THE city council bases part of its case for reducing speeds in York on a Transport Research Laboratory (TRL) report first produced in 2000: “The effects of drivers’ speed on the frequency of road accidents”.

The authors of the report measured the speed at which more than two million observed drivers actually drove on more than 300 sections of road (78 of them in England, the remainder in other countries) and correlated this information with the number of road accidents that occurred on these roads.

More than 10,000 drivers also completed questionnaires.

The report concluded that there was a clear link between speed and the number of accidents. It estimated that for every 1mph actual reduction in the average speed of motorists using a road, the likelihood of an accident would reduce by

- about 6 per cent for urban roads with low average speeds

- about 4 per cent for urban roads with medium average speeds and for rural roads with lower speeds

- about 3 per cent for urban roads with higher speeds and rural main roads.

These are the figures that City of York Council quotes when asked for evidence. In urban areas, however, the TRL report noted that the potential to reduce accidents by reducing speeds was greatest on “busy main roads in towns with high levels of pedestrian activity, wide variation in speeds, and high accident frequency’.

It could be argued that these are the very roads in York where the new 20mph limits will NOT be introduced.

Another point the TRL report makes is that the best way to reduce accidents on urban roads is to bring down the speeds of the fastest drivers, rather than reducing the overall average speeds. In other words, crack down on the boy racers who persistently break urban speed limits, rather than reduce those speed limits.

The TRL report does not look specifically at the issue of 20mph limits.

The city council does, however, cite some research carried out on 20mph zones.

This was conducted by the London School of Hygiene and Tropical Medicine (LSHTM) and was published in the British Medical Journal in 2009.

A team from the LSHTM carried out an “observational study based on analysis of geographically-coded police road casualty data’ in London between 1986 and 2006. The study concluded that “The introduction of 20 mph zones was associated with a 41.9 per cent reduction in road casualties... The percentage reduction was greatest in younger children and greater for the category of killed or seriously injured casualties than for minor injuries.

There was no evidence of casualty migration to areas adjacent to 20 mph zones, where casualties also fell slightly by an average of 8.0 per cent.”