Sometimes getting a bad grade on an exam is precisely what a student needs to evaluate old habits and make necessary changes. For several cities in the United States, the results of the first National Traffic Signal Report Card (in which the average U.S. city received a grade of D-) inspired changes in the way they managed their traffic signals in order to reduce traffic delay for citizens and save operating costs
for the cities. The second version of the report card, which was released in 2007, showed moderate improvement. On average, cities moved up to a D rating, but several municipalities significantly improved by a couple letter grades.
After taking an initial self-assessment in 2005, the city of Alpharetta, Georgia revised its signal timings and reduced the number of vehicle stops by 23%, resulting in an 8% fuel savings and 17% reduction in trip times. Nashville, Tennessee achieved similar results and reported a benefit-cost ratio of 81 to 1. Other cities, such as Austin, Texas, first focused on maintenance, emphasizing preventative maintenance and cutting maintenance calls in half, which they were able to do without a budget increase. Plano, Texas reorganized its transportation engineering staff to reduce operating costs by more than $13 million over three years while eliminating 36 million vehicle stops.
The improvement process for all of these cities began with a self-assessment that evaluated traffic management staff organization. The cities also worked with key stakeholders such as law enforcement and emergency services, and took major sources of traffic surges, such as sports and entertainment venues, into consideration. To maximize the effectiveness of these sorts of assessments, the agency must understand:
- What type of data is currently being collected for monitoring and planning?
- How are signal timings currently set?
- Which arteries have the highest priorities?
- Which intersections have the highest crash rates?
By instituting a process to review individual signal timings and corridor timings at least every three years (more often if residential and business patterns change), a city using signal optimization software can identify adjustments it needs to make and how to best optimize the equipment that is already in place. Cities also need to develop plans that can be implemented quickly for special events and emergencies.
Monitoring traffic (and monitoring the monitoring equipment) is critical to optimizing traffic flow. When this data is made available to the public, it can encourage drivers to make smart routing decisions that reduce overall congestion. A variety of technologies are already available for monitoring traffic and adapting traffic signals on a real-time basis. Topeka, Kansas recently installed an adaptive traffic signal management system that adjusts for congestion and provides a “green light tunnel” for traffic on a major thoroughfare. This video puts the viewer in the driver’s seat of a vehicle cruising through seven consecutive green lights in a span of two minutes. Even if a city cannot afford to implement highly advanced technology, properly managing existing equipment and regularly reviewing signal timings can still yield substantial benefits to the city and its citizens.
A car idling at an intersection is basically running at zero miles per gallon. In addition, emissions increase as vehicles accelerate from a standstill. Conversely, maintaining a safe and smooth flow of traffic saves time, saves fuel, and reduces emissions. Cities of various sizes have demonstrated that investing time and resources into coordinated management of traffic signals pays off for the cities’ citizens and the environment.
Content for this Blog post courtesy of Michael Hilliard, Oak Ridge National Laboratory’s Center for Transportation Analysis