The Impact of Trajectory Speed Control

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Trajectory speed control measures a vehicle’s travel time between two fixed points along a road, and infers its average speed from those observations. In this impact assessment, we studied the trajectory speed control setup along the A10/E40 in Belgium, between Brussels and Ghent. For the study, we used traffic data that was collected by the Flemish Traffic Centre in their data warehouse. In contrast to previous studies of trajectory speed control, the data here is quite detailed as it contains all 5-minute intervals for over 2 years. In addition, we also analysed traffic safety by means of accident data we received, courtesy of the Belgian Police.

Our main conclusions are that there is no impact on the capacity of the road at that location. There is a noticeable drop of around 4% in the speeds of cars and vans. More spectacularly, there is a drop of some 25% to 30% in the speed deviations of these vehicles, implying that the traffic stream is more stable due to the trajectory speed control. We also observed a positive impact on traffic safety, with the number of accidents dropping by some 15% (implying 23% less vehicles involved). Furthermore, we estimate a drop of around 29% in light offenders, and an even more pronounced drop of around 78% in heavy offenders. Given the cost for initial deployment and direct benefits from fines, the measure seems to have an initial benefit-cost ratio of approximately 9.7:1 for the first year. Thereafter, the benefit-cost ratio is higher as there are only maintenance costs involved for subsequent years.

Trajectory speed control is a useful measure to reduce the number of accidents without hampering traffic flow. Given the nature of this measure, we also encourage its use on non-motorways, such as city ring roads and N-roads. Note that single-location flashing cameras are still very useful, for example in built-up areas. We believe good policy is made by a fruitful combination of both approaches to enforcement, coupled with the sensitisation of road users, explaining the motivation and effects of these measures.

Period

2014

Client

ITS.be

Partner

/

Our team

Lars Akkermans, Sven Maerivoet
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