Effect of centrifugal force on horizontal curve

When a vehicle moves along a horizontal curve of radius $R$ at speed $v$, a centrifugal force $P = \dfrac{Wv^2}{gR}$ acts outwards (horizontally, through the centre of gravity). The ratio $P/W = v^2/(gR)$ is called the centrifugal ratio. It has the following effects:

1. Tendency to overturn the vehicle about the outer wheels, because $P$ acts at the height $h$ of the centre of gravity, while the weight $W$ resists with a lever arm of $b/2$ ($b$ = wheel track). Overturning begins when $$\frac{v^2}{gR} \ge \frac{b}{2h}$$
2. Tendency to skid sideways (lateral skidding) outwards when $P$ is more than the lateral friction $fW$: $$\frac{v^2}{gR} \ge f$$
3. Discomfort and strain to passengers and the load; the load may shift in goods vehicles.
4. Reduced steering control: the driver drifts to the outer edge and may encroach on the opposite lane.
5. Uneven tyre wear and higher fuel use due to lateral slip.
6. Higher chance of accidents, especially for vehicles with a high centre of gravity (trucks, buses) or on wet roads.

Remedies: superelevation, an adequate radius, a transition curve, speed restriction, and warning signs. Normally $f < b/2h$, so a vehicle skids before it overturns.