VTT Technical Research Centre of Finland investigated the safety effects of middle barriers on non-motorway highways in Finland. The results indicate that highway middle barriers greatly improve road safety and are particularly effective at reducing fatal accidents, with four in five such accidents prevented.
Interest in implementing highway middle barriers has increased given their associated positive safety effects. For instance, Sweden has significantly increased the use of such barriers within its highway network for this reason. Despite the very positive safety results from other countries, only few middle barrier roads have been built in Finland. This study was done to confirm if equally favourable safety effects have been achieved with them.
By using a before-and-after analysis and a maximum likelihood estimation, the development of road safety in terms of accident risk was investigated for Finnish non-motorway highways which had seen the implementation of a middle barrier. In addition, the current safety level of the highways was investigated and compared to similar highways lacking such barriers.
The above was also repeated to investigate the safety effects of highways separated by wide middle markings, an alternative to middle barriers. In addition, the current safety level of wide lane highways, another alternative, was investigated as well. It was not, however, possible to perform a before-and-after analysis for this road type. A generalised linear model was used to further compare current safety differences between the different road types.
Statistically significant results from the before-and-after study indicate that highway middle barriers are particularly effective at reducing fatal accidents and fatalities, with reductions of 80% and 83% respectively. Furthermore, a statistically non-significant reduction of 12% was found as the most likely effect for injury accidents on middle barrier highways. The most notable accident risk reductions after middle barrier implementation occurred for turning, rear-end, overtaking and head-on accidents. The increase in road safety was so substantial that it remained improved despite raised speed limits along certain stretches of highway.
In terms of current accident risk on Finnish roads, middle barrier highways feature the lowest risk of death and a generally lower risk of injury accidents and serious injury when compared to other highway types. Only motorways have a slightly lower risk of injury accidents and serious injury.
Modelling current accident risks on Finnish roads suggest the risk of death to increase by 40% by wide lane roads. The risk of fatal head-on accidents is almost double that of conventional highways, and the implementation of middle barriers on such roads is strongly recommended as one of the conclusions of the study.
The results for wide middle marking roads also show a risk of increased fatalities and injury accidents in general, but they lack statistical significance due to limited sample size. Wide middle markings seem to be associated with a decreased risk of head-on collisions. However, an increased risk of turning and rear-end accidents, as well as accidents involving cyclists were recorded on them.
Conclusion and implications
Middle barriers have a substantial positive effect for reducing fatal accidents and road fatalities, with four in five fatalities potentially prevented due to barrier construction. Furthermore, the barriers also effectively reduce injury accidents, with serious injuries especially well prevented. Risk of fatal accidents and fatalities on middle barrier highways were even slightly lower than that of motorways, which are considered to be among the safest road types. The alternatives to middle barriers did not perform as well in terms of road safety. The study recommends implementation of highway middle barriers on busy roads, especially those associated with frequent head-on collisions. Following the construction of middle barriers on non-motorway highways, fatal accident risks have either substantially reduced or such accidents have remained at zero.
The study was carried out by VTT as part of the Traffic Safety 2025 consortium.
Harri Peltola and Johannes Mesimäki (2019):
Safety effects of middle barriers on non-motorway highways in Finland (in Finnish)
VTT Technical Research Centre of Finland
VTT Technical Research Centre of Finland