David Crawford investigates traffic signal priority initiatives developing for better bus travel on the US Pacific Coast
Transit patronage rises by an average of 35% along commuter corridors equipped with bus rapid transit (BRT) systems, according to the US Department of Transportation’s Federal Transit Administration (FTA).
BRT as defined as bus transit enhanced with ITS systems for better services, is winning new passengers attracted by opportunity to avoid increasing fuel costs and traffic congestion. BRT brings signal delay reductions of up to 4%, and travel time reductions of upwards of four minutes – enough to qualify as successes by FTA criteria.
With some 50 BRT schemes now operational or planned across the US, there has been a corresponding growth in demand for traffic signal priority (TSP) technology, previously installed largely for emergency vehicle preemption (EVP) to boost safety and response times. TSP can significantly improve bus transit operations, but there are initial cost implications.
Solutions are emerging to address the problem of initial costs. On the US West Coast, for example, California Partners for Advanced Transportation Technology (PATH) is looking for commercial partners to exploit what is claimed as a cost reducing adaptive transit signal priority (ATSP) and dynamic passenger information (DPI) scheme. This involves using existing automatic vehicle location (AVL) systems to provide additional signal priority capability and so avoid installation of extra equipment on buses or streets.
The ATSP and DPI scheme envisages a combination of AVL and advanced communication system (ACS) technologies with common on-board units, vehicle location information and communications with road infrastructure, using GPS locating.
California PATH’s initiative reflects concerns that despite systems sharing both hardware and software, and having critical elements already in place, they tend in practice to be separately implemented. This can result in multiple units needing to be installed on each bus, costing transit agencies millions of dollars of unnecessary investment in equipment.
The 33-month California PATH project has now delivered an open system architecture designed to integrate ATSP/DPI with existing AVL/ACS systems, with layered database structures, processing modules and interfaces for data collection and information dissemination. California PATH claims that its database is both flexible and scalable.
Field testing at 50 ATSP enabled intersections along a 16km stretch of the El Camino Real corridor south of San Francisco with two equipped San Mateo County Transit District buses, has demonstrated scope for reducing travel times by 4.4% and increasing bus running speeds by 4.3% – meeting FTA success criteria – as well as cutting total intersection delays by 19.4%. As a result, California PATH has concluded that there is “great potential” for its planned integration.
In researching the concept, California PATH looked at existing TSP systems already running in the San Francisco Bay area, including that of Alameda-Contra Costa Transit (AC Transit) which operates on the eastern side of the bay.
AC Transit currently uses infrared communications between buses and individual traffic signal controllers to activate TSP at signalised intersections. Around 40 of its 500 strong fleet are currently equipped with infrared Opticom transmitters, as originally supplied by Minnesota-based Global Traffic Technologies (GTT) which in 2002 introduced a GPS and radio- based alternative.
This takes into account the fact that infrared TSP is limited to line of sight operation. Many US cities have problematic intersections where a bend in the road or an incline obstructs the line of sight to the signal. Additionally, a transit agency may want to plan a new route that will need TSP activation around corners.
The Opticom TSP control system
In a GPS/radio system, on-board devices calculate vehicle speed, direction and positioning data, while equipment at intersections is programmed with an approach map that defines corridors for both transit (TSP) and emergency (EVP) vehicle control. As the vehicle enters the intersection’s radio range, it sends updated speed, position and identification information, as well as turn signal status, once a second.
The intersection equipment then sends a priority request to a phase selector in the controller cabinet, which requests a green light through normal controller functions. (The system also recognises activated turn signals and relays the priority call forward to the next appropriate intersection).
AC Transit’s buses ply routes that have around 140 signalled intersections fitted with the GTT’s infrared solution which the agency is responsible for installing on behalf of its planning and funding entity, the Alameda County Transportation Commission. AC Transit is now planning a major upgrade to take advantage of GTT’s Opticom Multimode solution. Launched in June 2011 to deliver interoperability between infrared and GPS/radio priority control, Opticom Multimode uses signal phase selectors that can recognise both and deliver coordinated results to traffic controllers.
The effect is that GPS/radio-based TSP can be implemented where it is needed without demanding retrofitting of intersections where infrared priority control is in place. GTT chief executive officer Doug Roberts says: “Now municipalities can keep their existing Opticom infrared systems and upgrade only at problem intersections where transition to GPS/radio makes most sense. In the past, such transition would have meant complete replacement of infrared equipment, putting a significant cost burden on the municipality.”
Created in 1986, the multi-disciplinary California PATH programme is run by the Institute of Transportation Studies at the University of California, Berkeley, in collaboration with the California Department of Transportation (Caltrans). Its role is to research and develop innovative solutions to the state’s surface transport problems. In 2011, it merged with the California Center for Innovative Transportation.The Alameda-Contra Costa upgrade will be incorporated into the Interstate 80 (I-80) Integrated Corridor Mobility (ICM) project currently in progress. On the transit side, this involves installing 40 GPS/radio units on buses run by AC Transit and another operator, Western Contra Costa Transit (WCCT), with 32 intersections to be equipped with Opticom Multimode.
The north-south I-80 highway crosses nine cities – including Oakland and Berkeley – each with their own infrared equipped intersections and EVP or TSP infrastructures between the Bay and Carquinez Bridges in Alameda and Contra Costa counties. For some years, I-80 has ranked worst in the Bay area for levels of peak period traffic congestion.
With no room for further road expansion, the Contra Costa Transportation Authority (CCTA) concluded more effective management of the current transportation system, including transit, was the only practical means for adding capacity. The ICM project requires AC Transit and WCCT to share routes equipped with both infrared and GPS controlled intersections in the northern part of the corridor. Multimode is being installed to deliver the necessary integration.
GTT was formed in 2007 from 3M’s ITS business. Its Opticom technology is currently in use at over 70,000 intersections worldwide. It first introduced GPS/radio-based priority control in 2002, with a ‘third generation’ launch due soon. Infrared control, first introduced in the 1970, is currently in its fourth generation. Opticom Multimode won the Minnesota High Tech Association’s 2011 Tekne Award in the most innovative electronic device category.Doug Roberts says: “Meeting the I-80 requirement could have involved equipping intersections with non-compatible technologies from multiple manufacturers. That would have doubled the amount of equipment needed and so the costs.”
The system’s central management software provides desktop access to operational status and system reports, with capability for updating system attributes and troubleshooting. In a major emergency, it can switch to evacuation mode and instruct all TSP fitted intersections to recognise all equipped vehicles as qualifying for preemption for a fixed period, allowing buses to operate as though they were EVP equipped with the ability to demand (instead of request) a green light.
GTT stresses that it considers infrared, with its extensive installed base, to be a ‘workhorse’ system that will continue for many years to come. Roberts says: “One of our core design mandates is to preserve backwards compatibility both within and across technologies to maximise customers’ leverage of their installed base.”But GTT is also looking to wider horizons: “Today municipalities are working to build interoperable regional EVP and TSP systems within and across city lines because citizens do not see the boundaries,” Roberts adds. “Our aim is to deliver citywide, regional and national compatibility and savings.”
Source: ITS International’s website (February 2012)
