The end of the year 2018 saw the launch of the Global Status Report on Road Traffic Safety by the World Health Organisation. The report noted a continued increase in deaths and injuries in road traffic crashes. According to this report, 1.35 million deaths have been reported in road traffic crashes in 2016 alone. This shows the enormity of the challenge faced by the safety community as the decade of safety action 2011-2020 draws to an end. We continue to face this problem in India too, as the number of deaths on Indian roads reported by the Ministry of Roads and Highways is 1.47 lakhs.
Many countries – mostly in Europe, Australia, North America and Japan have made significant progress in reducing injuries and deaths from road traffic crashes. These countries have implemented a number of different strategies to address the multiple factors which have been identified as contributing to road traffic crashes. There is a broad range of factors affecting road traffic crashes. These factors are usually related to traffic and road characteristics, drivers and other road users, vehicles, and environment. Traffic characteristics (such as traffic flow and speed) and road characteristics (such as road geometry and the quality of infrastructure) affect road traffic crashes.
Setting Speed Limits In Different Categories Of Roads
The current understanding of road safety science identifies the principal cause as to why people die and are seriously injured: the energy to which they are exposed to in a traffic crash, being excessive in relation to the energy that the human frame can withstand. Knowledge of energy and tolerance has to a great extent served as a basis for the development we have seen of the passive safety characteristics of vehicles and for the development of different protection systems such as child safety seats, helmets, seat belts, etc.
This knowledge has been responsible for setting speed limits in different categories of roads. Empirical studies show a very strong correlation between speed and probability of death and severe injuries. At an impact speed of 30km/h a pedestrian has less than 8% chance of death; however, an increase of speed by merely 20km/h (impact speed of 50km/h) and the same pedestrian has more than 80% probability of death. This understanding is the basis of fixing speed limits on urban arterials roads at 50 km/h, and other small roads at 30km/h and areas near school zones and markets where we expect more pedestrian traffic at less than 20 km/h.
Intercity highways which are designed for long distance traffic are designed for higher speeds. Since we do not expect the presence of pedestrians and bicycles on intercity highways, these roads are designed for 70-80km/h. The design of these roads – lane width, shoulder width and median designs are different from urban roads. Similarly, access controlled expressways are designed for 100km/h or more with different road design standards. Since in India pedestrians and other non-motorised vehicles are present on our highways, we have to evaluate the current road design standards to ensure the safety of all road users present on the roads.
Speed is an important factor affecting road accidents both in terms of accident occurrence and severity. It seems reasonably safe to assume that increased speed would mean that the accidents that have occurred would be more severe if other factors (e.g., environment and vehicle design) remain the same. Between speed and number of accidents, most of the studies suggest that increased speed is associated with more accidents or higher accident rates.
Understanding Road Designs
The second important principle of successful road safety strategy comes from the understanding of road user behaviour and road designs. Road users can be encouraged to observe appropriate speeds by changing the road designs. Wide straight roads can induce high-speed driving, whereas, narrow lanes, rough texture, and roundabouts force drivers to slow down. Road engineering approaches aimed at bringing the design of the road in accordance with the desired speeds of the vehicles plying on them constitute the guiding principles of Speed Management by Design or Traffic Calming.
Most successful traffic calming techniques are those which force drivers to slow down: speed humps, rumble strips, rough texture on roads etc. Around school zones or residential areas, the desired speed is less than 20km/h. This can be ensured by providing rough textured surfaces around this area. Residential streets need not have blacktop bituminous surface. If these textures are not possible, then we have to use frequent speed humps or rumble strips. Safety of bicyclists and pedestrians can be ensured on roads in urban areas (arterial roads) by having a separate lane for bicyclists and footpaths for pedestrians. For motorized traffic 3m, wide lanes are recommended for 50km/h speed.
At zebra crossings, flat top speed humps have to be made to ensure that motorists slow down before the zebra crossing. Safety at intersections increases with the use of roundabouts. Roundabout must be designed to force vehicles to deflect at the entry of the round-about and exit smoothly. Since the straight line of sight is disrupted at the roundabout, drivers are forced to slow down. In case of a crash, the angle of collision is much smaller. Therefore, the severity of injury reduces. Traffic calming has been recommended on highways also when it passes through habitations. Generally, a series of rumble strips and rough textured road surfaces ensure the safety of all road users in these segments.
The most important issue in ensuring safety on roads is the understanding that human beings are frail. Energy transferred to human beings at the time of a crash is related to speed. Therefore, safe roads are those which ensure appropriate speed by design. Safe roads are expected to induce safe behaviour by all road users, and also forgive those who make mistakes- so we need to design forgiving roads.
Geetam Tiwari is an Urban Transport planning expert and a Professor for Transport Planning at the Department of Civil Engineering, IIT Delhi.