To reduce air pollution peaks from highway traffic near residential areas, in the Flemish region of Belgium the authorities can impose speed limits on selected highway sections if defined conditions are given.
Background & ObjectivesIn Belgium, like other countries, parts of the highways are located near residential areas. The Flemish environmental administration identified 465 km of the highway net (in both directions) near housing areas where a temporal speed limit might reduce peak concentrations of air pollutants. This accounts for example for sections in the Brussels and Antwerp region.
ImplementationA speed limit of 90 km/h instead of 120 km/h will be imposed on these highways when the forecasted daily average PM10 concentrations are higher than 70 µg/m3 for two consecutive days. It applies for sections near residential areas, where the limit values for PM and NO2 are already exceeded and where a speed limit will improve traffic flow. The speed limits are on average introduced 2-3 times a year (between April 2007 and February 2009: 4 times). The restriction is maintained as long as the forecasted PM10 concentrations do not significantly decrease below 50 µg/m3.>On some sections, dynamic traffic management is already in place, on other sections the speed limit is currently indicated by persistent signposts.
ConclusionsThis measure is intended to reduce peak concentrations; it has only limited impact on the annual mean concentrations. The major conclusions of a study that investigated the effectiveness of the speed limit measure were:
- list item that the impact on PM2.5, PM10 and NO2 concentrations was limited.
- list item that the highest concentration decrease was found in the direct vicinity of the highways where the speed limit was in place.
- list item that the impact on “Elementary Carbon” (EC) or diesel soot concentrations (the component that probably has the greatest impact on human health) was much more important than on particulate matter and NO2.
- list item that excluding Heavy Duty Vehicles (HDV) or cars older than EURO 3 from these road sections during pollution events could have a more important impact on pollutant concentrations.
Traffic and demand management
16 Jul 2009
29 Aug 2014