In message , Clive D. W. Feather
writes

The actual number of car journeys that consist only of the "school run"
are not that large compared with the other work-related journeys.
However, the belief is that the combination of this small extra number,
combines with the fact that people who both drop off their child and
going to work will be more spread out in the holidays (having more
choice of arrival time) - the result is to push the road over the
threshold between "within capacity" and "overloaded".

It is not just pupils who arrive at school by car. Most of the country's
half a million school teachers go to and from school by car; then
there's all the ancillary workers - then add to that the fact that staff
in Higher Education are also likely to be on holiday and that students
with cars will not be driving in and out of college in the vac.

All in all, that's probably close on a million people not driving to and
from school/college at the normal times, even without the "school run"
journeys.

--
Paul Terry