Delivering accurate bus information

John C. Toone, King County Metro, describes the transition to an IntelliDrive-led approach to communication and information sharing in line with the introduction of a new bus rapid transit service.

King County Metro (1792 KC Metro), which serves Seattle, Bellevue and over 20 suburban towns, has been active in the development of intelligent transportation systems for many years. It has operated a signpost-based AVL system for more than a decade and has used this to provide bus location information to the public on the Internet. KC Metro was also one of the first transit agencies in the US to develop a Transit Signal Priority (TSP) system. Its TSP deployment began operation in 2000 and there are now over 75 intersections in operation.

KC Metro will begin service on the first of five Bus Rapid Transit (BRT) corridors in 2010. Branded 'RapidRide', these will include familiar BRT features such as headway-based service, next bus arrival signs and off-board fare payment. At the same time, KC Metro is also deploying a completely integrated onboard system, a communication centre system, a radio network and a regional fare system. To support these ITS deployments, KC Metro has designed an ITS communications infrastructure based on the 324 US Department of Transportation's IntelliDrivesm concept.

Buses, signals, pylons and centres

Prior to the decision to create a BRT service, KC Metro undertook the enormous task of replacing all of its transit technology systems in an effort now known simply as the 'Big Three'. The Big Three includes replacing the Transit Radio System (TRS), replacing and integrating OnBoard Systems/Communication Centre Systems (OBS/CCS), and creating and integrating Smart Card, a regional fare integration project.

A key goal of the Big Three projects is to integrate the onboard technology environment. This includes an IP/Ethernet network with a wireless link for uploading and downloading operations data. The device originally specified for wireless communication was an 802.11 workgroup bridge. This device was sufficient for upload and download of transit operations data at the bus base. The later decision to create BRT service with ITS elements changed the requirement to include mobile wireless communications. KC Metro changed the specification to a 4.9GHz mobile router with a private onboard network for the CAD/AVL, fare box and security camera equipment.

At the roadside, KC Metro's ITS deployments will be clustered in two locations. Transit signal priority and 4.9GHz wireless access points will be located at the intersection. In a change from KC Metro's existing TSP installations, it will have separate ITS cabinets, or in some cases a separate space in the signal control cabinet. A 'stretch' cabinet was specifically designed for the RapidRide corridors in cooperation with the City of Seattle. Such cabinets have an upper space with separately keyed access. This allows KC Metro technicians to access ITS equipment without the need to coordinate with the local traffic jurisdiction. With a cable pass-through, the Transit Priority Request Generator (TPRG) resides in the top portion and communicates with the signal controller in the bottom portion.

For ITS applications at the major BRT stops, KC Metro has developed a 'Technology Pylon'. This structure holds the passenger information sign, showing the countdown arrival time of a BRT or regular service bus. It also holds an off-board fare processor. The pylon includes a wireless client and a wired switch so network connections to devices can be made with common Cat 5e cable. Other IP/Ethernet devices could be supported on this structure such as security cameras, voice annunciation and voice communication with customer service. In the future, KC Metro could deploy a modified version of these structures in downtown Seattle using mesh capabilities to avoid costly installation of new conduit.

Metro communication and control centres will have full-time communication to all ITS equipment and buses wherever the ITS network is deployed. This is achieved by creating a wired infrastructure from the King County WAN to the roadside. Backhaul is provided through either KC-owned fibre routes or by VLAN through partner jurisdictions. Washington State DOT is deploying a regional centre-to-centre network for exchanging video between local jurisdictions which KC Metro will use with its first two corridors. Through an agreement with the state KC Metro is using this network to connect directly to its corridors. That, or it is going through the local jurisdictions.

At the roadside, KC Metro is installing a fibre-optic network through agreements with the local traffic jurisdiction. In some cases it is installing new fibre and in others buying or using through agreement fibre from the city's traffic control network. This fibre will carry a gigabit Ethernet network throughout the RapidRide corridor. The value of partnering with the traffic jurisdiction is access to the signal control conduit. This reduces costs and provides communications to the signal cabinet.

A 4.9GHz wireless access point at the intersection, a 4.9GHz mobile router on board its vehicles and a wireless client at the RapidRide stations provide KC Metro's IntelliDrive network. KC Metro chose 4.9GHz for wireless communications because of the higher power output it allow and a strictly controlled wireless environment; a survey of its first RapidRide corridor revealed hundreds of 802.11 networks. Using 4.9GHz also provides an added level of security. The wireless network will provide up to 54Mb communications between vehicles and the roadside, including vehicle-to-vehicle and roadside 'last mile' communication. Table 1 shows the communications applications supported.

Vehicle-to-infrastructure TSP

King County Metro initially researched vehicle-to-roadside communications for TSP. Its current TSP system uses 900MHz RF tags on the buses with readers several hundred feet ahead of the intersection. A Transit Priority Request Generator (TPRG) located in the traffic signal cabinet processes the tag and requests priority from the signal controller when appropriate. The hardware and communications for this system are based on the technology prevalent in the traffic industry during the mid 1990s: x386 processors and serial communications. The tag readers are by far the costliest part of the system and require a great deal of coordination to mount, power and license. The opportunity presented by the onboard network was too tempting to pass up.

Through research, KC Metro found that Los Angeles had deployed a WiFi-based TSP system. LA had visited KC Metro several years before using the 560 ITS America Peer-to-Peer programme. KC Metro took advantage of the same programme and conducted a site visit to see how LA had successfully used WiFi for TSP. The key to its success was an architecture where each intersection was connected by a wired network backbone. That way, even when a bus loses a wireless connection it remains part of the network. LA also sent messages using UDP, and a 'fire and forget' messaging approach.

Architecture development

Using LA's experience, KC Metro began development of its new architecture. It built its core concept on the wired backbone and decided to use only fibre optics - partly because of the bandwidth required and partly to avoid working with aging copper wiring. During the development of the architecture, KC Metro also decided to replace the 802.11 work group bridge originally specified for wireless communications at the bus bases with a 4.9GHz mobile router. The router allows vehicles to be part of the KC WAN and yet only need to authenticate once per day. This allows vehicles to roam freely through roadside wireless networks with the only latency being the time taken to associate with an access point.

When voters approved RapidRide, the communication needs expanded and a comprehensive ITS architecture was required. Although development of its ITS architecture began narrowly as an upgrade to an existing 10 year-old TSP system, KC Metro eagerly moved to an open network concept. A general-use ITS infrastructure supporting a number of systems and types of communication would be much more powerful, flexible and cost-effective than numerous task-specific solutions. The IntelliDrive approach is a key component of this general-use network.

KC Metro's expectation is that its approach, using the IntelliDrive concept and an open IP/Ethernet network, will realise numerous benefits. Using a standard IP/Ethernet network has afforded access to many more networking solutions at prices driven by markets other than just ITS. Operations and maintenance costs will also be reduced by using the existing KC WAN infrastructure for network management. Future systems will be more easily integrated because of the ubiquity of IP/Ethernet devices.

Applications evolution

Using the IntelliDrive concept for communications around the roadside environment has also proven to be an enabling technology choice. The original intention was to achieve the transmission of TSP data from the bus to the signal controller. Using the concept of an open wireless network has been the solution to many issues that have arisen in the process of the Big Three projects and RapidRide ITS design, however. For example, the TRS allows the AVL system to poll a vehicle's location every 90 seconds. An IntelliDrive approach with an ITS architecture that connects vehicles to centres has over 1,000 times more bandwidth. Buses on the RapidRide corridors will update their position every few seconds allowing for very accurate location and bus arrival countdowns.

Another example of the utility of an IntelliDrive approach is security video. KC Metro's existing onboard security video programme is capable of allowing transit security police to stream video from the bus to an officer within line-of-sight using portable equipment. The new ITS network deployment will allow streaming of video from a bus on a RapidRide corridor to another vehicle on the corridor, or to the control centre. KC Metro's procurement for mobile routers includes the option to purchase routers for all transit police vehicles. So equipped, these vehicles will also have access to the KC WAN.

Beyond vehicles, a wireless environment in the corridor gives KC Metro far more flexibility of deployment for roadside devices. The civil engineering work involved in installing new conduit can be a significant capital cost. Wireless communications reduce the utility demand to just power, which can often be provided more easily. In downtown Seattle, KC Metro will be using this approach to retrofit the City's streetcar stations with fare card readers.

KC Metro's new architecture represents in many ways the future. The flexibility of an IntelliDrive wireless network, a fixed fibre backbone and high-bandwidth backhaul connections will connect vehicles, roadside equipment and communications centres on a single network. It demonstrates the increased operational effectiveness achievable with a modern-generation network solution with the ability to bring together numerous, previously discrete applications.

As of the writing of this article, King County is evaluating the proposals for the mobile router and is preparing to install the testbed at its training facility. King County has secured the required license to operate in the 4.9GHz frequency band in coordination with the regional body managing the 700MHz and 4.9GHz public safety frequencies. Integration testing will begin in the autumn/fall, while pilot testing will beginning the following summer on its first RapidRide corridor. The remaining four corridors will be deployed over the next three years.

Table 1: Communications supported by the KC Transit ITS network

System	Communications	Centre to:	Roadside to:	Vehicle to:
Transit Signal Priority (TSP)	Priority request, configuration, management, logs	Roadside	Roadside, Centre	Roadside, Centre
Real-time information signs (next bus arrival)	Vehicle location, next bus arrival message	Roadside	Centren Customer	Centre
Fare processing	Transactions, management	Roadside	Centre
Onboard security cameras	Video			Vehicle, Centre