken to increase capacity. This paper shows that the ability of a traffic flow to deal with traffic coming from an on-ramp reduces when the through flow becomes more homogeneous. A motorway was modelled in the micro-simulation model AIMSUN2 and traffic of different levels of homogeneity was confronted with on-ramp traffic. The research confirms the hypothesis that the less homogeneous traffic is, the more acceptable gaps for merging vehicles become available. So homogeneity measures should always be combined with onramp metering which both recognises and acts upon the new distribution of critical gaps in the flow.