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Impact of 20mph Limits: Research Study and Findings

This research study examines the effectiveness of 20mph speed limits in different areas, analyzing journey speeds and safety data. The findings provide valuable insights for future policy development.

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Impact of 20mph Limits: Research Study and Findings

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  1. 20mph Research Study • Methodology, findings and next steps RSGB Analysts Conference, 5 March 2019Richard Fernandes (Atkins)

  2. Background • In 2013, DfT provided guidelines encouraging traffic authorities to consider introducing more 20mph limits over time • The DfT sought evidence to understand the impact of such implementations • Purpose of the research (published in Nov 18) • Examine the perceptions and attitudes of different user groups • Strengthen the evidence base regarding the effectiveness of 20mph limits • Inform future policy development on 20mph speeds and limits at a national and local level • Identify lessons learned regarding the implementation and monitoring of 20mph limits • Focuses on 20mph signed only limits

  3. Speed Analysis Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  4. Speed Analysis – The Challenge • Analyse the impact of 470km of new 20mph signed only across 11 locations • Challenges: • Measure the impact of the policy, and not background factors • Getting data that is representative of all roads • Granular data that allows monitoring of many metrics to be considered • No skewing based on seasonality of unusual events • Sufficient data to be confident of results Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  5. Speed Analysis - Data • Using two sources of data for greater insight: • TomTom GPS data comprising over 18 million vehicle kilometres to understand “journey speed” • - Provides information across breadth of study areas, by road segment • - Provides annual data, reducing reliance on any specific day • - Captures profile of speeds on each segment • Spot speed surveys at over 400 locations to understand “instantaneous speed” • - Gives detailed vehicle by vehicle speeds in granular format at set locations Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  6. Journey Speed Coverage in Brighton Phase 2 Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  7. Spot Speed Sites in Brighton Phase 2 Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  8. Speed Analysis - Methodology Journey Speed Only Statistical Comparison Weighted least squares model Speed Distribution Average Speed Median Mean Fastest Speeds 85th percentile Speed Range 15-85th percentile Threshold Speeds % <20, <24, <30mph Journey Speed Match on Geographic region Rural Urban Classification Index of Multiple Deprivation Instantaneous (spot) Speed Report on Overall impact Study area impact Road classification impact Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  9. Speed Analysis – Journey Speed Findings Actual change in speed: • Median speed fell by 0.7mph in residential areas and 0.9mph in city centre areas. Evidence of a 20mph limit impact: • Statistical analysis suggests that this is partly due to the implementation of 20mph limits, and partly reflects background trends in speeds on urban roads. • Statistically significant 20mph effect relative to comparators: • Residential: 0.4mph reduction in median speeds and 0.7mph reduction in 85th percentiles • City Centre: 0.6mph reduction in median speeds and 1mph reduction in 85th percentiles in city centre areas. Spot Speed results were similar though slightly larger reduction • Cumulative speed distribution in residential and city centre areas

  10. Road characteristics are important Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  11. Road characteristic effects speed more than speed limit Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  12. Safety Analysis Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  13. Safety Analysis - Data • Context: Existing research tells us that lower speeds may result in fewer collisions • Our approach: • Source: STATS19 Personal Injury Collision (PIC) data from the DfT: • Is used by this study to understand the change in collisions due to the introduction of 20mph • Records the location of PICs and supporting information on severity, casualties, vehicles etc • Not immediately available so requires patience: Any specific date of data can take between 9 and 21 months to be made available. • Before: use five years of PIC data in line with best practice • After: use as much PIC data as possible (ranging from 17-44 months) dependent on case study area

  14. Safety Analysis - Methodology Statistical Comparison Generalised Linear Model Match on Rural Urban Classification Region Date periods STATS19 Data Report on Overall impact Study area impact Road classification impact

  15. How have collision and casualty rates changed? (Residential areas) • Absolute number of collisions and casualties has decreased in both the case study and comparator areas. • Considerable fluctuation in the case study data, due to relatively small sample size, and random nature of collisions. (n = 1,575 collisions) • Much larger sample size for comparator areas, so smoother trend. • Statistical analysis indicates no significant difference in the trend in case study and comparator areas, in the short-term. Applies to: • collisions • casualties • pedestrians, cyclists • children, older persons • Collision trend in case study and comparator areas Case study areas Comparator areas

  16. How have collision and casualty rates changed? (City centre areas) Major routes within Brighton included within the 20mph implementation

  17. How have collision and casualty rates changed? (City centre areas) • Brighton Phase 1 is the only case study area where the change in collisions is found to be significant. • Based on relatively large sample size (n = 2,143). • Case study includes the city centre and surrounding areas. Scheme involved blanket implementation of 20mph limits, including higher flow A and B roads. • Significant reduction in collisions across all road types, but most pronounced on major strategic roads. • This represents just one case study and the findings are not necessarily transferable to other locations • Recommend analysis repeated once further post-scheme data has been collected • Collision trend in case study and comparator areas Brighton Phase 1 SE Comparator area

  18. Overall findings Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  19. Overall findings on 20mph • Speeds: • Has reduced speeds, though compliance often poor • Road characteristics important to the success and should be considered when implementing • Has a greater effect on the fastest of drivers • Safety: • No evidence of reduction, except in Brighton City Centre • Further research could provide more weight to this finding • Perceptions and attitudes: • Strong support for 20mph amongst cyclists and residents • Only 12% of residents and 21% of non-resident drivers would want speed changed back • Main area of concern is around compliance

  20. What next for 20mph signed only? • Potential to reapply methodology to other local authority schemes to understand localised impacts, especially around speeds • Potential to explore further the contextual factors that lie behind compliance. Explore ways to give motorists the cues for lower speed driving • Healthy Streets approach in London, looking at making London greener, healthier and more attractive through integrated delivery of measures with 20mph as part of the overall approach Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  21. Questions Change Footer here: Insert > Header and Footer (delete if none) Contains sensitive information

  22. Spare/Backup Slides • Boilerplates

  23. How have collision and casualty rates changed? • Police data on road collisions (STATS19 data) used to examine collisions before and after implementation of 20mph limits. • Comparator areas identified for each case study area to control for background trends in collisions relating to factors such as technology improvements, economic trends, road type, environment. • All comparator areas comprise urban 30mph roads with similar geographical characteristics (in terms of urban form and density) to case study areas. • Purpose of the comparator areas is estimate what would have happened in the case study locations if the 20mph limits had not been implemented. • 5 years before data. Between 17 and 44 months of after data. • Statistical model used to test for relative change in case study vs comparator areas.

  24. Location of new 20mph limits (by road type) and collision density in Brighton Phase 1 (pre-scheme)

  25. The Research (2014-2018) • Purpose of the research (published in Nov 18) • Examine the perceptions and attitudes of different user groups • Strengthen the evidence base regarding the effectiveness of 20mph limits • Inform future policy development on 20mph speeds and limits at a national and local level • Identify lessons learned regarding the implementation and monitoring of 20mph limits • Focuses on 20mph signed only limits

  26. Methodology Approach • Only major UK study to date to consider multiple case study areas and provide a national picture. • Combines evidence from 12 case study schemes comprising over 700kms of 20mph limits • 2 small-scale residential, 8 large-scale residential, 2 city centre-focused schemes • Uses data from comparable locations where 20mph limits have not been introduced to control for background trends • Focuses on strengthening the evidence base on perceptions, speed, early safety outcomes, and also considers walking and cycling benefits. • No primary data collected on air quality, greenhouse gas emissions, noise levels, or health as part of this study. Quantitative and qualitative data sources • Over 5,400 questionnaires with residents, drivers, cyclists and motorcyclists • Interviews with 177 drivers, and 9 focus groups • Over 60 interviews with local stakeholders. • Analysed over 18 million veh-kms of journey speed data, and spot speed data for over 400 locations • Almost 4,000 collisions analysed in 20mph limit areas.

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