Daylight Hours

Daylight Hours


There is a peak in road traffic incidents (RTIs) when people are travelling to work and school in the mornings and a second peak in the evenings when they are travelling home. The peak in RTIs is much broader in the evenings because children and adults often do not go straight home, finishing work times are more flexible and they tend to socialise. Consequently, the evening peak lies fully or partially in darkness after the October clock change until the following spring. Vulnerable road users such as pedestrians and cyclists, especially those who do not wear brightly coloured clothing, are exposed to greater risk in the darker evenings.

In the UK clocks follow Greenwich Mean Time (GMT) in winter and British Summer Time (BST) in summer. The clocks go forward by one hour in March and back by one hour in October. There are both short-term and long-term effects of clock changes; the immediate effects related to the transfer of an hour of daylight, and the longer term effects of a long sequence of evenings in darkness.

Between 1968 and 1971 the government conducted an experiment where clocks were left on BST throughout the year. It was widely accepted that this resulted in a reduction in RTIs in the evenings, but there were more RTIs in the morning. Even though the reduction in the evenings outweighed the increased RTIs in the morning the experiment was concluded in 1971 and the UK reverted to the clock change regime that is still followed today.

In more recent times many organisations have advocated a change to the current clock change regime with the proposal of Single/Double Summer Time (SDST). In SDST clocks would be set to GMT+2 in summer and GMT+1 in winter, meaning one hour of daylight would be shifted from the morning to the evening throughout the year relative to the current regime.

The primary and most widely researched benefit of adopting SDST is that RTI rates would be reduced throughout the year, with an increase around sunrise but a larger reduction around sunset. Some researchers have used data from the 1970’s experiment to extrapolate and model how many road casualties would be saved, and the cost savings involved, if SDST was introduced.

According to various surveys, people in England are generally in favour of SDST, although there is some opposition in Scotland as the change would mean the sun would not rise until 10am in some areas. Some early morning workers may also have concerns

The campaign to introduce SDST has significant support in Parliament, but proposed bills have been ‘talked out’ by some MPs. Organisations such as RoSPA are calling for a new 2-3 year trial. The data from such a trial would be analysed using modern techniques and this would allow the arguments for and against SDST to be tested.


  • Date Added: 03 Apr 2012, 08:13 AM
  • Last Update: 27 Jan 2017, 03:56 PM