Motorists have been urged to slow down near schools after research described as “extremely concerning”.
Analysis of vehicle speeds outside a primary school in Berkshire found that more than a fifth (21%) of drivers exceeded the 30mph speed limit.
Cars found speeding drove at an average of 34.1mph.
Churchill Motor Insurance, which commissioned the experiment, warned that driving at that speed creates a stopping distance in dry conditions of 58.3 metres, compared with 46.7 metres at 30mph.
A spokesman for the insurance firm said: “The findings are extremely concerning given drivers are using roads where lots of young children will be crossing and it is often hard to see around parked cars.”
It added: “Driving over the speed limit, even by the slightest amount, can have a serious impact on braking distances.
“Young children don’t always have the best road safety awareness and may run out from between parked cars, so if a car was travelling above the speed limit when this happened, it may not be able to stop in time, leading to a tragic accident.”
The analysis was carried out on Bray Road near Oldfield Primary School, Maidenhead over a two-week period during term time in January.