eSafety Compendium

Dynamic traffic management and local danger warningsIncident warnings are provided by roadside VMS or beacons, and via radio and cellularinformation services. Studies usually show accident reductions on the IWS (Incident WarningSystem) equipped motor way sections. The whole range of the effect on the total number ofinjury accidents is from –35 per cent to + 9 per cent, where the largest reductions may includebias caused by the regression-to-the-mean effect. The effects are more beneficial on secondaryaccidents (Kulmala, Fránzen & Dryselius, 1995). According to Elvik et al. (1997), rear-end injuryaccidents have decreased as a result of queue warning systems on motorways whereas thenumber of rear-end accidents resulting in property damage only have increased. Japanese fieldtests (Makino 2004) of a local obstacle and congestion warning VMS system on a motorwayindicated a 45% reduction in accidents after the VMS was installed, but the effect is probablybiased due to the regression-to-the-mean effect.Safety can be improved not only by just reacting swiftly to incidents but also by preventing themthrough harmonisation of the traffic flow. This can be accomplished by ramp control (or rampmetering), lane control, route diversion schemes, and in general traffic management. Safety is alsoexpected to be improved as a result of replacement of manual toll collection with automatictolling on motorways due to the elimination of traffic channelling at toll plazas as well as of thepossible queues and unnecessary stops (Bandmann & Finsterer, 1997).Lane control has little effect on injury accidents (Perrett & Stevens, 1996 and Elvik et al., 1997).Ramp control is considerably more beneficial to safety, the accident reduction on equippedmotorways being up to 10 % as such, and more than 15 % as a part of an integrated motorwaymanagement system (Federal Highway Administration, 1997a; Perrett & Stevens, 1996).Route diversion schemes are beneficial to safety only when the diversion does not increaseexposure (driving distance) too much and does not divert traffic to roads with higher accidentrisk. Unfortunately, this is very seldom the case. The opposite case is shown by for exampleLashermes and Zerguini (1997).Route information and management systems employing VMS in Germany decreased the risk ofroad accidents by 15% and the risk of severe injury accidents by somewhat more, between 9 and36 %. The impacts of the system depend on the quality of the traffic management system and thelevel 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 moderatevolumes, the changes in accident numbers were statistically insignificant. (Siegener et al 2000)Page 367 of 490