Percent Reduction in Estimated Vehicular Travel Time in Corridors and Intersections Studied
This measure focuses on traveler benefits derived from the Austin Transportation Department (ATD) retiming signals along synchronized arterial streets. Travel time is a crucial indicator of how traffic flows along city streets, which is also related to levels of fuel consumption and related air pollutants. Today, ATD operates and maintains over 1,000 signals. ATD’s goal is to evaluate and retime one-third of the signals annually.
This measure is calculated by collecting travel times along the synchronized arterials before any timing changes were made. This data, along with field observations, is used to adjust the signal timing. After all changes are made, travel time data is recollected. The percent reduction between the before and after travel times represents the average travel time savings travelers could experience when traveling the arterial during the AM, PM, and midday peak periods.
FY 2015-16 Results
In FY 2015-16, travel times along the corridors were reduced by 12.1%, 7.1% above the established goal.
Assessment of Results
In FY 2015-16, ATD evaluated and retimed 214 signals along 16 corridors. The nationally-recommended practice is to re-evaluate signal timing at each signal at least once every three years, which results in re-evaluating 1/3 of the signals each year, or in the City of Austin’s case, approximately 333 signals per year. ATD had four signal engineers on staff during the year, but were unable to devote full-time resources to signal re-timing, due to other duties, projects, and special responsibilities, including staffing the City’s Traffic Management Center. In April 2016, the City hired a consulting firm, to staff the Traffic Management Center, which freed up the City’s signal engineers to devote more time to re-timing efforts.
ATD will increase signal timing funding by adding an additional staff position to assist with signal retiming efforts. The additional staff position will help ATD meet the national recommendation of re-evaluating signal timing every three years. In addition, this position will allow ATD to place additional resources on signal timing projects related to construction and special event activity.
ATD continues the conversion to a more advanced and innovative signal control system. This technology approach will facilitate updating signal timing plans, responding to citizen requests more rapidly, and identifying system problems (e.g., detection issues) before the public is aware of them.
ATD continues to investigate a new key performance indicator that measures the overall effect of signal timing changes for all roadway users. Currently, the reduction in signal timing shows a percent reduction in travel time for automobiles, however, there is a direct unmeasured improvement for other modes of transportation, such as buses. As a result, ATD is working with CapMetro, in order to develop and optimize a plan for signals to feature Transit Signal Priority, which should particular reduce travel times for buses.
Lastly, ATD continues to deploy travel time sensors to allow continuous measurement of both travel time and reliability of travel times along major arterials at all times of the day and not only during the peak period. As a result, a more comprehensive and accurate assessment of signal retiming performance can be performed.
For more information contact Robert Spillar, Transportation Director at (512) 974-2488.