Impact of Vehicle Speed on Road Safety

The speed of motor vehicles is universally recognized as the most important factor contributing to crashes, injuries, and fatalities on roads. Speed influences both the risk of a crash and the severity of its consequences.

Excess and Inappropriate Speed

Excess speed refers to a vehicle exceeding the prescribed speed limit, while inappropriate speed refers to a vehicle traveling at a speed unsuitable for the prevailing road and traffic conditions.

Modern Vehicles and Crash Risk

Modern cars, equipped with more efficient engines, can accelerate rapidly and reach high speeds within a short distance. Crash risk increases with speed, particularly at road junctions and during overtaking, as road users often underestimate the vehicle's speed and overestimate the distance of approaching vehicles.

In developing countries with mixed traffic and a high volume of vulnerable road users, increased speed has significantly contributed to the rising trend of fatalities on Indian roads.

Empirical Evidence

Studies show that an increase of 1 km/h in mean traffic speed typically results in:

• 3% increase in injury crashes
• 4–5% increase in fatal crashes

Speed has an exponentially detrimental effect on road safety: as speed increases, so do the number and severity of injuries.

Impact on Car Occupants and Pedestrians

• For car occupants, an increase in speed from 20 km/h to 100 km/h raises the probability of fatal injuries from nearly zero to almost 100%.
• The probability of serious injury for belted front-seat occupants is three times higher at 48 km/h and four times higher at 64 km/h, compared with the risk at 32 km/h.
• Pedestrians have a 90% chance of surviving car crashes at 30 km/h or below, but less than a 50% chance at 45 km/h or above.
• The probability of pedestrian fatalities rises eightfold when impact speed increases from 30 km/h to 50 km/h.

Older pedestrians are even more physically vulnerable as vehicle speed increases.

Speeding as a Cause of Severe Crashes

• Drivers have less time to react and avoid mishaps, and stopping distances increase, raising both the likelihood and severity of crashes.
• Vehicle structures may be unable to withstand crash forces, leading to serious injuries for occupants.
• The protective effectiveness of restraint systems, such as airbags and seat belts, as well as roadside safety features like barriers and bridge rails, may be compromised.
• Higher speeds cause increased tire wear, higher operating temperatures, longer stopping distances, and increased brake wear.
• At faster speeds, drivers’ ability to accurately see and judge distances is impaired.

Conclusion

Controlling vehicle speed is critical to reducing both the frequency and severity of road crashes, protecting occupants and vulnerable road users alike.