The aim of this paper is to analyse the behaviour of the traffic flow at an area of merging traffic lanes where an application of the zip rule is expected, accoding to the law no. 361/2000 Sb. “o provozu na pozemních komunikacích”. Žabovřeská street, part of the VMO Brno, in the direction from Královopolské tunely to Hlinky interchange was chosen for observation and measuring. Observation, first-hand measurement, radars, and other available means were used for data collection. On the basis of data analysis, several suggestions for improvements are made. These are aimed at increasing the bottleneck capacity. One of the suggestions is tested in a simulation program Aimsun.