Dynamic traffic management

Description
Dynamic traffic management systems and local danger warnings are used to increase the safety and flow of traffic in cases of disturbance caused by incidents, congestion and adverse weather. The systems are operated automatically, semi-automatically or manually from traffic control centres based on fixed monitoring systems or mobile sensors (FCD etc.) on location. The systems employ Variable Message Signs or VMS to give the information to the drivers. Three categories of VMS exist based on the types of messages given: 'regulatory messages', 'danger warning messages' and 'informative messages'. The dynamic traffic management systems usually use regulatory messages, sometimes accompanied by danger warning and informative messages.

Impacts
The systems improve road safety by harmonising traffic flow and managing vehicle speeds according to the prevailing conditions. The impacts of the system depend on the quality of the traffic management system and the level of traffic volumes. Current evidence from accident studies indicates that the systems reduce all injury crashes by -5 to -20% and all fatal crashes by -10 to -25%. In addition, the systems improve the efficiency of the transport system, reduce congestion and increase driver comfort.

Studies

The safety of road users was influenced by the increased maximum permitted speed limit on free flow conditions and the fact that variable speed limits were used to lower speed limit in dense traffic conditions to obtain more harmonised traffic flow. The study indicated that variable speed limits decreased the number of injury accidents per million vehicle kilometres by 20%. However, the results of the study were not statistically significant. Variable speed limits were also found to improve travel times by 5% in dense traffic conditions. If queue situations are included in calculation, the reduction in travel time is 15%. Increase in the speed of vehicles was found to increase petrol consumption and carbon dioxide emissions. Socio-economic benefit-cost calculations were carried out for the Mölndal test site in which the socio-economical benefit-cost ratio was found to be more than 10. Of the four evaluated test sites two were estimated to be socio-economically profitable and in one case the cost were found to be larger than estimated benefits.	The safety effects were estimated on the basis of accident statistics of the test sites with a before-and-after study. The effects on traffic flow were studied by measuring vehicle speed and traffic counts. The environmental effects were calculated on the basis of changes in vehicle speed. Cost-benefit analysis was used to assess the socio-economical profitability.	Lind, G. and Lindkvist, A.	2009	Traffic controlled variable speed limits, Sweden. TEMPO Evaluation expert group, European Commission - DG TREN.
Variable speed limits reduced average speed of vehicles by 13-14 km/h during severe or very severe road surface conditions. The respect for the normal speed limit (120 km/h) has also increased.	A before-and-after study with speed measurements on a highway in Southwestern Sweden	Lind, G.	2007	Effects of traffic and weather controlled variable speed limits in Sweden. Proceedings of the 6th European Congress and Exhibition on Intelligent Transport Systems and Services, 18-20 June 2007, Aalborg, Denmark.
A variable speed limit system integrated with a slippery road warning system reduced injury accidents on a Finnish motorway by around 10 %.	Methods of the study: traffic speed measurements and telephone interviews. A reduction in speed was assumed to reduce the number of accidents.	Rämä, P.	2001	Effects of weather-controlled variable message signing on driver behaviour Technical Research Centre of Finland. VTT Publications 447
Route information and management systems employing VMS in Germany decreased the risk of road accidents by 15% and the risk of severe injury accidents by somewhat more, between 9 and 36 %. The impacts of the system depend on the quality of the traffic management system and the level of traffic volumes. On roads with high traffic volumes, the numbers of accidents were 22 – 64 % lower than before the implementation of the system. On roads with low or moderate volumes, the changes in accident numbers were statistically insignificant.	Evaluation of traffic management systems with accident data	Siegener, W., Träger, K., Martin, K. & Beck, T.	2000	Accident occurrence in the area of route information and management systems, allowing particularly for traffic load. IVT Ingenieurbüro für Verkehrstechnik GmbH. BAST.
Rear-end injury accidents have decreased as a result of queue warning systems on motorways whereas the number of rear-end accidents resulting in property damage only have increased.	A compilation of the results of accident studies	Elvik, R., Borger Mysen, A. & Vaa, T. .	1997	Trafikksikkerhetshåndbok (Traffic Safety Manual). Transportøkonomisk Institutt, Oslo. 704 p. ISBN 82-480-0027-3. ISSN 0802-0175.
Safety can be improved not only by just reacting swiftly to incidents but also by preventing them through harmonisation of the traffic flow via ramp control (or ramp metering), lane control, route diversion schemes, and in general traffic management.	Based on earlier accident studies	Bandmann, M. & Finsterer, H.	1997	Safety aspects of traffic management systems. Proceedings, 4th World Congress on Intelligent Transport Systems, 21-24 October, Berlin, Germany. ITS America, ERTICO & VERTIS.
Lane control has little effect on injury accidents. Ramp control is considerably more beneficial to safety, the accident reduction on equipped motorways being up to 10 % as such, and more than 15 % as a part of an integrated motorway management system	Literature review compiling results from accident studies.	Perrett, K. E. & Stevens, A.	1996	Review of the potential benefits of Road Transport Telematics. Transport Research Laboratory, TRL Report 220