Adaptive signal control, transit signal priority, and intersection improvements implemented during the Atlanta Smart Corridor project produced a benefit-to-cost ratio ranging from 23.2:1 to 28.2:1.

Smart Corridor experience in Atlanta, Georgia

30 June 2010
US 41/Cobb Parkway/Northside Parkway; Atlanta; Georgia; United States

Summary Information

The Atlanta Smart Corridor project evaluated the implementation of SCATS (Sydney Coordinated Adaptive Traffic System) and Transit Signal Priority (TSP) as an integrated system designed to improve mobility, reduce emissions, and decrease the costs of delay and fuel consumption on an 8.2 mile section of US 41/Cobb Parkway/Northside Parkway located between the City of Marietta and Atlanta, Georgia. The project included three jurisdictions (City of Marietta, Cobb County, and City of Atlanta).

The project scope of work included the deployment of SCATS adaptive signal control hardware and software, TSP equipment, and presence detection (inductive loops and video detection cameras) at 18 intersections. In addition, new traffic signal controller cabinets, traffic signal heads, pedestrian signals, and pedestrian accommodations meeting ADA (Americans with Disabilities Act) standards were installed as needed.

Prior to the upgrade project, SCATS software was installed on a central server and made operational at the Cobb County TCC (Traffic Control Center). The City of Marietta and the City of Atlanta used regional computers to communicate with the Cobb County server and coordinate cross-jurisdictional control of adjacent traffic signals. TSP was enabled by modifying existing hardware and software used for emergency vehicle priority systems. In the City of Atlanta and Cobb County, additional upgrades were required at 15 intersections where two TSP detectors and a phase selector were installed at each intersection. All 60 CCT (Cobb Community Transit) buses were equipped with TSP emitters.


A before and after study was conducted to evaluate the effectiveness of both SCATS and TSP. For the SCATS study, travel time, delay, and stop statistics were recorded from probe vehicles traveling along the project corridor. The TSP study used riders to collect bus route timestamp and delay data at various bus stops and intersections on CCT Bus Route 10. Five (5) performance measures were evaluated, including: average travel time, standard deviation of average travel time, intersection stop rate, average intersection stop time, and on-time performance level of service.

Baseline data collection began in November 2009. After the system was implemented, tested, and accepted, post deployment data were collected in June 2010. Researchers examined normal peak period traffic flows (AM, Midday, and PM) in both directions of travel. Cost savings from reductions in vehicle stops were calculated by multiplying the average change in delay per vehicle for a peak period (AM, Midday, PM) between the "before" and "after" conditions by the two-hour traffic volume for that respective period, and then assuming there were 250 days per year with similar conditions, the annual delay benefit was estimated by the change in delay for the period multiplied by 250 days with a dollar value of $12 per hour and 1.2 occupants in each vehicle. This value accounted for the cost of delay and included the costs of wasted person time and vehicle operating costs.

Annual Delay Reduction Cost Savings = [(AM Change x 2 Hr Volume) + (Mid Day Change x 2 Hr Volume) + (PM Change x 2 Hr Volume)] x $12/Hr x 250 Days/Year x 1.2 Occupants/Vehicle

Fuel cost savings would also result from more constant travel speeds and fewer stops and idling on the corridor. The resulting benefit was calculated by multiplying the average change in the number of stops per vehicle for a peak period between the "before" and "after" conditions by the two-hour traffic volume for that respective period, multiplying the annual change in total stops for the period by 0.6 (in accordance with the AASHTO Manual on Road User Benefit Analysis) and then multiplying the calculated change in fuel consumption by the current fuel cost per gallon.

Annual Fuel Consumption Cost Savings = [(AM Change x 2 Hr Volume) + (Mid Day Change x 2 Hr Volume) + (PM Change x 2 Hr Volume)] x 0.6 x Current Fuel Cost/Gallon

Note, however, that the fuel savings calculated as a result of fewer stops, less idling, and more constant speeds would be offset slightly by the increased fuel consumption required to travel at higher speeds.


Overall, the system increased mobility and decreased fuel consumption.

Dividing the annual benefits to motorists ($5,938,646 from reduced travel time and fuel consumption) by the annual project cost ($210,584 to $254,547 depending on a capital investment interest rate ranging from 4 to 8 percent over a 10 year lifetime) the benefit-to-cost ratio ranged from 23.2:1 to 28.2:1.

The addition of SCATS and TSP had minimal impacts on transit level of service (LOS), however, based on the data collected researchers indicated that the biggest LOS improvement would come from ensuring that the buses did not leave the scheduled stops ahead of their scheduled departure time.

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Atlanta Smart Corridor Project Evaluation Report

Author: TransCore

Published By: Georgia Regional Transportation Authority

Prepared by TransCore for the Georgia Regional Transportation Authority

Source Date: 30 June 2010


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Benefit ID: 2011-00758