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NIHR Signal Building an urban motorway did not reduce traffic accidents locally

Published on 20 July 2016

doi: 10.3310/signal-000269

Extending the M74 motorway above Glasgow’s existing road network in 2011 has not affected the number or severity of road traffic accidents in the area. While the number of accidents fell by around 50% between 1997 and 2014, similar reductions were seen across other areas not affected by the motorway, suggesting a general trend of improved road safety.

Accidents are common on the UK’s roads. Interventions to reduce the number of accidents usually focus on education (e.g. drink-driving awareness campaigns), legal measures (e.g. speed limits) or infrastructure (e.g. traffic calming measures like speed bumps). This study investigated the impact of an infrastructure change.

Reducing the number of traffic accidents was one of the main benefits predicted for the new road, which did not happen in this case. This suggests that it should not be taken for granted that future motorway construction will reduce accidents.

Share your views on the research.

Why was this study needed?

In the UK five people a day are killed in road traffic accidents, with a further 60 seriously injured. Nearly 75% of accidents in the UK occur where the speed limit is 40 miles per hour or less. Motorway travel is safer and only 5.4% of fatalities from accidents occur there despite them carrying 21% of traffic.

In Glasgow a 5 mile extension of the M74 motorway was constructed above existing roads to connect the M74 to the M8. Its aim was to improve travel between the East and West of Scotland and reduce traffic on Glasgow’s non-motorway roads. Its construction was controversial, but one of the major benefits predicted was that by taking traffic away from smaller roads it might reduce the number of accidents locally.

This study aimed to evaluate the impact of this new motorway on the number, severity and types of road users involved in accidents.

What did this study do?

This study used data from a UK national database of road traffic accidents that have been reported to the police and resulted in a casualty. It focused on three areas in Glasgow – the area immediately around the motorway extension, the area surrounding another existing motorway, and an area without a motorway. Data for the whole of Glasgow was also used to establish broader accident trends.

The study looked at the number and severity of accidents at specific points – an approach called an “interrupted time series analysis” – between 1997 and 2014: prior to construction in 2008, during construction 2008-2011 and after opening in 2011. Data on the amount of traffic on the different roads included in the study was not reliable, so the analysis could not be adjusted to account for how busy the roads were.

What did it find?

  • The overall number of road traffic accidents between 1997 and 2014 fell by 50.7% in the area around the motorway extension (from 758 to 374), 49.3% in the area around the existing motorway (from 292 to 148) and 50.5% in the area without a motorway (from 315 to 156).
  • There was no effect on the number of accidents during the construction or after the opening of the motorway extension.
  • There were significant reductions in the number of serious and fatal accidents across all road user types. The area around the motorway extension had a lower reduction in pedestrian casualties of 52%, compared with 65 to 69% in the other areas studied.

What does current guidance say on this issue?

NICE produced guidelines in 2010 on preventing road traffic accidents involving children under 15 years of age and guidelines for preventing unintentional injuries in under 15 year-olds. Both made varied recommendations include the introduction of 20 miles per hour limits and zones and the use of design measures to reduce speed or improve safety. No specific recommendations relate to motorways. NICE recommended that programmes should be evaluated using a range of outcome measures, including road injury data.

Transport Scotland has a Road Safety Framework strategic plan in place to reduce the number of people killed on its roads by 40% by 2020. Its plan includes various policies for reducing speed, focusing increasing safety for motorcyclists, pedestrians and cyclists, and targeting interventions at young drivers (aged 17 to 25) and older drivers. It addresses road design to reduce casualties, such as pavements and cycle lanes.

The Highway Code provides guidance for all road users on how to safely and legally use the roads.

What are the implications?

During the study period traffic accidents were reduced across all three areas in Glasgow, with no significant differences between the different areas covered. This suggests that the introduction of a new urban motorway did not have the expected effect of reducing accidents. The fall in the number of accidents across the city is impressive and parallels UK-wide trends. City-wide programmes and other educational and legal interventions seem likely to have impacted on the number of road accidents. This study is part of a wider evaluation programme examining the impact of the M74 motorway extension on local communities, such as impacts on mental health and use of public transport.

The study focused on accidents only. There are other public health considerations in road construction, such as air pollution and the impact on “active transport”, such as walking or cycling. These are worthy of investigation in their own right.

Citation and Funding

Olsen JR, Mitchell R, Mackay DF, Humphreys DK, Ogilvie D; M74 study team. Effects of new urban motorway infrastructure on road traffic accidents in the local area: a retrospective longitudinal study in Scotland. J Epidemiol Community Health. 2016. [Epub ahead of print].

This project was funded by the National Institute for Health Research Public Health Research programme (project number 11/3005/07).

Bibliography

Brake. Road safety facts. Huddersfield: Brake; updated 2016.

Department for Transport. The highway code. London: Department for Transport; 2016.

Lyons RA, Ward H, Brunt H, et al. Using multiple datasets to understand trends in serious road traffic casualties. Accid Anal Prev. 2008;40(4):1406–10.

NICE. Unintentional injuries: prevention strategies for under 15s. PH29. London: National Institute for Health and Care Excellence; 2010.

NICE. Unintentional injuries on the road: interventions for under 15s. PH31. London: National Institute for Health and Care Excellence; 2010.

Transport Scotland. Road safety framework: mid-term review. Glasgow: Transport Scotland; 2016.

Transport Scotland. The road safety framework, targets and reducing road casualties. Glasgow: Transport Scotland; 2016.

Why was this study needed?

In the UK five people a day are killed in road traffic accidents, with a further 60 seriously injured. Nearly 75% of accidents in the UK occur where the speed limit is 40 miles per hour or less. Motorway travel is safer and only 5.4% of fatalities from accidents occur there despite them carrying 21% of traffic.

In Glasgow a 5 mile extension of the M74 motorway was constructed above existing roads to connect the M74 to the M8. Its aim was to improve travel between the East and West of Scotland and reduce traffic on Glasgow’s non-motorway roads. Its construction was controversial, but one of the major benefits predicted was that by taking traffic away from smaller roads it might reduce the number of accidents locally.

This study aimed to evaluate the impact of this new motorway on the number, severity and types of road users involved in accidents.

What did this study do?

This study used data from a UK national database of road traffic accidents that have been reported to the police and resulted in a casualty. It focused on three areas in Glasgow – the area immediately around the motorway extension, the area surrounding another existing motorway, and an area without a motorway. Data for the whole of Glasgow was also used to establish broader accident trends.

The study looked at the number and severity of accidents at specific points – an approach called an “interrupted time series analysis” – between 1997 and 2014: prior to construction in 2008, during construction 2008-2011 and after opening in 2011. Data on the amount of traffic on the different roads included in the study was not reliable, so the analysis could not be adjusted to account for how busy the roads were.

What did it find?

  • The overall number of road traffic accidents between 1997 and 2014 fell by 50.7% in the area around the motorway extension (from 758 to 374), 49.3% in the area around the existing motorway (from 292 to 148) and 50.5% in the area without a motorway (from 315 to 156).
  • There was no effect on the number of accidents during the construction or after the opening of the motorway extension.
  • There were significant reductions in the number of serious and fatal accidents across all road user types. The area around the motorway extension had a lower reduction in pedestrian casualties of 52%, compared with 65 to 69% in the other areas studied.

What does current guidance say on this issue?

NICE produced guidelines in 2010 on preventing road traffic accidents involving children under 15 years of age and guidelines for preventing unintentional injuries in under 15 year-olds. Both made varied recommendations include the introduction of 20 miles per hour limits and zones and the use of design measures to reduce speed or improve safety. No specific recommendations relate to motorways. NICE recommended that programmes should be evaluated using a range of outcome measures, including road injury data.

Transport Scotland has a Road Safety Framework strategic plan in place to reduce the number of people killed on its roads by 40% by 2020. Its plan includes various policies for reducing speed, focusing increasing safety for motorcyclists, pedestrians and cyclists, and targeting interventions at young drivers (aged 17 to 25) and older drivers. It addresses road design to reduce casualties, such as pavements and cycle lanes.

The Highway Code provides guidance for all road users on how to safely and legally use the roads.

What are the implications?

During the study period traffic accidents were reduced across all three areas in Glasgow, with no significant differences between the different areas covered. This suggests that the introduction of a new urban motorway did not have the expected effect of reducing accidents. The fall in the number of accidents across the city is impressive and parallels UK-wide trends. City-wide programmes and other educational and legal interventions seem likely to have impacted on the number of road accidents. This study is part of a wider evaluation programme examining the impact of the M74 motorway extension on local communities, such as impacts on mental health and use of public transport.

The study focused on accidents only. There are other public health considerations in road construction, such as air pollution and the impact on “active transport”, such as walking or cycling. These are worthy of investigation in their own right.

Citation and Funding

Olsen JR, Mitchell R, Mackay DF, Humphreys DK, Ogilvie D; M74 study team. Effects of new urban motorway infrastructure on road traffic accidents in the local area: a retrospective longitudinal study in Scotland. J Epidemiol Community Health. 2016. [Epub ahead of print].

This project was funded by the National Institute for Health Research Public Health Research programme (project number 11/3005/07).

Bibliography

Brake. Road safety facts. Huddersfield: Brake; updated 2016.

Department for Transport. The highway code. London: Department for Transport; 2016.

Lyons RA, Ward H, Brunt H, et al. Using multiple datasets to understand trends in serious road traffic casualties. Accid Anal Prev. 2008;40(4):1406–10.

NICE. Unintentional injuries: prevention strategies for under 15s. PH29. London: National Institute for Health and Care Excellence; 2010.

NICE. Unintentional injuries on the road: interventions for under 15s. PH31. London: National Institute for Health and Care Excellence; 2010.

Transport Scotland. Road safety framework: mid-term review. Glasgow: Transport Scotland; 2016.

Transport Scotland. The road safety framework, targets and reducing road casualties. Glasgow: Transport Scotland; 2016.

The effects of new urban motorway infrastructure on road traffic accidents in the local area: a retrospective longitudinal study in Scotland

Published on 8 June 2016

Olsen, J et al.

Journal of Epidemiology & Community Health , 2016

Background The M74 motorway extension, Glasgow, opened in June 2011. One justification for construction was an expectation that it would reduce road traffic accidents (RTAs) on local non-motorway roads. This study evaluated the impact of the extension on the number of RTAs, stratifying by accident severity. Methods Data for the period 1997–2014 were extracted from a UK database of reported RTAs involving a personal injury. RTA severity was defined by the level of injury: minor, severe or fatal. RTAs were assigned to (1) the local area surrounding the motorway extension, (2) a comparator area surrounding an existing motorway or (3) a control area elsewhere in the conurbation. Interrupted time-series regression with autoregressive integrated moving average (ARIMA) errors was used to determine longitudinal between-area differences in change in the number of RTAs, which might indicate an intervention effect. Results Glasgow and surrounding local authorities saw a 50.6% reduction in annual RTAs (n: 5901 to 2914) between 1997 and 2014. In the intervention area, the number of recorded RTAs decreased by 50.7% (n: 758 to 374), and that of fatal/severe RTAs by 57.4% (n: 129 to 55), with similar reductions in the comparator/control areas. The interrupted time-series analysis showed no significant between-area differences in temporal trends. The reduction of pedestrian casualties was attenuated in the intervention area relative to Glasgow and surrounding authorities. Conclusions Reduction in RTAs was not associated with the motorway extension. Our findings suggest that in planning future investment, it should not be taken for granted that new road infrastructure alone will reduce RTAs in local areas. Urbanisation is proceeding rapidly worldwide, and evidence of infrastructure changes is lacking; this novel study provides important findings for future developments.

Expert commentary

This study showed that a motorway extension in a developed country with a good road safety record did not reduce casualties in the surrounding urban area over and above downward trend. The implications of this study are that transport planners and engineers need to reconsider justifying investment in new road infrastructure on the basis that they will reduce collisions in the surrounding areas. Reducing injuries in urban areas clearly requires a more holistic approach. Rigorous scientific evaluations like these are needed to understand the contribution of infrastructure investment to preventing road casualties in urban areas.

Dr Nicola Christie, Director, UCL Transport Institute