Four aspects of the pavement surface are important for safe and comfortable driving;

  • friction between the wheels and the surface of the sidewall,
  • unevenness of the road surface,
  • the light reflection characteristics of the top of the pavement surface, and
  • Drainage for water.


The friction between the wheel and the sidewall surface is an important factor in the design of horizontal curves and thus the safe operating speed. In addition, it also affects the acceleration and deceleration ability of vehicles. Lack of sufficient friction can cause vehicles to slip or slip.

  • Skiding occurs when the path traveled along the road surface exceeds the circumferential speed of the wheels due to friction
  • Slip occurs when the wheel spins more than the longitudinal speed along the road.

The various factors affecting friction are:

  • type of pavement (eg bituminous, concrete or gravel),
  • pavement conditions (dry or wet, hot or cold, etc.),
  • tire condition (new or old), and
  • Vehicle speed and load.

The force of friction that develops between the wheel and the sidewall is the weight multiplied by a factor called the coefficient of friction and is represented as F. choice of value F This is a very complex issue as it depends on many variables. The IRC suggests the coefficient of longitudinal friction: 0.35-0.4 Based on the speed and coefficient of lateral friction 0.15, The former is useful in sight distance calculation and the latter is useful in horizontal curve design.


It is always desirable to have a uniform surface, but it is rarely possible to do so. Even if the road is constructed with high quality pavers, it is possible to develop unevenness due to pavement failure. The disparity affects vehicle operating cost, speed, ride comfort, safety, fuel consumption and wear and tear of tires.

inequality index There is a measure of unevenness which is the cumulative measure of the vertical fluctuation of the pavement surface recorded per unit horizontal length of the road.

An unevenness index value of less than 1500 mm/km is considered good, a value of less than 2500 mm/km is satisfactory up to a speed of 100 km/h and a value of more than 3200 mm/km is considered good for 55 km/h. Also considered uncomfortable.

3.light reflection

  • White roads have good visibility at night, but glare during the day.
  • No glare during the day on black roads, but poor visibility at night
  • Concrete roads have better visibility and less glare

It is essential that the road surface is visible at night and the reflection of light is the answer factor.


The pavement surface must be absolutely impermeable to prevent water seeping into the pavement layers. In addition, both the geometry and texture of the pavement surface should help remove water from the surface in a short amount of time.


Dr. Tom V Matthews (IIT Bombay)

Er. Mukesh Kumar

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Er. Mukesh Kumar is Editor in Chief and Co-Funder at ProCivilEngineer.com Civil Engineering Website. Mukesh Kumar is a Bachelor in Civil Engineering From MIT. He has work experience in Highway Construction, Bridge Construction, Railway Steel Girder work, Under box culvert construction, Retaining wall construction. He was a lecturer in a Engineering college for more than 6 years.