Road safety: time for change?

21st Jun 2010

Britons waking up to the longest day of the year this morning were asked by the 10:10 climate campaign to consider permanently shifting the clocks forward by one hour. A report by Dr Elizabeth Garnsey, from the University of Cambridge, is being launched by the group at a Parliamentary event to tie-in with the summer solstice, and 10:10 claims that the adoption of Single Double Summer Time (SDST) could produce a wealth of benefits for the UK.

The Claim

Besides the positive economic and environmental impact that 10:10 attributes to its 'Lighter Later' initiative stands a rather eye-catching claim: that by operating on Central European Time (GMT +1 during the winter, and GMT +2 during summer) the UK could actually save 100 lives every year. According to campaigners, this is achieved through increasing daylight - and hence visibility — for the times when most accidents occur: the afternoon rush-hour.

But this claim has not gone unchallenged. As a Greater London Assembly report on the proposed changes to daylight hours noted 'the effect on road accidents in the hours of darkness is the issue which has given rise to the most heated debate in relation to clock time. It has been argued that reduced daylight in the morning when children are going to school would be likely to lead to an increase in road accidents.'

This is particularly true in Scotland, where the trial introduction of year-round British Summer Time (BST) between 1968-71 was blamed for a number of high-profile morning road accidents involving school children. With some Scottish residents interviewed on the issue for the BBC's Daily Politics Show still sceptical about any road safety benefits, Full Fact decided to investigate the factual basis for the Lighter Later claims.

Analysis

Lighter Later's claim that SDST reduces road traffic deaths is founded on research published by the Transport Research Laboratory that reported that the proposed change in daylight hours would result in around 450 fewer casualties of road accidents, including between 104 and 138 fewer deaths, depending upon the assumptions made. Given that Lighter Later has used a figure at the lower end of this scale, its claim may be seen as a conservative estimate.

However these assumptions themselves have been the source of some controversy. Subsequent research from Arthur Huang and David Levinson has suggested that the impact of weather on road traffic data had not been adequately modelled by the Transport Research Laboratory report. Whilst agreeing that daylight saving measures do reduce crashes, Huang and Levinson reported moving the clocks forward is also associated with higher odds of fatal crashes and greater traffic congestion.

The Royal Society for the Prevention of Accidents (RoSPA) — which is backing the Lighter Later campaign - also cites a trial conducted between 1968 and 1971 during which BST was adopted all year round in certain regions of England and Scotland as further evidence of the efficacy of SDST in increasing road safety. It claims that around 2,500 deaths and serious injuries were prevented each year of the trial period because of the measures.

As RoSPA itself recognises, this claim doesn't necessarily tally with the 'folk memory' of the trial, where high-profile deaths amongst school children in road traffic accidents was linked by the media to the darker mornings precipitated by the change. The popular perception of the trial as a failure persist, as evidenced  in a recent Mumsnet discussion on the proposed changes, however analysis of Department for Transport figures conducted by Tim Yeo as part of a research paper on the issue shows that fatalities were indeed down eight per cent, with all casualties also two per cent lower during the trial period.

The extent to which this success can be attributed to the changes in daylight hours is more uncertain however, with some reports suggesting that changes to the drink-driving law made in 1969.

Whilst no allowances were made for this in an initial report on the 1968-71 trial by The Department of Transport's Transport and Road Research Laboratory, a DfT spokesperson did explain to Full Fact that this should not necessarily detract from the report's validity.

She said: "Because the daylight saving measures impact only upon the periods of morning and afternoon during which sunrise and sunset occur, the number of road traffic accidents recorded during these times should not have been affected by the 1969 drinking legislation, which largely targeted after-dark drinking.

"The Transport and Road Research Laboratory report looked at the data for these periods closely, and we're confident that its findings were accurate."

Conclusion

Whilst questions have been raised about their methodology, there does seem to be a growing consensus amongst researchers that the use of daylight saving measures can have a positive impact upon road safety.

Lingering doubts about the impact of external factors such as weather and related drink-driving legislation on trial findings may remain, as will questions about the age of the data pertaining to the 1968-71 pilot.

However the best available indicators do seem to concur with the claims made for the Lighter Later campaign.

Nevertheless, the fact that the loudest objections to the proposals come from Scotland is telling. As RoSPA noted in its report, Scotland was the one area of the UK that reported an increase in traffic incidents during the 1968-71 trial, due to the fact that its northerly location delays sunrise under the proposals until well into the morning.

Recognising this, RoSPA notes that the Scottish Parliament may have a role in legislating for separate time zones, and it is worth accounting for such regional nuances when considering Lighter Later's claim.