Results of a real-time, decentralized traffic signal system pilot test in Pittsburgh, PA.
Pittsburgh, Pennsylvania, United States
Real-Time Adaptive Traffic Signal Control for Urban Road Networks: The East Liberty Pilot Test
Summary Information
The Robotics Institute at Carnegie Mellon University (CMU) developed an adaptive traffic signal control system, SURTRAC (Scalable URban TRAffic Control), designed specifically for urban road networks, where there are multiple, competing dominant flows that shift dramatically based on time of day. This system is a decentralized system, where each signal independently determines its phasing based on incoming vehicle flows and projected outflows from neighboring signals.
In order to test this system, a pilot of nine intersections in the East Liberty area of Pittsburgh, Pennsylvania was equipped with this technology for a before and after study to analyze the difference in performance for the existing and SURTRAC systems. The test area has an average daily traffic volume of nearly 30,000 vehicles per weekday.
Methodology
To evaluate the SURTRAC system's performance, a series of timed, drive-through runs of the pilot test were conducted both under existing conditions and with the SURTRAC system enabled. The twelve highest volume routes through the East Liberty pilot test site were chosen for analysis. Tests were conducted for four weekday time periods -- AM-Rush, Midday, PM-Rush, and Evening -- in order to test the performance of the system in multiple conditions. "Before" testing was conducted in March 2012 and "after" testing was conducted in June 2012, with slightly higher (roughly 5%) traffic volumes in June.
Savings provided by the SURTRAC system were calculated by monetizing travelers' time, fuel consumption and pollution based on the assumed values in Table 8 below. These assumptions provide benefit estimates for the nine intersection test site at $7,184 daily and $1,875,127 annually (based on 261 weekdays). If the level of benefit remained constant as the system expanded to the 600 intersections in the City of Pittsburgh, annual city-wide benefits would be valued at over $125 million.
The pilot site capitalized on existing video detection capabilities at most of the intersections within the site to reduce costs. However, even if an assumed cost of $50,000 per intersection for technology upgrades is used, return on investment is realized after about three months of operation. Due to the system's decentralized nature, ongoing operational costs are considered negligible, as the system will self adjust to evolving traffic conditions over time. After five years of operations, a benefit-cost ratio of almost 20:1 would be expected.
| Parameters | Value | ||
| Value of Traveler Time | Cars | Trucks | |
12.75 ($/hour) | 21.25 ($/hour) | ||
| Value Occupancy | 1.59 | 1.0 | |
| Vehicle Split | 98% | 2% | |
| Gas Unit Price | 3.48 ($/gallon) | ||
| Pollutant Unit Price | CO | NOx | VOC |
0.0063 ($/kg) | 1.28 ($/kg) | 1.28 ($/kg) | |
