- 2076 Chaitra · 8 marks
Vehicular characteristics influencing traffic performance
Short answer
Static characteristics include width, height, length, wheelbase, ground clearance, turning radius, weight and axle load, and eye height, which fix lane width, clearance, curve widening and pavement thickness. Dynamic characteristics include power, acceleration, braking, resistances, stability, headlight range, and vehicle mix expressed in PCU values.
Explain different vehicular characteristics that influence traffic performance.
Vehicular characteristics are the properties of vehicles that affect geometric design, traffic flow, safety and pavement design. They are classed as static and dynamic.
Static characteristics
| Characteristic | Typical value | Effect on road design |
|---|---|---|
| Width | 2.5 m (trucks, buses) | Lane width (3.5 m rural, 3.0-3.25 m urban), parking bay width |
| Height | up to 4.75 m (IRC) | Vertical clearance under bridges and tunnels (5.5 m minimum, IRC:5) |
| Length | 11-12 m rigid, up to 18 m semi-trailer | Parking bays, curve widening, kerb radius, passing and storage lanes |
| Wheel base and overhang | 6-7 m (truck) | Extra widening on curves, minimum turning radius, tail swing |
| Ground clearance | 0.2-0.3 m | Hump, drain and vertical-curve design |
| Turning radius | 12-14 m (truck) | Minimum intersection radius, island and median-opening design |
| Weight and axle load | 10.2 t legal single axle; 8.16 t standard axle in IRC:37 | Pavement thickness, bridge loading (IRC:6), width of bridge |
| Eye and object height | driver eye 1.2 m, object 0.15 m (IRC:SP:23) | Sight distance at crests |
Examples: the 2.5 m width and 11 m length of a bus fix the minimum bay size; the 4.75 m height fixes bridge clearance; the large turning radius of trucks fixes the radius of intersection corners; the axle load fixes pavement thickness.
Dynamic characteristics
- Power and performance: engine power, tractive effort and weight-to-power ratio decide acceleration, gradient ability and the need for climbing lanes.
- Speed and acceleration: the typical range of speeds and accelerations fixes overtaking sight distance, the length of acceleration/deceleration lanes and signal timings.
- Braking and braking efficiency: deceleration depends on tyre-pavement friction (f about 0.35-0.40); it fixes stopping sight distance.
- Resistances: air, rolling, grade and curve resistance decide fuel use and the speed on gradients.
- Turning and stability: centrifugal force limits speed on curves, so superelevation and an adequate radius are provided; vehicles with a high centre of gravity may overturn.
- Headlight range and visibility: fix night sight distance and vertical-curve length.
- Vehicle mix: the share of heavy vehicles sets the PCU factors (IRC:64-1990 for rural roads: car 1.0, bus/truck 3.0, motor cycle 0.5, bicycle 0.5, cycle rickshaw 2.0, horse-drawn vehicle 4.0, bullock cart 8.0).
Other characteristics
- Vehicle composition and PCU: the traffic mix is converted to passenger car units (IRC:64 rural, IRC:106 urban) for capacity and signal design.
- Visibility from the vehicle: the driver's eye height and headlight height decide sight distances.
✓ Answer checked by Claude Opus 5.5 (high effort)
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