One of the reasons for driving in rain being more hazardous is reduced traction on

wet roads. All driving maneuvers but especially stopping need to be adjusted for the slippery conditions. This invites a review of the laws of “driving” physics.

To perceive that braking is required is estimated to take about three-quarters of a second. This means that the average driver traveling at 90 kmh will have traveled 20 metres before he or she has fully comprehended the need to slow down. It then takes, on average, another three-quarters of a second to initiate braking by moving from the gas pedal to the brake pedal…and thus another 20 metres is covered. In total then, a distance of 40 metres is covered even before the vehicle begins to brake.

*mass*they carry, the

*harder*they resist.

The higher the speed, the more time and distance it takes to stop. For example, at 110 kmh, perception and reaction distance equals 47 metres, and braking distance equals 57 metres, a total of 104 metres (5.2 seconds). At 130 kmh it takes over 128 metres (5.7 seconds) to stop a vehicle, and at 140 kmh more than 155 metres (6.2 seconds), over a tenth of a kilometer.

These computations are based on dry pavement, using an average braking rate of .870 g. On wet roads, the braking rate drops considerably—from .870 g to .600 g.—and the braking distance grows exponentially. At 90 kmh, braking time increases from 4.6 seconds to 6.1 seconds, and braking distance increases from 82 metres to 101 metres.

## Comments

The writer of this column says that 90 kph is equal to 60 miles per hour. That is incorrect.

100 kph = 62.5 Miles per hour, and 90 kph is equal to 55.92 kph.