Excessive speed is still one of the main factors in traffic accidents. Numerous measures can be used nowadays to improve safety on roads. One main issue is reducing speed to a safe level. In recent years, new technologies have been used to this end. One of these are active speed warning signs (ASWS), which are activated by drivers whose speed exceeds a pre-set threshold. By means of a variable message sign, the drivers are made aware of their speed and the danger ahead. Typical locations for ASWS are town entrances and dangerous curves. Earlier this year, the "Instructions for Planning and Use of Active Speed Warning Signs" were introduced and published by the German Research Institute. In these instructions, a method is described on how to assess the effectiveness of an ASWS with the use of inductive loop data, as this data is normally available. The research presented here aims to analyze the effectiveness of an ASWS both with inductive loop data and with data especially gathered in empirical measurements.