What is Traffic Accident Study?
Traffic accident studies are systematic investigations conducted to find the reasons and causes behind accidents and to develop preventive measures through design, control, and enforcement. They form the evidence base for targeted safety improvements — from redesigning dangerous intersections to improving pavement friction, sight distance, or signal timing.
Accident Records Maintained
- Location Files: Maintain records of accident locations to identify high-accident points (black spots) for targeted intervention
- Spot Maps: Road network maps with accidents marked by spots, pins, or symbols — gives instant visual overview of accident clusters
- Condition Diagram: A scaled drawing showing all important physical conditions at the time and location of the accident
- Collision Diagram: Shows the approximate path of all vehicles and pedestrians involved in the accident, helping reconstruct the sequence of events
Coefficient of Restitution
In accident analysis, the coefficient of restitution (e) measures how much kinetic energy is conserved in a collision:
e = (V’_B − V’_A) / (V_A − V_B) = Velocity of separation / Velocity of approach
- Perfectly elastic collision: e = 1 (kinetic energy conserved)
- Perfectly plastic collision: e = 0 (vehicles stick together after impact)
For vehicles on the same path, collision is plastic (e = 0): V’_A = V’_B after collision. Momentum equation: m_A×V_A + m_B×V_B = (m_A + m_B)×V’
Analysis: Moving Vehicle Hits Parked Vehicle
The aim is to find the initial speed V_A1 of the moving vehicle before the accident. The analysis proceeds in three steps using skid mark measurements:
- From after-collision skid distance S_A2: 0 = V²_AB − 2μg(S_A2) → find V_AB
- From momentum conservation at collision: m_A×V_A2 = (m_A + m_B)×V_AB → find V_A2
- From pre-collision skid distance S_A1: V²_A2 = V²_A1 − 2μg(S_A1) → find V_A1
Key Traffic Engineering Points to Remember
- Kiss and ride = peripheral parking (passenger dropped off, vehicle parks separately)
- Fatal head-on accidents: mainly on single-lane or undivided roads
- Gravity model: used to simulate present and forecast future transportation demand
- Road-rail crossing: provide road over rail track (not road under rail)
- Viaduct: long bridge-like structure carrying a road or railway across a valley
- Lane requirements: Very low = 1 lane | up to 300 vph = 2 lanes | 300–600 = 3 lanes | 600–1500 = 4 lanes
- IRC 67-2012: signpost bands — 25 cm alternating black and white
- Vehicle light colour = yellow (best visibility in fog)
- Road lighting intensity measured in lux
- ISI recommends: 30 lux on important fast roads | 15 lux on other main roads | min/avg ratio = 0.4
- Single side lighting: up to 2-lane narrow roads | Staggered/central: wider roads >3 lanes