With an increasing number of organisations heading down the ‘digital highway’, it was really only a matter of time before highways operators themselves woke up to the new digital age of network connectivity.
In the UK this process is well under way, in the shape of a 10-year project aimed at providing a national digital system linking more than 14,000 message signs, emergency telephones, CCTV and traffic monitoring systems to the English Highways Agency’s control centre network.
Known as the National Road Telecommunications Services (NRTS) project, the GB pound 490 million upgrade will use Internet-based technology to support advanced roadside services and new initiatives, such as access to real-time video pictures of traffic conditions via the web.
As it currently stands, the agency provides voice, video and data telecommunications services through such devices as matrix signals indicating speed and lane restrictions, emergency roadside telephones and CCTV cameras. All these devices are operated on behalf of the Highways Agency by around 30 police forces throughout the country. Devices are connected to a series of small structures known as a transmission stations via the agency’s own local copper cable, or fibre optic cables in the case of the cameras. These stations are typically up to 80km away from control rooms, so devices are connected, in turn, via trunk transmission networks, which interconnect a chain of transmission stations spaced up to 20km apart.
Streamlining the service
The NRTS contract was won by a consortium called GeneSys Telecommunications. It replaces a large number of existing contracts that have built up in a piecemeal fashion over the past 40 years. Partly as a consequence of this fragmented network of contracts, little use has been made of the topology of the road network to provide diverse routes for telecommunications services. The trunk networks operate over fibre or copper cables and use a variety of technologies to suit the needs of each type of service. Hence, it was often the case that a control room area could have two or three trunk networks. This unfortunate scenario was exacerbated by the fact that neighbouring areas also had their own trunk networks, so there was little interconnection between neighbouring control rooms.
Indeed, the seeds of the project were borne out of a study undertaken by the agency to investigate its future telecommunications requirements and how they could be best procured. It highlighted the following inefficiencies in the current network:
The NRTS project was also influenced by another study to investigate the future role and responsibilities of the agency and the police with respect to managing the trunk road network. This study suggested that the 30 control rooms should be consolidated into seven regional control centres.
Resilient against risk
The decision to rationalise the multitude of control rooms into seven created a need for a network that could provide greater resilience and support disaster recovery strategies, with IP deemed the mode of choice. David Bradbrook, NRT operations team leader, explains: “We’re putting more eggs into fewer baskets. So, for example, if a regional control centre went down, there would have been the risk of losing hundreds or thousands of phones.”
By employing an IP network, the agency will benefit in the future from back-up operations, with transmission stations and control centres meshed to provide multiple paths between locations. So, if part of the network goes down, the system re-routes the traffic via an alternative path. Likewise, if there is a loss of a control system, then provided the working system in a neighbouring control centre ‘knows’ the IP addresses of the devices, it can take over control of the roadside devices in that area. IP’s ‘anywhere to anywhere’ capability should thus provide the agency with the tools to respond more effectively to changes in boundaries, working patterns and seasonal peaks. The first phase of network configuration, which will allow the new control centres to work with the current control room systems, is close to completion. The next stage is to make everything compatible with the NRTS network and this is being rolled out at the various regional centres between now and January 2007.
Sharing images
Demand has also been growing to support new types of services and customer, such as the need to connect ANPR and speed enforcement cameras over the network, as well as transmitting video-feeds to interested third parties. Bradbrook explains: “It’s not just us that want to view the images; the BBC and travel information providers want to use them too.” The agency’s Video Information Highway Initiative, a set of principles governing how the agency shares video, should help to achieve this ambition.
It allows a variety of users, including police operators, agency employees and representatives, to select any available camera connected and gain real-time camera control, preset control and remote-viewing facilities. Described by Mark Sharp, project manager for CCTV equipment development, as a shrink-wrap piece of software installed on a PC, the system also allows third-party commercial organisations with an interest in travel information to view the pictures, “as long as the PC has an interface to the NRTS network”.
Shared images are compressed as MPEG4 and can be sent at various speeds: 128Kb/s, 256Kb/s, 2Mb/s and 4Mb/s. Automatic or manual blocking systems guard against the distribution of sensitive images to other parties, such as in the case of a gruesome accident, a lone female or visible number-plates.
The IP approach adopted for the project will also support multicasting – a technique likely to be used for the distribution of images where two or more regional control centres wish to view the same camera. According to Bradbrook, IP multicasting splits, or replicates, a data stream at the point in the network closest to a control centre, in order to ensure the best possible use of bandwidth. This allows for huge bandwidth savings compared to current techniques, where pictures are typically brought into one control office and then re-transmitted to a neighbouring office. Images are compressed using MPEG2 and are transmitted at 12-15Mb/sec, while the practice of sending only ‘I’ frames causes less distortion than sending the whole picture, as it minimises the real-time delay.
In addition, IP’s ability to support traffic prioritisation via MPLS (Multi-Packet Layer Switching) was also a factor, as effective management of the roads network demands reliable access to real-time information.
Overcoming challenges
But using IP for real-time CCTV is not without its problems. Despite the savings being made on bandwidth, operators in control of the motorway systems require broadcast quality images with pan, tilt and zoom controls, which place an overwhelming demand on the IP system. The agency has determined that an acceptable round-trip delay when controlling a camera is 250 milliseconds. But the problem of achieving this is exacerbated when the means of controlling this delay falls across more than one contractor, i.e. the provider of the transmission and the provider of the camera control equipment.
But there are other ways to enhance real-time image transmission. On an urban motorway, for example, where gantries are closely spaced and dense with devices, it is possible to create a local network using Ethernet switches located at each of the gantries and interconnected over fibre cables. The agency is currently trialling this arrangement on the M42 motorway around Birmingham, where gantries are 500m apart and fitted with signals, variable messaging signs, incident detection systems and enforcement and surveillance cameras – all of which will have IP interfaces. The switches will be shared between a number of fibres to reduce the latency of the network and increase the resilience.
Extending IP to the roadside on rural motorways presented further challenges. One problem is that there are a large quantity of legacy devices which use the agency’s own proprietary protocols, carried using RS485 dc line driver circuits. To overcome the need to overhaul all such legacy equipment, the agency is integrating the protocols with the IP system by using the network to carry the analogue signals back to a regional control centre. This approach uses DSL technology to extend the IP network to the point where the IP-to-RS485 conversion takes place. In future, however, the agency will procure all new devices with Ethernet and RS485 interfaces, to allow IP to be extended to the roadside device without the need for any conversion of legacy protocols.
Video will be fed to the nearest transmission station as a multiplexed, uncompressed digital signal over fibre. There, the signals will be demultiplexed and then encoded to provide an IP data stream between 2Mbps and 15Mbps, depending on the required picture quality. Emergency roadside phones will be connected to voice-over-IP gateways that convert speech to IP packets. These could be deployed in environmentally hardened roadside cabinets or transmission stations. Here, digital recording systems with around 7Tb of disk space will record images at 25fps for a certain period, after which they will move to a new buffer at reduced picture quality for easy storage. With their ability to extract lower-quality images from higher-quality ones, the DVRs will also provide video-feeds to a web server at around two frames every second, for access by relevant and authorised third parties.
A vision of connectivity
In a further development, the agency is also investigating the potential deployment of network cameras, possibly using wireless technology to provide a low-cost solution to certain situations, such as providing temporary coverage during road works. And the police have also asked the Department for Transport for a commitment to the sharing of ANPR data and are awaiting a decision.
Ultimately, when complete, the Highways Agency’s roadside IP network will provide one of the largest real-time, IP-based video surveillance networks in the world, with over 900 cameras spread over 3500km, all with ‘anywhere to anywhere’ connectivity. The smart roads era is about to get into gear.
