city of Philadelphia's new traffic control system, The

Institute of Transportation Engineers. ITE Journal, Jun 2002 by Kaiser, Dean J, Montanez, Richard

Many municipalities have implemented traffic control systems in an effort to efficiently monitor traffic conditions, manage incidents and provide the optimum degree of congestion-reducing parameters associated with system technology. In this second feature in a series on Philadelphia, PA, USA-the site of the ITE 2002 Annual Meeting and Exhibit-- the authors provide an overview of the City of Philadelphia's new traffic control system and some lessons learned during the lengthy analysis period and through construction completion and implementation of that technology.

PROJECT BACKGROUND

In 1991, the fifth largest city in the United States had nearly 3,100 intersections controlled by traffic signals of varying ages. Signal installation started back in 1923 with over one-third of the signals being installed during the 1950s. The Traffic Engineering Division of the City of Philadelphia's Department of Streets was able to modernize approximately 25 percent of the oldest electromechanical controllers since 1975 at a rate of approximately one per week. In addition, various city, state and federal projects led to several individual and corridor-wide traffic signal upgrades.

The upgrades during that period still called for the installation of electromechanical controllers to operate the traffic signals. Corridor traffic signals were interconnected via seven-conductor interconnect cable to field-located master electromechanical controllers, which were left to synchronize the corridor signals on their own; no centralized control system was in place to help monitor any of the traffic signals within the city.

In late 1970, a signalization system was implemented in a point-to-point configuration with a "central" controller monitoring the reconstructed system in the downtown central business district (Center City). Operations and maintenance were not key components to the system and within a short period, interconnection cable was severed by ongoing utility work in the area and, ultimately, was abandoned during the 1990s.

The start of the last decade of the 20th century found the city ready to take stock of its transportation system and move forward with innovative traffic control solutions that various communities across the United States had been implementing at a rapid rate. A multitude of traffic-engineering initiatives were implemented within the city, which contributed to accident reductions and the American Automobile Association's recognition for pedestrian initiatives.

The various nonsignal-oriented initiatives included an increase in all-way-stop-- controlled intersections, accident-record retention, and school-zone parking clearances and signing. Several signal-related initiatives included recalculating and implementing signal clearance intervals (all-red interval), providing optimum pedestrian visibility and an adherence to the simplest efficient signal operation (limiting specialized multiple phasings).

These initiatives still did not address the growing concern of the operations and maintenance of the 3,100 traffic signals. It was determined that much of the major highways leading into and out of the central business district had undergone significant improvements geometrically while several key internal Center City areas were also upgraded, thereby seeing new traffic circulation patterns within the region.

Current state and national policies1 emphasized the reduction of congestion and delay. City officials began to focus on a solution to the problem within Center City by optimizing the traffic signal control operations. The Center City Signal Improvement Project represented a significant upgrading to the existing system for the purpose of achieving the goals.

In the heart of Center City is the city's Municipal Services Building (MSB), locale of nearly all city operations and personnel and over 10 percent of the total traffic signals within the city. The Traffic Engineering Division is located on the ninth floor and was considered the appropriate location of the centralized control center. Figure 1 illustrates the existing Center City traffic signal system layout. Not to overextend itself, the city, along with the local traffic-consulting firm of Orth-Rodgers & Associates Inc., initially decided to limit the size and scope of the system design to the southwestern quadrant of Center City. The proximity to MSB and size of the quadrant (82 intersections) would give the city the ability to determine all its needs within a manageable test area should problems arise with system startup. All system control hardware, software and intersection equipment would be upgraded and implemented, and the system would be readily expandable to enable control of the rest of Center City and, ultimately, the entire city.

FEASIBILITY STUDY

A feasibility study detailing the existing system, the modernization project Is goals and objectives, the procurement and implementation procedures, and an operations and maintenance plan had to be submitted and approved by the Federal Highway Administration (FHWA)2 as a requirement of funding. The final report was submitted in August 19923 with an addendum in December 19964 detailing the revised communications system to be implemented. Key personnel within the city contributed to the determination of the system and equipment components, including the former Deputy Commissioner of the Department of Streets, the Chief Traffic Engineer and various other engineering services personnel, including engineering design, signal maintenance, operations, construction, highways and street lighting.