Speed Indicator Devices in London: Do they Work? Peter Sadler London Road Safety Unit

1. Speed Indicator Devices in London: Do they Work? Peter Sadler London Road Safety Unit

2. Background Questions from Boroughs • Do SIDs work? • When do they work best? • Does everyone slow down for SIDs? • How are SIDs best used?

3. Background • Aim to inform and educate drivers about speed so that they change their speed • Can be set to display a happy / sad face leading to feelings of comparison or embarrassment • Can be set to not display a speed over a set threshold to stop irresponsible drivers

4. Background • Speed Indicator Devices (SIDs) are increasingly being used in London and the UK • The display and operation of a SID is different to that of Vehicle Activated Signs (VAS) (TAL 1/03) • Little evidence currently exists on the effectiveness of SIDs in reducing vehicle speeds Therefore, LRSU commissioned TRL to undertake a study into the effectiveness of SIDs in reducing vehicle speeds in London

5. Background: Electronic activated signs Fig 1. VAS Fig 2. SID

6. Background : SIDs versus VAS

7. Study aims • Investigate speeds before, during and after SID installation • Produce case study on SID good practice • Assess the contribution SIDs can make in improving road safety in London

8. Site selection (10 study sites) Sites were selected from South East borough roads if they passed all inclusion and exclusion criteria • Single carriageway 30mph road • No other traffic calming features present • Sufficient road length for measurements (1.2km) • Curvature of road allowed SID operation • History of speed related collisions (all severities), or • Documented speeding problem by the borough

9. Data collection 1 Using ATC tubes speed and flow data were collected for a week before,during and after the SID operation 200 metres before SID At SID location 200 metres beyond SID 400 metres beyond SID

10. Data collection 2 ATC failure, vandalism and SID failure meant some periods did not have data recorded. Overall, enough data was recorded to allow a robust analysis of the study questions • Before tube allows for control of background speed changes • At SID tube measures change due to SID • 200 metres and 400 metres beyond SID measure downstream effect

11. Descriptive results

12. Descriptive Results: King Henry’s Drive – Mean speed Before mean speeds

13. Descriptive Results: King Henry’s Drive – Mean speed Before mean speeds During mean speeds

14. Descriptive Results: King Henry’s Drive – Mean speed After mean speeds Before mean speeds During mean speeds

15. Analysis • All sites had ‘free flowing’ traffic conditions defined (vehicles travelling less than 20mph or with less than 2 seconds headway were excluded) • Missing data periods omitted from analysis • Days with missing data had weighted data calculated • ANOVA (Analysis of Variance) analysis undertaken for all research questions

16. Results 1: Effect on speeds Table 1: Difference in mean vehicle speeds during SID operation to before mean vehicle speeds (All sites) * Statistically significant at the 5% level from the before period At sites where a SID failed mean vehicle speeds were reduced by 0.5mph

17. Results 2: Effect on speeding drivers Table 2: Proportion of vehicles exceeding speed limit (All sites) * Statistically significant at the 5% level from the before period

18. Results 3: Effect on speeds over time Table 3: Difference in mean vehicle speeds during and after SID operation to before mean vehicle speeds Note: Not enough data for change to be calculated in during week 3 * Statistically significant at the 5% level from the before speed

19. Results 4: Effect on vehicle speeds by site characteristics Table 4: Road characteristics and reduction in mean vehicle speeds at SID sites Note: Some road characteristics were only present at one site

20. Results 5: Potential effect of SIDs on collisions • Collisions reduce by 5% for every 1mph reduction in mean speed • Based on an overall reduction in mean speeds of 1.4mph it has been calculated that SIDs could reduce collisions by 5.6% • This effect would only be present while the SID was operational for 2 to 3 weeks and for around 200 metres beyond the SID sign

21. Case study for good practice: Royal Borough of Kingston-upon-Thames Data led rotation programme • Based on several years of experience, data collection and research Kingston have developed a rotation programme for their SIDs to maximise efficiency • SIDs are located where speeding problems are known to be present through speed data collection • Speed management policy document sets out site selection criteria for SIDs and where other speed management tools should be used

22. Case study for good practice: Royal Borough of Kingston-upon-Thames Features of the rotation programme • 13 SIDs rotated around 90 sites every three weeks • Rotation takes two people one day every three weeks • SIDs powered by mains feed from lamp column to avoid battery life issues • Backing plate and power lead results in fast and easy installation • SIDs popular with local residents and school children

23. Conclusions • SIDs are effective at reducing vehicle speeds while they are operational and effective • Vehicle speeds begin to increase as the SID deployment continues • There is no residual effect after the removal of a SID • SIDs can contribute in a small way to a speed management strategy in conjunction with other engineering measures

24. Contact • Report available on • www.tfl.gov.uk/roadsafetyreports • Peter.Sadler@tfl.gov.uk • 020 3054 1081 • Road Safety Researcher - London Road Safety Unit • Transport for London 9th floor zone Y3, Palestra, • 197 Blackfriars Road, London SE1 8NJ