Any situation that causes traffic to stop or slow down creates cost for society, both in terms of lost time for the road users and increased CO2 emissions. Trafik Stockholm, a traffic management centre for Stockholm collectively run by STA, Stockholm city and Nacka municipality therefore have the responsibility to facilitate the removal of such situations. One of the means by which they do that is by sending out road assistance vehicles (RAVs) to help clearing these situations. In order to do so effectively there is a need to know the effect of emergency lights on the time it takes for the RAV to reach its destination. This thesis thus examines how the emergency lights affect the speed at which the RAVs can travel by comparing the actual speed at which the RAVs have travelled using emergency lights to the mean speed of traffic on the same highway at the same time. It is concluded that there might be a significant effect, but further studies are necessary to prove this statistically.