Junction modelling is described within the framework of macroscopic traffic flow models. Given previous models, the focus is on the most important factor: first-in first-out (FIFO) effects. According to the number of lanes, current models assume either a perfectly FIFO traffic or a perfectly non-FIFO traffic. Although we assume a single-flow highway traffic model, the improvement takes into account lane changes close to merges and diverges. Thus the traffic is neither perfectly FIFO nor perfectly non-FIFO and so outflows at junctions depend considerably on junction topology, traffic distribution in lanes and driver behaviour. As a consequence, this article suggests a simple improvement of the description of merges and diverges which takes into account some of these factors. With respect to the previous models, the best improvement concerns the outflow forecasting on an uncongested exit of a diverge when the other exit is congested.
