The traffic situation and road conditions may lower the speed limit on roads – do you know how the variable speed limit signs work?

The variable speed limit signs on roads react to the prevailing weather and traffic situation. They, for example, help to alleviate congestion ahead, contribute to smooth running of logistics and affect transport emissions. There are hundreds of electronically operating variable speed limit signs posted along the main roads in Finland. Do you know how their technology works and from where speed limits are controlled?

Road transport accounts for about 63 per cent of goods traffic and 90 per cent of passenger traffic. Tens of thousands of vehicles drive on the Finnish roads every day. Many things must fall into place in the background to ensure that the roads can carry this massive vehicle traffic as safely and smoothly as possible. Variable speed limit signs are part of the roadside technology used in Finland aimed at ensuring the safety and smooth running of road traffic.

“We control the variable speed limit signs from Fintraffic’s road traffic centres. From these centres, we lower the speed limits of high-volume road sections if the traffic situation or road conditions so require. The need to change the speed limit may derive from factors such as deteriorated driving conditions, accidents, obstacles or animals on the road or changes in the speed of traffic flow. Sometimes speeds are lowered proactively even before traffic congestion occurs. Lowering the speed limit also supports safety in accident situations and during road repair and maintenance work. The reason for the lowered speed limit may not always be visible to the driver on the road, but the limit must still be complied with,” says Kari Tarkki, Head of Fintraffic’s Road Traffic Management Centre.

Variable speed limit signs are controlled from Fintraffic’s road traffic centres

Securing the safety of transport on Finnish roads relies strongly on using technology and digitalisation, the daily interaction of thousands of devices. The first variable speed limit signs were introduced in Finland at the beginning of the 1990s. Due to the high construction and maintenance costs and the rapidly ageing technology, they are now only implemented on sites where they affect traffic safety and flow of traffic the most. 

“As a rule, such sites include busy main and regional roads and incoming routes of large cities where the risk of accidents is particularly high or major congestion occurs. For the sake of consistency, variable speed limit signs are mainly erected on longer road sections using several signs in succession,” says Tarkki.

Variable speed limit signs are operated from Fintraffic’s road traffic centres. Thanks to artificial intelligence-based automatic control, intelligent traffic control systems propose measures based on the observations made by devices placed on traffic sites.

“In practice, this means that, based on the data produced by the equipment on site, AI automatically proposes what would be the appropriate speed limit in each situation. The control system is supervised and controlled by a traffic operator on duty at the road traffic centre. They verify and accept or reject the proposal made by the system,” Tarkki says.