MÉTODOS COMPLEMENTARIOS:

VAS are part of a range of measures currently used internationally to curb vehicle speeds, similar to measures like speed cameras, Variable Message Signs (VMS) and conventional traffic calming devices like speed humps.

Research that compares measures like VAS, speed cameras and conventional traffic calming devices in terms of their effectiveness and / or feasibility could not be identified or sourced to add value to this research. The assumption is therefore made that such research may not exist.

VAS have been proven technically effective and economically feasible to reduce vehicle speeds, prevent road traffic crashes and improve road safety in the County of Surrey (Surrey County Council, 2010), which supports speed management as an intervention identified in the Global Plan for the Decade of Action for Road Safety 2011 – 2020 to ultimately create a safe road transport system (World Health Organisation, 2011).

2.2.1 OVERVIEW

VAS are roadside electronic signs that display a message when they are activated by a sensor that has detected a vehicle, typically, exceeding the speed limit or exceeding the safe

travel speed (based on road geometry) on a section of road, especially when approaching a hazardous condition, for example a sharp bend or intersection.

VAS is a form of technology that combines information and communication technology with transport infrastructure, and it is therefore classified as a form of Intelligent Transportation System (ITS) technology.

VAS are used in locations where conventional road signage alone may be ineffective in reducing vehicle speeds or warn drivers of a specific hazard, for example in high crash risk locations VAS can act as a supplementary measure to add emphasis to or improve visibility of the conventional sign. VAS reduce the risk of road traffic crashes occurring through visual interaction with drivers, thus simultaneously improving road safety for all road users in the immediate area.

VAS are also used to protect road infrastructure by warning drivers of inappropriate vertical clearances or weight limitations applicable to the type of vehicle they are driving. An overheight vehicle detection system at a bridge, as shown in the following figure, is an example of such a system that utilises VAS technology. The focus of this research is however on the use of VAS to reduce vehicle speeds.

Figure 2-4: Overheight Vehicle VAS

(Source: Dambach UK Ltd, n.d.)

From a functional point of view, VAS are distinctly different from electronic VMS, since these two sign types have different modes of operation and application. VMS tend to be larger in size and usually display a changeable information message to motorists, as shown in Figure 2-5. These signs normally form part of a network of signs linked to a traffic control room where operators use the VMS to inform or control traffic on the relevant roads.

Section 2.4.2, South Africa, elaborates further on the typical uses of VMS in relation to VAS, as well as the legislation regulating the use of these signs on public roads in South Africa.

Figure 2-5: Variable Message Sign

(Source: Swarco Traffic Ltd, 2013)

The following information has been summarised from the VAS Good Practice Guide (Surrey County Council, 2009) prepared by Surrey Country Council in the United Kingdom. This guide is considered to provide a good general overview of how VAS can be applied.

2.2.2 VAS TYPES AND PURPOSE

VAS are normally used to encourage a driver to reduce speed by displaying an advisory message, typically ‘Slow Down’, together with a relevant speed limit or warning sign. The use of flashing lights, referred to as wig-wags in the United Kingdom, is optional but recommended in order to draw a driver’s attention. The text message and flashing lights are normally amber in colour.

Table 2-8 presents the typical VAS types and their purposes.

VAS also have the ability to perform traffic surveys as a secondary function through the use of an optional built-in traffic detection radar, which collects constant traffic data (time, date, speed) that are downloadable.

Table 2-8: Typical VAS Types and Purpose

VAS Type Purpose Typical Example

Speed Regulatory Sign

Speed Enforcing: Used to encourage a driver to

reduce speed by displaying a specific message, for example

‘Slow Down’ together with the speed limit.

Warning Sign

Warning of a Hazard: Used to warn drivers of a speed camera ahead if they are exceeding the speed limit,

or to display other messages and warning signs relating to road safety, for example sharp

bend or intersection ahead.

(Source: Surrey County Council, 2009)

2.2.3 SIGN OPERATION

Sign activation is triggered once a vehicle has been detected travelling in excess of the programmable speed limit set within the sign. Vehicle speed detection is optimised by the use of a microwave vehicle detector normally placed on the top of the sign, but it can also be housed inside the sign face. The signal generated can activate a ‘delay-on’ timer (delaying the illumination of the warning message for a few seconds) but normally the sign activates immediately illuminating the warning message and flashing lights (wig-wags) if fitted.

2.2.4 TYPES OF VAS SITES

VAS are used for the following types of site installations:  Permanent – Large size VAS on signpost.

 Semi-permanent – Medium size VAS on signpost. Used on site for 4 to 6 months at a time, but can be left for as long as required.

 Temporary – Small size VAS on signpost or street lighting pole. Used for short periods of at least 1 month.

 Mobile – Mini size VAS on signpost or street lighting column. Used for short periods. This type also include small / medium / large size VAS fitted to ‘A’-frames, car roofs,

trailers or truck beds, powered by a vehicle, battery, solar or generator. Ideal for roadworks sites, special events or at schools with frequent speeding problems.

VAS are used on all road types, for example national roads, arterial roads, collector roads and local streets, including single and dual carriageway roads.

2.2.5 POWER SUPPLIES

VAS utilise the following power supplies:

 Electrical feed – Power is taken from the nearest electrical supply, which is often a street lighting column.

 Solar – Power is taken from the sun via a solar panel, which is installed on top of the VAS unit. Internal batteries are charged by this system during the day and thereafter used at night.

 Wind – Power is taken from wind energy via a turbine, which is installed on top of the VAS unit. Internal batteries are charged by this system and used when there is little or no wind.

 Battery – Power is taken from a rechargeable battery pack situated inside the VAS. 2.2.6 BENEFITS

The various types of VAS all have different benefits:

 Effectiveness – Some reports and case studies carried out in the United Kingdom have shown that where VAS are used an average speed reduction of 10-15% and an average injury reduction of 30% were achieved (Surrey County Council, 2009). A more detailed discussion regarding the effectiveness of VAS is included in Chapter 3, Methodology, and Chapter 4, Results and Discussions.

 Traffic Calming – Temporary small and mobile mini VAS can be moved from site to site and are a quick, inexpensive and effective way of dealing with speeding problems and crashes caused by excessive speed. This reduces the need for other traffic calming measures like speed humps or rumble bumps, and is therefore considered to be a cost saving measure.

 Traffic Data – Permanent VAS sites can provide constant traffic data, which can be analysed to identify trends and monitor the effectiveness of the permanent installation. The cost of collecting traffic data via a VAS is considered cheaper than obtaining traffic data via a conventional traffic survey company.

 Financial – In the United Kingdom, the cost saving as a result of the reduced number and severity of road traffic crashes has been proven to outweigh VAS installation and maintenance costs.

 Environmental – Steadier vehicle speeds help to lower fuel consumption and thus decrease emissions. Lower vehicle speeds also create a less intimidating environment for vulnerable road users like pedestrians and cyclists.

2.2.7 CONCERNS AND PROBLEMS

Some drivers think that if you activate a VAS then you will be fined in the same way as a speed camera. This is not the case, although some VAS are installed in advance of speed cameras and give the driver the chance to slow down if they are exceeding the speed limit. If a VAS is installed for this purpose it will typically display a speed camera symbol either on its own or with the speed limit.

VAS could increase sign clutter along roads if installed in addition to existing road signage. VAS should therefore be used selectively and be well positioned on site to avoid sign clutter. In areas where a high concentration of signage is present, the existing signage should be reviewed in order to reduce sign clutter prior to the installation of a VAS.

Vandalism may occur to the sign face, speed detection radar or solar panel (if fitted). VAS should therefore not be installed in areas considered to be at high risk of vandalism.

2.2.8 MAINTENANCE

The regular maintenance of VAS is necessary to ensure the signs operate effectively, which normally forms part of the initial product warranties offered by VAS manufacturers. VAS manufacturers also tend to offer maintenance contracts at a fee upon expiry of the initial warranty period, which is typically two years.

It is considered good practice to inspect VAS at least once every 6 months in order to maintain the effectiveness of these signs. Problems caused by passing vehicles, dirt and foliage can be avoided by carefully selecting VAS sites, the verge position and mounting height.

Typical checks that are carried out at installed VAS are:

 Microwave vehicle detector head (if present) must be clean and have unobstructed view of the detection location,

 Signface must be clean and correctly aligned to give approaching vehicles an optimal view of the sign,

 All foliage in proximity of the sign must be trimmed back to ensure VAS detect approaching vehicles correctly.

2.3 USE OF VEHICLE ACTIVATED SIGNS BY SURREY COUNTY COUNCIL