Speed Humps
Speed humps have a short rounded top which is typically 75mm high.
The ramps either side are painted with white arrows to make them more obvious to motor vehicle drivers.
The aim of the speed hump is to slow motor vehicle traffic to a safe speed, as the ramps become uncomfortable for vehicle drivers if they are driven over too fast.
Disadvantages
- Buses, cyclists and emergency vehicles may need to slow down
- Bus companies normally oppose speed humps
- Some motor vehicle traffic is likely to transfer onto alternative routes, potentially causing a problem somewhere else
- Large vehicles travelling over speed humps cause vibration in nearby homes (e.g. lorries)
- Signs are required to warn drivers of speed humps, and these contribute to sign clutter
- These signs must be illuminated, which may caused further concerns in conservation areas
Considerations
- May cause traffic to divert to other routes
- Speed humps could create noise and vibration which is heard and felt in residences nearby. A greater distance between speed humps and residences will reduce this problem.
- Require a 'Road Hump regulation order' before installation
Advantages
- More effective than speed cushions and horizontal treatments at reducing vehicle speeds
Effectiveness
Generally, vertical treatments - such as speed humps - are expected to reduce accidents by around 44%.
Motor vehicles are likely to travel at around 15 mph over a speed hump. If there's a series of speed humps, vehicles are likely to travel at 20 mph between them.
Speed humps do not slow motor vehicle traffic as much as speed tables, however they are more effective than speed cushions.
Reducing motor vehicle speeds increases safety because:
- The vehicle has travelled less distance before the driver can react to a hazard
- Braking distance is reduced, so the vehicle can stop more quickly before a hazard
- A slower moving vehicle will exert less energy on occupants as the vehicle rapidly changes speed on impact (crashes)
- A slower moving vehicle will transfer less energy to a pedestrian in the event of a collision
Restrictions
- Speed humps are used on residential roads or busy pedestrian areas
- Shouldn't be used on bus routes
There's also some general restrictions to note for all schemes
Advanced information
Likely motor vehicle speeds when travelling over a speed hump are taken from TRL report 186 (Webster & Layfield, 1996). The research was based on Local Authority data at thirty-three 75mm high round-top humps from around England. All sites had a 30 mph speed limit except four, which had 20 mph speed limits. The speeds between humps is based on an average separation of 90m between the devices, with an 85th percentile speed of 26mph. Overall, the quality of this study is very poor . there is no methodological detail given, including any use of control sites, or before/after data collection periods. In the absence of other, specific analysis on round-top humps, this paper is used as a guide for effects on speed.
44% reduction in accidents is taken from Mountain, Hirst and Maher (2005). The study calculated accident reductions from various different types of traffic calming measures. Local authority and police data were used throughout Great Britain from 150 speed management schemes on 20 mph roads. Analysis is particularly strong, with correction for change in flow, accident trend and regression to mean.
Factors associating reduced motor vehicle speed to road safety are based around Wilson et al. (2010), who note the large body of research consistently linking casualty rate with speed (e.g. TRL 421).
References
Mountain, L., Hirst, W., Maher, M. (2005) Are speed enforcement cameras more effective than other speed management measures? The impact of speed management schemes on 30 mph roads. Accident analysis and prevention 37 pp. 742 . 754.
Taylor, M., Lyman, D., Baruya, A. (2000) The effects of drivers - speed on the frequency of road accidents (TRL421). Transport Research Laboratory. Crowthorne, UK.
Webster, D. & Layfield, R. (1996) Traffic calming - road hump schemes using 75mm high humps (TRL186). Transport Research Laboratory. Crowthorne, UK.
Wilson, C., Willis, C., Hendrikz, JK., Le Brocque, R., Bellamy, N. (2010) Speed cameras for the prevention of road traffic injuries and deaths (Review). The Cochrane Collaboration. John Wiley & Sons.
Winnett, M. & Wheeler, A. (2002) Vehicle-activates signs - a large scale evaluation (TRL548). Transport Research Laboratory. Crowthorne, UK.
