In the European Union, single vehicles are involved in up to 45% of fatal road accidents, which can be primarily classified as run-off-road accidents, where the vehicle leaves the road and enters the roadside.
Now, a number of countries are working on the concept of ‘forgiving roadside’ to avoid accidents of errant vehicles with potential hazards or to minimise consequences of crash. The concept of forgiving highways (wider and straighter) emerged from the 1966 National Highway Safety hearings in the US. Many a times, there is dichotomy between adopting self-explaining roads as against forgiving roads.
The forgiving roadside minimizes the consequences of an accident caused by driving errors, vehicle malfunctions, or poor roadway conditions whereas self-explaining road is designed to prevent driving errors. Forgiving roads address the provision on roadside safety treatments that help bring errant vehicles back into the lane to reduce injury and fatal run-off-road accidents. If the vehicle meets with a road element, the next stage of action is minimising the severity of the crash. In other words, the roadside should be planned and designed to forgive error of a driver by minimizing the severity of run-off-road accidents.
Even the placement of Rolled-In Continuous Shoulder rumble has a positive effect on the reduction of road accidents to the extent of 13 %, according to the study ‘In the Safety Evaluation of Rumble Strips Installed on Freeways’ by FHWA, the US in 1999. The Self-Explaining Road, on the other hand, is designed in such way that road users immediately perceive how to drive with their expectations and perceptions of the road built on a clear and recognizable standardised design, but it does not address the mistakes caused by errant drivers.
Conference of European Directors of Roads (CEDR) has identified the design of forgiving roads as one of the top priorities in its Strategic Plan 2009-2013. In recent years, many studies were conducted with a view to evolve guidelines as well as establish design standards for forgiving road sides worldwide. Additionally, considerable numbers of lives are lost in collisions with lighting columns and other road equipment. Impact tests after the occurrence of road accidents due to hitting a fixed object can be ranked into performance classes: (i) energy absorption level; (ii) impact speed; and (iii) vehicle occupant safety level.
Accidents with passively safe structures including impact on the lighting columns and other support structures have demonstrated several times that the system works. Not all locations are suitable for the installation of a passively safe support. It is imperative to build on the concept that the people will make mistakes but the risks involved due to design of forgiving roads should have minimal effects on casualty/injury.
In most countries, the major strategy is to ensure a clear zone of a certain width that includes recovery zone allowing drivers to regain control over their vehicles and return to the lane or stop with the removal of obstacles envisaged during the planning phase for a new road in particular. A recovery zone is an unobstructed, relatively flat or gently sloping area to reduce accidents - important because when travelling off the road, the vehicle was still controllable in 56% of the cases as seen in America.
Clear zone width is a function of the posted speed, shoulder, recoverable and non-recoverable side slope, and traffic volume. However, some guidelines also include curve radii in their calculations. There is no need to provide median barriers if width of the median exceeds more 15m that is a part of forgiving road as per the Ontario Roadside Safety Manual.