A study published by Väylävirasto (The Finnish Transport Infrastructure Agency) suggests that motorists are more likely to speed in tunnels. Väylävirasto is responsible for developing and maintaining the state-owned road network, the railways and the waterways in Finland.

It is a very elaborate and interesting study. It is available on the website of Väylävirasto for anybody to read and benefit. I will try to give a summary of the report below by mostly using its abstract, but if you are involved in tunnel design, operation, safety, I would highly recommend you to get an English language copy (get it translated at your organization to English after getting Väylävirasto permission).

Reading from the abstract of the study (in Finnish), the researchers have "examined the frequency of speeding in road tunnels, road safety in tunnels, the safety impact of speed levels, and methods to curb speed levels".

The report writes that There are 25 road tunnels in Finland and a number of urban tunnels. According to statistics, there have been a total of 84 accidents inside the tunnels and 12 in the tunnel area outside. Data for 2017 were compiled from thirteen geographical fourteen and from fourteen tunnels in 2018 and 2019.

According to measurements carried out during the study, the share of drivers speeding in urban traffic tunnels is about 80% compared to the more than 50% speeding in motorway tunnels. A total of 15% of drivers are speeding at speeds of more than 10–15 km/h over the speed limit. Daily, there are cases in tunnels where the speed of the driver is more than one and a half times the speed limit."

More speeding but fewer accidents in tunnel, though accidents in tunnels are more serious

The study refers to earlier studies on speeding like the one in 2019 in the Muurla-Lohja tunnel where the speed limit is 100 km/h. Weekly measurements had recorded more than 20 motorists driving at 170 km/h and almost 600 at 140 km/h.

Study says, "There are fewer accidents per driven kilometre in tunnels compared to open sections of road, but an accident in a tunnel is more likely to lead to serious consequences than an accident on an open section. In addition to personal injuries, consideration must be given to the frequency and duration of interruptions in tunnel traffic, the impact of interruptions on the nearby road network, and the added costs of traffic and transport as well as any potential material damage of a larger scope. High speeds increase the risks of personal injury and damage to structures in the event of an accident. "

Accidents. Where in the tunnel?

Report also refers to a tunnel study from Norway where while looking at accidents, researches have also looked into where the accidents happened in the tunnels. According to study, the accidents are more likely to happen in the 50 meters before the mouth of the tunnel. As you go deep into the tunnel, the risk of having accidents decreases, but the severity of the accidents increases. The collisions were more common inside bi-directional tunnels than at mouths. Another study says that the drivers are more likely to drive close to the centre line, away from the wall.

Measures against the speeding in tunnels

Study lists various anti-speeding measures, including automatic speed control methods (spot, average etc), camera usage, using patterns, lighting along with their advantages, disadvantages as well as the legal aspects involved.

Study reads, "Automatic speed monitoring affects the average speeds of traffic flow and especially the highest speeds of speeding. In Finland, the resources of automated speed monitoring have been directed at road sections where there have already been more accidents than on average. In road tunnels, the preventive use of speed control measures is justified from the viewpoint of reflective effects from interruptions and the property management of Finnish Transport Infrastructure Agency. With regard to the automatic monitoring of tunnels, one factor is also the greater maintenance needs compared to the rest of the road network, as well as safety during maintenance work. For this reason, automatic monitoring of tunnels is also recommended for testing in motorway tunnels.

The impacts of average speed monitoring have been found to be better in terms of road engineering and to have a broader scope than the point-to-point monitoring currently in use. However, average speed monitoring requires technical development work and administrative changes to existing processes, and it is also costly with regard to a single tunnel. In the near future, it will be possible to achieve safety impacts more quickly by extending the current point-to-point speed monitoring. The assessment of the conditions for implementing average speed monitoring should, however, be continued over a longer period of time. Average speed monitoring would be especially suitable for long tunnel and road sections, which would also even out cost differences compared to point-to-point monitoring.

With regard to other speed monitoring measures suited for the road environment, wide centre-line markings have been found to have a clear effect in reducing driving speeds. In the future, it will be advisable to examine the application of visual speed control measures in tunnel conditions in more detail."

https://julkaisut.vayla.fi/pdf12/vj_2021-30_maantietunneleissa_ajettavien_web.pdf

photo: Karnainen Road Tunnel, Finland by kallerna, CC BY-SA 4.0 via Wikimedia Commons