Run-off-road collisions are among the most serious types of accident on interurban roads. They occur when the driver loses control and the vehicle leaves its intended path, potentially colliding with changes in level, obstacles, structures or other objects located along the roadside.

A study carried out by Metalesa in collaboration with the University Research Institute on Traffic and Road Safety — INTRAS — at the Universitat de València has analysed the relationship between these accidents and Intelligent Transport Systems.

Its main conclusion is particularly significant: the ITS analysed could intervene in circumstances present in 49.5% of all run-off-road collisions. When the analysis is limited to serious and fatal accidents, the percentage rises to 59.7%.

This finding positions technology applied to infrastructure as a complement to conventional restraint systems.

A study based on interurban road accidents

The study analyses data recorded between 2017 and 2023 in the Spanish Directorate-General for Traffic’s ARENA system. Its methodology relates the circumstances recorded in accident reports to the systems included in the DGT’s ITS Plan.

The purpose is not simply to count accidents, but to determine which technologies can address the factors that occur most frequently or produce the most serious consequences.

Three criteria are used to establish these priorities:

  • Accident frequency: the number of accidents.
  • Injury severity: the number of casualties and the severity of their injuries.
  • Fatality rate: the proportion of people killed.

More than 37,000 accidents occur on interurban roads in Spain each year. Approximately 12,000 are run-off-road collisions, resulting in close to 500 deaths annually according to the data included in the study.

How can ITS respond to a run-off-road collision?

Intelligent Transport Systems combine sensors, radar, communication systems and signalling devices to detect risks and generate a response from the infrastructure itself.

Their role can begin before the vehicle leaves the carriageway. A system can, for example, detect inappropriate speed, adverse weather conditions or failure to maintain a safe following distance and activate a warning for the driver.

The technologies studied include:

  • Dynamic adaptation of speed limits.
  • Spot speed enforcement using fixed cameras.
  • Average-speed enforcement using section cameras.
  • Speed-limit violation warning systems.
  • Traffic guidance during adverse weather conditions.
  • Seat belt use detection.
  • Warnings when a safe following distance is not maintained.
  • Detection of animals or vulnerable road users on the carriageway.

These solutions do not all perform the same function. Some seek to prevent loss of control, while others reduce the severity of injuries or allow an impact to be reported quickly.

Speed as one of the main areas for intervention

Speed has a significant relationship with run-off-road collisions. The study indicates that, among accidents associated with the dynamic adaptation of speed limits because of adverse weather conditions, 66.5% were run-off-road collisions.

A strong relationship was also identified with speed-control systems using fixed cameras, average-speed cameras and speed-limit violation warnings. In these cases, run-off-road collisions accounted for 63.8% of accidents.

Dynamic adaptation makes it possible to change or reinforce the displayed limit according to the actual conditions on a section of road. It can be activated, for example, during heavy rain, fog or strong winds, or whenever the prevailing speed is unsuitable for the conditions.

Road signs therefore cease to provide a static message and instead respond to the specific condition of the road.

Seat belt detection and reducing accident severity

Not every ITS intervenes directly before a vehicle leaves the road. Some are intended to reduce the severity of the consequences.

The study analysed 34,613 accidents recorded between 2017 and 2023 in which a seat belt had not been worn. These accidents resulted in 48,388 casualties, including 2,982 fatalities and 8,593 people seriously injured.

In addition, 36.7% of the accidents associated with failure to wear a seat belt were run-off-road collisions.

Detection systems can identify non-compliance and generate a warning. In an accident, the seat belt remains essential for preventing occupants from striking the vehicle interior or being ejected.

From a conventional barrier to connected infrastructure

Prevention through ITS does not replace safety barriers, bridge parapets, terminals or crash cushions. These two levels of protection perform different but complementary functions.

Intelligent systems act before an accident by detecting and signalling the risk. Road restraint systems intervene once the vehicle has lost control, seeking to contain it, redirect it or reduce the energy of the impact.

Integrating both functions allows conventional equipment to become part of connected infrastructure. Sensors, radar and cameras can detect a dangerous situation, while road studs or variable-message signs communicate the warning to the driver. Data can also be sent to road operators, control centres or emergency services.

PLUG&META®: sensing and signalling from road equipment

PLUG&META® technology integrated into PlugSmart® Pro can transform restraint systems and other roadside equipment into intelligent devices.

The system can be installed on steel safety barriers, bridge parapets, concrete barriers, walls or tunnel linings. It operates through connections with radar, cameras, weather sensors and dynamic signalling equipment.

Situations it can detect or signal include:

  • Vehicles travelling at excessive speed.
  • Vehicles involved in accidents or breakdowns.
  • Wrong-way driving.
  • The presence of pedestrians, cyclists or animals.
  • Ice or reduced visibility.
  • Impacts against the restraint system.

When a risk is detected, the infrastructure can activate a light signal to warn approaching vehicles. If the accident cannot be prevented, the system can report the impact to the operator and send information to traffic platforms or control centres.

Prioritising ITS according to the risk on each road section

The study proposes a methodology for selecting ITS according to the accident frequency, injury severity and fatality rate associated with each circumstance.

This means implementation should not be treated as a uniform solution for the entire network. A section with run-off-road collisions linked to speed and weather conditions may require dynamic speed-limit adaptation and illuminated warnings. Another section with frequent wildlife activity may require specific sensors and alert systems.

Data analysis can identify which technology best responds to each scenario and concentrate action on the highest-risk locations.

Active road safety and vehicle restraint must work together

The figure of 59.7% represents the potential scope for ITS intervention in circumstances associated with serious and fatal run-off-road collisions. It does not mean that a single technology could automatically prevent all those accidents. It indicates that detection, warnings or control could perform a preventive role in a significant proportion of cases.

Combining ITS equipment and road restraint systems makes it possible to act at different stages:

  • Detect the risk in advance.
  • Warn the driver.
  • Adapt the signs or speed.
  • Contain the vehicle if it leaves the carriageway.
  • Detect the impact and report the incident.

Metalesa develops restraint systems and connected-infrastructure solutions designed to integrate these functions. The objective is to progress from a road that only responds to an impact towards one capable of detecting risk, communicating it and helping to prevent the accident.