One can understand from the passage that the majority of motorway accidents are catastrophic ____ .

Certain features of the motorway undoubtedly ease the
strain of driving. Gradients and bends are so controlled as
to obviate the necessity of sharp braking and the absence
of traffic approaching from the other direction removes
one of the commonest sources of accidents. Many
dangers remain, however, made more terrible by the high
speeds of vehicles. A collision at seventy miles an hour is
almost inevitably in its results. A mechanical defect in the
car or a puncture can lead to loss of control and
catastrophe. The car should be completely roadworthy
and tyre pressures and treads need to be checked at
regular intervals.