adminVEHICLES sometimes lose control at some point when negotiating curves. Navigating around a curve in a moving car is a skill that can take some time to master but with a little practice anyone can do it. Drivers need to understand the physical forces that influence the behaviour of vehicles on the road.
They need to also understand that there is a “lag time” for our air brakes (fitted on heavy vehicles and buses) to work while in a standard car that have hydraulic brakes, one only needs to depress the pedal and the brakes immediately start to slow down a car.
“Critical speed” of a curve
Every curve on a road has what is called the “critical speed”. I bet most drivers do not know this. If you drive faster than the “critical speed”, the vehicle will drive off the road. It does not matter how good you have been driving or how good you think you are.
If you exceed the “critical speed” of a curve, the vehicle will lose control. The “critical speed” of a curve is calculated using only two things, the radius (or sharpness) of a curve and the co-efficient of friction.
Co-efficient of friction of a roadway measures how slippery it is. If you plug the two into a formula, you will be able to calculate the critical speed of a curve.
As a curve gets sharper, or the road more slippery the “critical speed” goes down. For example, the same curve which you negotiated at 66km/h in dry weather should be negotiated safely at 44km/h if it is raining.
Driving faster than that speed will result in the vehicle veering off the road into whatever is on the side of the road. It will not be able to stay in the travel lane and safely negotiate the curve.
Centrifugal force
Centrifugal force is a natural law we have to contend with when driving. It is the force that pulls an object (vehicles in this case) out from the centre.
It comes into play when you are rounding a curve. It tends to pull your vehicle away from the inside edge, regardless of which direction you are travelling.
Let us see how it operates:
Explanation
Car 1 is going round a left hand curve, centrifugal force will carry it to the right across the centre line.
Car 2 is going round a right hand curve and centrifugal force will carry it to the left and off the road. If the driver of Car 2 tries to over compensate, he is likely to drive to his right and across the centre line.
As a result of the above explanation, if one driver allows centrifugal force to push him/her across the centre line and an oncoming driver compensates, a side swipe or a head-on collision could result.
The best way to take a curve
When you approach a curve you must slow down. Slow down before you enter a curve.
On right hand curves, keep to the centre of your side of the road.
On left hand curves, keep to the left hand side of your lane.
Gently apply power to the wheels to maintain a constant safe speed when the road is wet or slippery (the critical speed goes down), slow down more before entering the curve. You must also maintain a constant safe accelerator pressure.
Conclusion
If all drivers make an effort to understand how basic physics can take over the control of a vehicle and make them lose control when rounding curves, we will eliminate many such accidents.
Nature sets limits on how fast we can drive our vehicles. When a large vehicle equipped with air brakes tries to stop, it can’t stop as quickly as a car with hydraulic brakes.
If there is no visibility or minimal visibility around a curve, turn on your headlights to enable drivers coming from the other direction to see you.
Drive safely when negotiating curves. Together we can save millions of lives.
The writer, Ernest Muchena, is Traffic Safety Council of Zimbabwe’s Product Development and Marketing Manager who can be contacted on [email protected] or [email protected]
Online Reporter