A Primer on Automated Traffic Signal Performance Measures

Harnessing this data offers tremendous opportunity to improve movement through intersections, and to address safety concerns based on real-time and highly specific data. Continue reading to learn:

• Why we should care about ATSPMs as transportation professionals;
• The four steps of collecting and using ATSPMs; and
• The guidance that’s being written to help agencies do this effectively.

Why Should We Care About Automated Traffic Signal Performance Measures?

ATSPMs bring many benefits to agencies. As detailed in the NCDOT Guide on Automated Traffic Signal Performance Measures, ATSPMS make it possible for agencies to:

• Manage traffic signals more proactively. Traffic signal timing engineers often spend a considerable amount of time calibrating models to existing conditions before evaluating signal timing adjustments. Through ATSPMs, we can measure performance instead of predicting it.
• Receive more comprehensive information. Without recording real-time data, most agencies rely on turning movement counts collected over a few days during the year. We plug these volumes into a model to estimate what is happening – emphasis on “estimate.” In contrast, through using ATSPMs, we can collect data 24 hours a day over months or even years, and adjust to what’s going on.
• Make data-driven decisions. Having months of continuously collected data will lead to better-informed signal timing adjustments and help agencies allocate resources effectively.
• Identify high-priority locations. Signal timing engineers can spend less time troubleshooting because ATSPMs can specifically pinpoint malfunctioning equipment. In addition, automated alerts can bring issues to the surface before public service requests are received.

While the process of gathering, transferring, and interpreting these performance measures is absolutely “easier said than done,” we can think about it in four main steps.

Step 1: Record Time-Stamped Data

At every intersection, a controller tells the signal when to change. If there are detectors installed, the presence of vehicles and pedestrians influences the signal timing.

At intersections using the latest models of traffic controllers, we can record when vehicles go over the detectors, when pedestrians are detected, and when the lights change at a tenth of a second intervals. Through combining these pieces of time-stamped data, we can learn quite a bit about how the intersection is operating. For example, are drivers waiting long? Are pedestrians waiting long? Are vehicles stopping often?

Step 2: Move Data Where It Can Be Processed

The high-resolution signal data can be transmitted from the intersection to a centralized database where data from multiple intersections over extended periods of time can be stored. Getting that data from the field to the office is complex because of security protocols and the physical infrastructure (such as fiber) required to connect equipment in the field to a central location.

While many consultants know how to use the data once it’s centrally stored, we at Kittelson enjoy the challenge of making the process work in the background – helping agencies move their data to a place where they can use it. Network engineering is important for agencies that want to own the data themselves.

Step 3: Interpret The Data

Once you have pulled off successful communication from the intersection to a centralized database, it’s time to make sense of the data. High-resolution data is stored in an unprocessed format, and database software is needed to normalize the data. Different types of ATSPM software are available to process the data, calculate metrics, and produce visual reports for staff and public consumption.

Step 4: Do Something With Your Data

ATSPMs open many doors for agencies. Of course, data is only as good as what you can do with it. ATSPMs give us powerful information that can be used to improve safety and efficiency of signalized intersections to improve people’s safety and experience. This includes the safety and experience of non-motorized users.

Here are some of the ways that various stakeholder groups can use ATSPMs:

• Traffic signal timing engineers and technicians can use ATSPMs to determine signal timing changes, make equipment repairs and pinpointed locations, and conduct before-and-after studies.
• Managers can establish a routine process for checking automated alerts and use ATSPMs to prioritize project locations for signal retiming and equipment repairs.
• Policy makers can use cost/benefit information to evaluate current investments and program future investments.
• Transportation planners and designers can access ongoing volume reports to inform designs.

We are completing work with support from researchers at Purdue University on NCHRP 03-122, a guidance document that will explain the requirements for an ATSPM system, how to interpret common performance measures, and how ATSPMs can change day-to-day traffic signal system management for the better. This guidebook is scheduled to be released in early 2020 and we are excited for the value agencies will gather from it.

There’s Much More to Talk About

This is the first article in a series about tapping into the potential of ATSPMs to make data-driven decisions at signalized intersections. Future installments of this series will cover:

• What it takes to get to statewide deployment of ATSPMs;
• More on what agencies can do with ATSPMs; and
• How agencies can get the most value out of guidance document NCHRP 03-122.

In addition, you can reference the NCDOT Guide on Automated Traffic Signal Performance Measures for more detail on each of the steps described in this article.

We’re passionate about this topic, and always up for a lively discussion. Feel free to reach out to either of us to talk further!