Local danger warnings

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'. Local warning systems use danger warning messages.

Impacts
The systems improve road safety by making the drivers more aware of incidents and other problems on the road section immediately ahead. Current evidence from accident studies indicates that roadside local warning systems reduce all injury crashes by -1 to -5% and all fatal crashes by slightly more.

Studies

Warned drivers reduced their speed in the first 10 seconds by about 18 %. Drivers in unequipped vehicles also benefit from the wireless local danger warning system, when the penetration rate of the system reaches 30 %.	Driver simulator tests with 41 test persons	Malone, K, Wilmink, I., van Noort, M, Klunder, G.	2007	IMPACT: Impact Assessment of In-vehicle Safety Systems. Proceedings of the 14th World Congress on ITS, 9-13 October 2007, Beijing, Peoples' Republic of China.
A sign warning about slippery road conditions reduced the mean speeds. In addition, the variable safety margin sign extended the headways and reduced mean speeds. The variable safety margin sign decreased the proportion of the drivers in queues with headways of less than 1.5 seconds by 28-38% during good road conditions and by 31-37% during slippery road conditions.	Field studies employing automated measurements of speeds and headways connected to road weather information	Rämä, P., Kulmala, R. & Heinonen, M.	1996	Muuttuvien kelivaroitusmerkkien vaikutus ajonopeuksiin, aikaväleihin ja kuljettajien käsityksiin (The effect of variable road condition warning signs). Helsinki. Finnish National Road Administration. Finnra reports 1/1996.
A Dutch fog warning system including a text warning ("fog") and dynamic speed limit VMS signs on a motorway, reduced speeds in fog by 8 to 10 km/h, although in extremely dense fog, the system had an adverse effect on speed. This was due to the too high "lowest possible speed limit" display in the VMS (60 km/h). A more uniform speed behaviour was obtained due to the introduction of the system.	Driving simulator studies	Hogema, J. H., van der Horst, R. & van Nifterick, W.[Author of the publication]	1996	Evaluation of an automatic fog-warning system. Traffic Engineering + Control, November 1996. pp. 629-632.