Vehicle-activated Signs (VAS)
Vehicle-activated signs (VASs) are an electronic sign which only become visible when approaching motor vehicles are exceeding a certain speed.
The signs normally display the speed limit, however they can also warn drivers of an approaching hazard (e.g. a bend).
VASs are formed of many bright lights which only turn on when the target motor vehicle is in plain view of the sign.
Disadvantages
- Not as effective as vertical interventions
- Too many vehicle-activated signs could diminish their effectiveness
Restrictions
- Vehicle-activated signs must be placed on a straight stretch of road to allow the radar device to accurately judge the speed of approaching motor vehicles
There's also some general restrictions to note for all schemes
Advantages
- No discomfort or delay experienced by any vehicle user
- Relatively cheap
- Continue to have a positive effect over time
- Can be installed where there is no electricity connection (using solar power and batteries)
Effectiveness
Accidents
Vehicle-activated signs reduce accidents by approximately 31%. This means they are very similar to horizontal treatments in their effectiveness. Specifically for roads with lower speed limits (30 or 40 mph), Vehicle-activated signs have shown increased effectiveness, and reduced accidents by 34%.
Speeds
For this section, research has split Vehicle-activated signs into two categories; roundel signs, which show the speed limit; and warning signs, which advise of an upcoming bend or junction.
Roundel signs on 30 mph roads have reduced motor vehicle speeds between 2.6 to 7.1 mph. The amount of motorists exceeding the speed limit dropped by 18 to 34 percentage points.
The effect of a warning sign is more variable. In a built-up area with a 30mph speed limit, a junction warning sign can be expected to reduce motor vehicle speeds by approximately 7%.
Time
Research has examined if VASs still have a positive effect on driver behaviour after one year of installation. It was found the signs still maintained their positive effects.
Bristol 20 mph
The information here isn't based on any data from roads which had a 20 mph speed limit. Bristol is currently working towards introducing a 20 mph limit on most roads, excluding some strategic roads.
The information here provides a good indication of what could be expected when a VAS is used on a 20mph road . it's very likely motor vehicle speeds, and accidents will reduce significantly.
Advanced information
Accidents for all types of Vehicle-Activated Sign
Accident reduction figures are from a medium quality study from TRL into VASs (Winnett & Wheeler, 2002). Whilst the study examined VASs at a range of locations using before/after methodology, a detailed analysis was carried out in Norfolk at 21 VAS sites using a modelling technique based on eleven years accident data (1990-2000). To reach the above figures accident reduction figures, the model predicted the number of accidents within Norfolk if no VASs had been installed, compared with the observed number of accidents with the VASs. This methodology should provide a reasonably accurate indication of safety effects, however there is no explicit implementation of long term trend correction for accidents which may offset effects by a small, but significant amount.
Speeds at Vehicle-activated roundel signs
Similarly, vehicle speeds at speed limit roundel signs are based on the same TRL study (Winnett & Wheeler, 2002). The methodology is of medium strength . the data were collected using a covert and accurate technique over a long time period, however there was a small variance in distance between data collection and the VASs. Data were collected before sign installation, within one month after installation, and after one year. Overall the data provides a strong indication of VAS effects, despite some flaws.
Speeds at Vehicle-activated Junction warning signs
Speed at vehicle activated warning signs is based on a good quality simulator research study into speed reducing treatments (Jamson et al., 2010). The research specifically compared UK treatments on UK style roads. The research findings are considered to be very conservative, as the study only recruited young (19 to 25 years old) male drivers - younger drivers, and specifically young male drivers are most likely to be speeding, therefore research which is found to be effective on this group is thought to be at least equally effective on other vehicle users. A speed reduction of 7% may be greater across an average cross section of drivers.
Of the sites studied in Winnett and Wheeler, only one was applicable to Vehicle activated warning signs in a 30 mph limit area. This constitutes poor evidence, however the result was consistent with the above research from Jamson et al. (2010). Evidence from other sites were excluded as they were at roads with 60 or 70 mph limits, which is unlikely to be applicable for Bristol.
Speeds at Vehicle-activated bend warning signs
This information was not included, as only one site with a 30 mph speed limit with a bend warning sign was available in the Winnett and Wheeler study.
References
Jamson, S., Lai, F., Jamson, H. (2010) Driving simulators for robust comparisons: A case study evaluating road safety engineering treatments. Accident Analysis and Prevention 42 pp. 961 . 971.
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.
Winnett, M. & Wheeler, A. (2002) Vehicle-activates signs - a large scale evaluation (TRL548). Transport Research Laboratory. Crowthorne, UK.
