CHAPTER 5
Summary of Findings

This chapter summarizes key findings from the literature review, survey results, and case examples. Additionally, the chapter discusses knowledge gaps identified during the synthesis and suggests future research efforts to address these knowledge gaps.

Synthesis Findings

Overall, an increasing number of state DOTs are using SPM solutions (traditional ATSPMs, crowdsourced ATSPMs, or both) for proactive management and operation of traffic signals. The use of SPM solutions varies considerably among DOTs due to the varied challenges they experience. Key findings and takeaways from the synthesis are discussed in the following.

Deployment of SPM Solutions

Many DOTs use a combination of traditional and crowdsourced ATSPMs for management and operation of their signals. Approximately 83% of the responding DOTs (35 out of 42 responding) indicated that they use either traditional or crowdsourced ATSPMs. Approximately 45% of the DOTs (19 out of 42 responding) use only traditional ATSPMs, while approximately 5% of the DOTs (two out of 42 responding) use only crowdsourced ATSPMs. About 33% of the DOTs use both traditional and crowdsourced ATSPMs (14 out of 42 responding). Lastly, approximately 17% (seven out of 42 responding) reported that they do not use any SPM solution.

With regard to the scale of deployment of traditional ATSPMs, 18% of the DOTs (six out of 33 responding with some level of deployment of traditional ATSPMs) indicated full-scale deployment, 45% (15 out of 33 responding) reported moderate deployment, and 36% (12 out of 33 responding) reported limited deployment. Of the DOTs with limited deployment, 92% (11 out of 12 responding) reported that they have planned expansion in the future, and similarly, for those with moderate deployment, 87% (13 out of 15 responding) indicated planned expansions.

Regarding the scale of deployment of crowdsourced ATSPMs, approximately 13% of the DOTs (two out of 16 responding with some level of deployment of crowdsourced ATSPMs) stated full-scale deployment, 38% (6 out of 16 responding) reported moderate deployment, and 50% (eight out of 16 reporting) reported limited deployment. Nearly 70% of the DOTs (11 out of 16 reporting) indicated a planned expansion for crowdsourced ATSPMs.

Funding Sources

With regard to planning for the deployment of either traditional or crowdsourced ATSPMs, 37% of DOTs (13 out of 35 responding) indicated that their initial deployment was through pilot

projects, while 14% (five out of 35 responding) stated that they had conducted needs assessment prior to the deployment. For the initial deployment of traditional ATSPMs, with the option to select multiple answers, 79% of DOTs (26 out of 33 responding) reported the use of state funds, and 64% (21 out of 33 responding) reported the use of federal funds. When asked about funding resources to expand traditional ATSPMs, 79% of DOTs (26 out of 33 responding) reported using a combination of local, state, and federal funds, while 45% (15 out of 33 responding) reported dedicated budget allocations for technology upgrades, and approximately 24% (eight out of 33 responding) indicated grant-based funding.

SPM Solution Use Cases

Both traditional and crowdsourced ATSPMs can support a wide range of applications to improve signal operation and maintenance practices. Approximately 74% of the DOTs (26 out of 35 responding) reported that they use SPM solutions to handle public service calls and for making signal timing adjustments. Twenty-three out of 35 responding (66%) indicated the use of SPM solutions for evaluation of intersection operations and active traffic signal performance monitoring. Less than 10% of the DOTs (three out of 35 responding) reported that they use SPM solutions for multimodal operations analysis.

Of the 33 state DOTs using traditional ATSPMs, 78% reported reviewing ATSPM reports on an ad hoc basis for potential signal timing adjustments, while four DOTs (approximately 12%) reported conducting more routine reviews of ATSPM data (weekly or more frequently). Another finding was that, to identify issues related to infrastructure health, 13 DOTs (out of 33 responding, or approximately 39%) stated that they review traditional ATSPMs daily, which indicates a commitment to maintaining system reliability. Similar results were obtained for the crowdsourced ATSPMs, where 10 DOTs out of 16 responding (approximately 63%) reported ad hoc review for signal timing adjustments, and four (25%) reported weekly or more frequent review.

Finally, four reports provided by SPM solutions are found to be regularly used by state DOTs. These are Split Monitor (24 out of 35 reporting, or approximately 69%), Purdue Phase Termination (22 out of 35 reporting, or approximately 63%), Purdue Split Failure (20 out of 35 reporting, or approximately 57%), and Timing and Actuation (19 out of 35 reporting, or approximately 54%). Additionally, approximately 94% of the responding DOTs use traditional ATSPMs at the intersection level, while the use of traditional ATSPMs drops considerably at broader spatial levels: approximately 42% for corridor-level analysis and about 15% for network-level analysis. The use of crowdsourced ATSPMs, however, showed a more even distribution across spatial levels, with 88% of DOTs using them at the intersection level, 100% at the corridor level, and 50% at the network level.

Challenges and Experience Gained

Of the DOTs that have not fully deployed traditional ATSPMs but are planning to expand their use, almost all identified limited staff resources (23 out of 24 reporting, or approximately 96%) as the primary obstacle. The second most frequently stated response was outdated detection and signal controller technology (12 out of 24 reporting, or 50%). Similarly, of those DOTs that have not fully deployed crowdsourced ATSPMs but have planned expansions, the most common response was limited staff resources (eight out of 11 reporting, or approximately 73%). The second most frequently stated response was challenges during the adoption of new technologies (five out of 11 reporting, or approximately 45%). High up-front costs and ongoing maintenance were also identified as common challenges with crowdsourced ATSPMs (six out of 11 reporting, or approximately 55%). Note that in this context, maintenance relates to licensing fees.

The case examples showed that for most state DOTs, the full scale of deployment of traditional ATSPMs is vast, and taking a phased approach can help in progressively achieving full system integration. DOTs recognized that the process of learning and progressing with ATSPMs is a collective effort, and many DOTs are at different stages of ATSPM deployment, with some only in the pilot phase or just beginning.

Finally, the case examples highlighted the importance of strong leadership in overcoming these challenges by helping secure streamlined funding—for initial deployments, to maintain the system, and for expansions—and allocating appropriate staff resources.

Suggestions for Future Research

This synthesis study has also identified several potential areas for future research. It should be noted that, at the time of this writing, NCHRP Project 07-32, “Guide for Long-Term Automated Traffic Signal Performance Measurement Systems Applications,” was ongoing, and some of the suggestions outlined in the following may ultimately be addressed by that effort.

Gaps in Statewide Traffic Signal Management Practices

State DOTs manage traffic signals in varied ways, often without a unified strategy. Two key barriers to broader ATSPM adoption are:

• Challenges in establishing a unified statewide strategic framework for signal management and operations, and
• Limitations in obtaining sustained funding dedicated to traffic signal operations.

Large-scale and sustained implementations of traditional ATSPMs in Utah and Georgia suggest a clear pattern: DOTs in both states have long-standing commitments to centralized signal management and have reliable funding. This has enabled not only the maintenance of existing systems but also the ongoing upgrades and innovation that are necessary for SPM solutions. These examples highlight the need for further research into the policies and approaches that enabled these success stories. The research would offer valuable guidance for other DOTs seeking to strengthen their traffic signal management practices.

Integration of SPM Solutions into Business Processes

Most DOTs indicated that the primary barrier to adopting or expanding SPM solutions was limited staff capacity. Most DOTs indicated that access to quick, practical resources would help overcome challenges and support more effective use of these tools. These resources should have special emphasis on different ATSPM users, such as maintenance (technician or field) staff, traffic engineers, and traffic signal managers.

Once state DOT staff are familiar with ATSPM concepts and tools, there will be a need to develop formal procedures that align ATSPM use with broader traffic signal management goals and objectives. Establishing a clear, streamlined workflow for integrating performance measures into automated decision-making processes would further promote the adoption of SPM solutions into business processes.

Another opportunity for future work is the development of hands-on training materials that emphasize the integration of SPM solutions into DOTsʼ daily operations. Similar to quick reference guides, training materials should include content designed for various SPM users such as signal operations engineers, signal technicians, and managers and decision-makers. While a variety of training strategies have been used for SPM solutions by different states and the FHWA, most of

the training materials have traditionally focused on explaining the user interface and discussing the fundamentals of some of the common SPM reports.

Enhanced Multimodal Performance

Most state DOTs use SPM solutions (i.e., either traditional or crowdsourced ATSPMs) primarily to improve vehicle operations, and there is little attention given to pedestrians, cyclists, and transit vehicles. This practice is partly due to the limited metrics provided by SPM solutions and existing use, as shown by survey responses. While a few studies have explored leveraging SPM solutions for multimodal operations, these studies tend to be ad hoc and are not fully integrated into the UDOT open-source ATSPM software or most vendor products (note that the next version of the UDOT open-source ATSPM software will include some of the multimodal metrics).

Future research could explore several areas for expanding the multimodal capabilities of SPM solutions. One opportunity involves examining, under different signal phasing and timing strategies, the factors and risks associated with permitted conflicts between turning vehicles and vulnerable road users such as pedestrians and cyclists. These findings could help improve intersection safety while maintaining efficient vehicle operations. Another area of interest is the accurate measurement of vehicle speeds at intersections, which would help determine the prevalence of speeding and the conditions that contribute to it. Researchers could also study pedestrian crossing behavior using SPM data across various intersection types and signal timing strategies to identify factors that lead to unsafe or risky crossings. Finally, there is potential to develop new performance measures for transit operations and transit signal priority by combining traditional ATSPM data with other sources such as the General Transit Feed Specification Real-Time feed.

Automated Reports and System-Level Dashboards

The survey results and case example interviews revealed that most state DOTs use traditional ATSPMs for intersection-level analysis to identify maintenance-related issues or make local timing adjustments (e.g., splits and offsets). However, the DOTs raised concerns related to the use of traditional ATSPMs at the corridor or network level, in part due to the lack of aggregated charts or dashboards that can summarize key performance measures by corridor or network level. While a few DOTs (such as GDOT) have developed aggregated charts and dashboards (through the SigOps platform), and some vendors have these reporting capabilities, the UDOT open-source ATSPM platform is still missing these features. Limited staff resources exacerbate this issue because the limitations in automated tools require high levels of staff resources to examine each intersection individually.

Therefore, to increase the use of traditional ATSPMs and eliminate barriers to their widespread adoption, it is critical to develop automated reports, tools, and methods that can help practitioners identify hot spots at the movement, intersection, and corridor levels along with additional automated alerts (besides watchdog alerts) to flag operational issues or inefficiencies in the system. Additionally, providing built-in tools that aggregate traditional ATSPM data and enable system-level monitoring and decision-making is a crucial step toward facilitating broader adoption of traditional ATSPMs.