The speed of motor vehicles is universally agreed to be the most important factor contributing to crash, injuries and fatalities on roads. Speed influences both crash risk and crash consequence.
Excess speed refers to a vehicle exceeding the prescribed speed limit and inappropriate speed refers to a vehicle traveling at a speed unsuitable for the prevailing road and traffic conditions.
Modern cars fitted with more efficient engines have very high acceleration and can achieve high speeds within a very short time and distance. Crash risk increases as speed increases especially at road junctions and while overtaking - as road users underestimate this speed and overestimate the distance of an approaching vehicle.
Further, in developing countries with a mixed traffic and high volume of vulnerable road users, increased speed has significantly contributed to an increasing trend of fatalities on Indian roads.
Empirical evidence from speed studies has shown that an increase of one KM per hour in mean traffic speed typically results in a 3% increase in the incidence of injury crashes or an increase of 4% to 5% for fatal crashes.
Speed has an exponentially detrimental effect on safety. As speed increase so do the number and severity of injuries. Studies show that the higher the impact speed the greater the likelihood of serious and fatal injuries.
- For car occupant, an increase in speed from 20 Kms to 100 Kms, the probability of fatal injuries increases from close to zero to almost 100%.
- The probability of serious injury for belted front seat occupants is three times as great at 48 km/hr and four times as great at 64 km/hr, compared with the risk at 32 km/hr.
- Pedestrians have a 90% chance of surviving car crashes at 30 km/hr or below, but less than a 50% chance of surviving impacts at 45 km/hr or above.
- The probability of pedestrians being killed rises by a factor of 8 as the impact speed of the car increases from 30 km/hr to 50 km/hr.
Older pedestrians are even more physically vulnerable as speed increases.
SPEEDING CAN BE A CAUSE OF SEVERE CRASH
- Drivers get lesser time to avoid mishap and the stopping distance lengthens which increases both the likelihood of crashing and the severity of the crashes.
- The vehicle structure is rendered incapable of withstanding the force of the crash which results in serious injury to the occupants.
- The protection capability of restraint systems such as airbags and safety belts and roadside hardware and safety features such as barriers and bridge rails become nullified.
- Vehicles become prone to increased tire tread wear, rise in tire weakening operation temperature, longer stopping distances and increased brake wear.
- At faster speeds the driver's ability to accurately see and judge the distances get compromised