Bristol evaluation shows 20mph saves lives

The report commissioned by Bristol City Council into the effects of 20mph is now available. The key findings are:

Speed
• On average, according to Automatic Traffic Count (ATC) speed data (with over 36 million vehicle observations analysed) there was a statistically significant 2.7mph decrease in vehicle speeds on roads where the 20mph speed limit was introduced, when controlling for other factors that might affect speed (areas, calendar year, time of day, season, type of road, and day of week). In the areas that stayed 30mph, there was a statistically significant negligible reduction in speed (0.04 mph)
• The largest reduction in speed was on 20mph A and B roads.
• Average speeds on 20mph roads were found to be below 24 mph in every area except for the Outer North and South areas of Bristol. On 30mph roads, average speeds are below 30mph in every area.
• Average speeds declined by a greater amount in the summer months and on weekends, where traffic volume (and congestion) is lowest.
• 94% of roads surveyed saw a reduction in average speeds. Average speed decreased on 100 roads out of 106.

Casualties
• Annual rates of fatal, serious, and slight injuries following the introduction of the 20mph speed limits are lower than the respective pre-20mph limit rate, thus showing a reduction in the number of injuries. The estimated total number of injuries avoided across the city each year is 4.53 fatal, 11.3 serious, and 159.3 slight injuries.
• The estimated annual saving following the decrease in casualties is £15,256,309 based on Department for Transport formula for calculating the cost of road traffic casualties.
• The decrease in casualties has also benefitted some vulnerable groups. It is estimated that:

  1. Two child lives will be saved every three years; 3 older adult lives will be saved every two years; and 3 pedestrian deaths will be avoided every year.
  2. More than 4 child serious injuries will be avoided in just over three years; 4 older adult lives will be saved in three years; and 2 pedestrian severe injuries will be avoided every year.
  3. The number of avoided slight child injuries per year is 7.68; 25.77 older adult slight injuries will be avoided each year; and 24.54 pedestrian slight injuries will be avoided each year.

Wider public health effects
• Clear majority support remains in Bristol for 20mph speed limits, with 62% supporting such limits on residential roads and 72% on busy streets.
• However, there is cynicism in Bristol about lack of enforcement of 20mph limits, a lack of compliance from “other drivers” and an increased readiness to report that it is sometimes okay to drive above the posted speed limit on residential roads.
• The number of people who walk or cycle to work in Bristol has increased between 2010 and 2015.
• More children in Bristol now walk or cycle to school following the introduction of the 20mph speed limits.

Conclusions
• This study has found statistically significant reductions in average traffic speeds of 2.7mph across the city of Bristol, following the introduction of 20mph speed limits. This is a larger reduction than seen in previous evaluations in other cities.
• The study employed a more sophisticated analysis than previous studies of 20mph limits, including using individual speed data from over 36 million vehicle observations and controlling for other factors that might affect changes in traffic speeds.
• There has been a reduction in the number of fatal, serious and slight injuries from road traffic collisions, equating to estimated cost savings of over £15 million per year.
• Although there is still majority support for 20mph speed limits in Bristol, there remains concern about compliance and behaviour of other drivers.
• Walking and cycling across Bristol has increased, both among children travelling to school and adults travelling to work.
• The introduction of 20mph speed limits in Bristol offers a model for other towns and cities across the UK, who are seeking to reduce traffic speeds, cut road traffic casualties, and promote community health and well-being through road danger reduction.
• In order to assess effectiveness of 20mph speed limits, it is vital that other towns and cities follow Bristol’s example, and prioritise the ongoing collection and analysis of appropriate data on vehicle speeds, road traffic casualties and wider public health impacts.

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