Assessment of the effectiveness of active speed : warning signs - use of inductive loop data or empirical data?

The main emphasis of this paper so far has been on a description of the different approaches on how to assess the effectiveness of active speed warning signs (ASWS). The first result which can be concluded is that the best way to assess the effectiveness of an ASWS would be to conclude speed measurements before the installations of an ASWS and at the same spot after a certain period of time. A very good way of doing this would be the car-following method, as this generates a speed profile over a stretch of road instead of local speed data. If the assessment has to be done without any knowledge of the situation prior to the installation of the sign, this assessment is very difficult and most of the methods are time consuming and work intensive. The standard approach so far has been to analyse the inductive loop data and compare these two sets before and behind the location of the ASWS. Following intensive tests that have been carried out in the past, it can be said that this approach is not leading towards a realistic assessment of the ASWS. A more complex approach is the detailed empirical analysis. Compared with the analysis of the inductive loop data, both measurements are time consuming, here especially the analysis of the raw data, and therefore expensive. The approach which so far promised the best results is the car-following method. The data is fairly easy to gather and the processing of this data is quick. This method also gives detailed information about the speeding behaviour along the stretch of road. Typical characteristics of the general road layout can be deduced from the speed profiles. At the moment further research is being done on gathering the data of different ASWS, in order to gain more in-depth knowledge on how best to combine the different results. Hopefully, using these results, a more complex concept for assessing the effectiveness of ASWS, which integrates the different data sources, can be developed and put into practice. (A) For the covering abstract of the conference see ITRD no 207828. The reprints are also available at the web - http://www.vti.se/pdf/reports/K18APart1.pdf ; http://www.vti.se/pdf/reports/K18APart2.pdf and http://www.vti.se/pdf/reports/K18APart3.pdf.