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Of everything a vehicle does, stopping is the one function on which safety most directly depends. A vehicle that cannot accelerate well is merely slow. A vehicle that cannot stop well is dangerous. This post covers braking characteristics, the third of the three areas studied under traffic characteristics, and shows how braking behaviour feeds into three…

Roads are not designed around an average vehicle. They are designed around the demanding ones — the widest, the heaviest, the longest, the slowest to climb. Every dimension of a highway can be traced back to some property of a vehicle that had to be accommodated. This post works through the four vehicular characteristics that matter, and…

A road is a piece of engineering, but traffic is a crowd of human beings. Concrete behaves predictably. People do not. They get tired, they misjudge gaps, they panic, they take risks — and any road designed as though they were machines will fail. Traffic engineering therefore begins by studying the people and vehicles that…

A valley curve is the one place on a road where the design problem only appears after sunset. By day, a dip in the road hides nothing — you can see straight across it to the far side. At night, everything changes. Your headlights point slightly downward, and as the road curves upward away from…

Climbing a hill is hard work for a vehicle. Turning a sharp corner is also hard work. Ask a vehicle to do both at once and the engine may simply not have enough left to hold its speed. Grade compensation is the engineer’s answer: where a sharp curve lands on an already steep gradient, ease the…

Horizontal alignment deals with where a road goes. Vertical alignment deals with how it rises and falls along the way — and that has consequences you can feel from the passenger seat of any bus climbing a hill. This post covers the whole topic: what vertical alignment is, why steep grades cause so much trouble,…

Suppose a straight road ran directly into a circular curve, with no easing in between. At the exact point where they met, the driver would have to swing the steering wheel from centre to full lock instantly, and the vehicle would receive the full centrifugal force in a single jolt. Nobody drives like that, and…

Watch a long truck turn into a narrow gate and you will notice something odd. The front wheels swing wide around the corner, but the rear wheels cut inside them, sometimes climbing the kerb. The truck sweeps a wider band of ground than its own width. That everyday observation is the whole basis of this…

You now know that e + f = v2/(gR). But that single equation cannot, by itself, tell you how much to bank a curve — because it does not know that real roads carry both a speeding car and a crawling bullock cart on the same pavement. IRC therefore replaces the single formula with a sequence…

Watch a cyclist take a fast turn and you will see them lean inwards. They are not showing off — they are using gravity to help them turn. A banked road does exactly the same thing for a vehicle, except the road leans instead of the vehicle. This post explains that idea and then derives…