In 2008, the project team was tasked by the South African Minister of Transport to develop a Freeway Management System (FMS) for the City of Cape Town. The FMS was not only to be fully deployed and tested by June 2010 for the Soccer World Cup (SWC), but should also have offered a comprehensive solution realizing all the benefits of a FMS. The benefits of FMS's such as improved incident management, faster response times, improved traffic flows, improved travel times and the delivery of real time information to the public are well documented. The focus of the FMS project was to ensure that these benefits can be realised for the people of Cape Town and to role the solution out within budget and within the very tight time constraints.
The extent of the freeway network over which the management system was to be deployed covers more than 150 km and included most of the major freeways in and around Cape Town. The design solution required included the deployment of more than 190 CCTV cameras and 48 VMS’s which were linked together with networking equipment and a fibre optic network for communications. Where a fibre optic network was not available or could not feasibly be installed, use was made of wireless direct radio links. The cameras are mostly PTZ cameras mounted at a height of 13 to 15 metres on galvanized steel poles. The VMS are mostly cantilevered side mounted with only one mounted on a gantry on an elevated freeway. The VMS signs are 3-line signs with 7 pixel high by 90 pixel wide amber LED display boards, allowing 15 characters per line.
The freeways traverse densely developed urban areas as well as unpopulated rural areas with some sections of the freeway along elevated viaducts. Some of the major challenges that had to be overcome during the design and construction phase included the following:
- The availability of power at remote camera and VMS sites.
- The infeasibility of trenching through some of the built-up areas.
- The prevalence of theft and vandalism of electrical cables.
- Delays of electricity connection applications to the different authorities.
- Construction activities along some freeways preventing the installation of ducts and cables.
- Strong winds, windless periods and cloudy days.
The use and application of renewable energy (solar and wind) to power camera and VMS sites ensured timeous delivery of a sustainable and comprehensive network solution which was operational for the 2010 SWC and has ever since been used intensively to manage the Cape Town freeways.
It is not evident if this solution has been implemented anywhere else in the world to the same extent as in Cape Town, but is at least the only installation of its kind in South Africa. The design, construction and operational experience of this solution open up many rural applications for freeway and roadway management, for example at dangerous mountain passes, busy rural intersections and at remote weighbridges.
Renewable Energy Solutions not only allowed extensive and full CCTV coverage of the freeway network, but also allowed for strategic positioning of all VMS's. These included the most remote locations.
The effectiveness of a FMS depends on the timeous detection of incidents, i.e. the extent of visual coverage of the network and the ability to inform the travelling public when and if necessary, i.e. the location of VMS’s. With the necessary technology in place the FMS personnel can provide an optimum service to the travelling public. In Cape Town the full benefits of an FMS would not have been possible without the use of the renewable energy installations.
It was infeasible to provide full CCTV surveillance coverage of the required freeway network and to install VMS’s in the strategic positions without the use of renewable energy sources. To provide power to many camera and VMS sites were either impossible due to physical constraints or cost prohibitive. Apart from the actual cost of trenching and cabling, the prevalence of theft of copper cables in South Africa hiked the cost of the cable installations since all electrical cabling had to be encased in concrete.
Based on the total cost of cabling, trenching and connection fees, a distance of 1 km was used as the decision point of whether mains power is supplied to the camera or VMS site or if renewable energy is used.
The use of renewable energy sources ensured that a very important milestone of the Cape Town FMS Project could be met, i.e. the 2010 Soccer World Cup Event.
In just more than a year, the project team had to plan, design, implement, test and commission a FMS along more than 150 km of freeways under the jurisdiction of three roads authorities (City of Cape Town, Provincial Government of the Western Cape and the South African National Roads Agency) while several other construction contracts were running on the same roadways and where electricity is supplied by, at least two suppliers. There was not control room in place, no communication network, not protocols and no agreements between the different authorities. The extremely high focus on all projects to be completed before the world cup absorbed many officials with many other tasks and this was not helped by the effects of the property/development boom and the need for electricity by many other developments. During this period the ability of the national energy provider (ESKOM) to deliver sustainable mains power was tested and in many cases they could not respond to the demand with rolling black outs as a result.
The project team had to work extremely closely, not only with all the relevant authorities, but also with at least four other construction managers responsible for other contracts along the freeways. Apart from the affordability of bringing mains power to FMS CCTV and VMS sites, many sites were within construction zones which simply did not allow for the installation of cables and or any ducting until the completion of the projects. Renewal energy supply ensured that in these locations the FMS system could be installed without relying on any ducting or mains supply. Communications were effected through wireless radio links.
The workload and limited resources of the power supplying agencies did not allow for the timeous approval of wayleave applications and connections to the mains supply. In some cases, the project team had to resort to the use of renewal energy.
Providing a cost effective solution using a reliable renewable energy supply which is independent of the mains supply, theft and vandalism of cables.
The electricity consumption of the FMS cameras and the VMS’s are relatively low, typically less than 200W. The power consumption of VMS’s is minimal when there are no messages displayed on the sign.
The cost of providing mains supply through cables to camera and VMS sites was one factor which determined when/where renewable energy was to be used. The actual decision factors that were used to determine whether a site was a candidate for renewable energy were the following:
- Where municipal or ESKOM supplies were not available.
- If the distance from the nearest supply exceeded 1km.
- Where electricity supply was delayed by red tape.
- Where supply or the installation were delayed by other construction projects.
The total installation cost of the renewal equipment per camera location or VMS installation amounts to approximately R40 000 (US$6 000) which is comparable to the cost of laying an electrical cable, encasing it in concrete for 1 km and connecting it to the mains supply. In many locations along the route, the provision of renewable energy resulted in significant savings to the project.
The saving in the electricity consumption cost did not feature in the decision of the use of renewable energy. This possible saving of approximately R2 000 per year per camera site is comparable to the replacement cost of the batteries every two years. This is not a convincing argument for a sustainable solution, but the main factor in determination of the requirement of the renewable sites was the capital cost of the installation. The renewable equipment on the poles are susceptible to vandalism and crime, but to a lesser extent due to the mounting heights. For additional security the solar panels are all equipped with a satellite tracking device which is activated the moment the panel is moved away from its normal position. In the event of theft, the panels can be recovered.
The technologies chosen for the renewable energy sites are a combination of solar and wind. Cape Town has dry windy and sunny days in summer, but extended periods of wet weather in winter with little wind, but the weather could also be accompanied by strong, sometimes gale force winds.
Each site is equipped with a single 300 to 400W wind turbine plus 2 (camera sites) to 4 (VMS sites) 165W solar panels.
A few lessons learnt were:
- A design autonomy time of 2 days was insufficient, and additional batteries were added.
- Some sites were unsuitable for wind turbines due to strong winds, which damaged the turbines and turbines and turbine blades had to be re-designed.
- Shedding part of the load, such as switching off cameras at night, helped extend the autonomy time.