In August, Shaun Quayle, Customer Success Director for Public Sector Sales at INRIX, joined transportation professionals from the public and private sectors at the 2025 ITE Conference in Orlando to showcase INRIX mobility intelligence solutions.
During the event, Shaun Quayle and Justin Effinger, Practice Leader for TSMO: Arterial Management at Mead & Hunt, presented “Tales from the Wild: Proactive Signal Timing.”
In their presentation, they discussed INRIX Signal Analytics and GPS Probe-Based Signal Performance Measures (SPMs). By leveraging both Signal Analytics and SPMs, transportation professionals can gain real-time, data-driven insights without the need for costly roadside detection equipment.
From Vehicles to Actionable Insights
The process begins with GPS data from probe vehicles traveling through the network. This data is transformed into observed travel times and ultimately into signal performance metrics for both intersections and corridors.
The metrics for signalized intersections include:
- Travel Time
- Approach Speed
- Control Delay
- Level of Service
- Turn Ratios
- Observed INRIX Vehicle Trips
- 3+ Minute Delay
- Stops/AOG
- Time-Space Diagram
The metrics for corridors include:
- Travel Time
- Observed INRIX Vehicle Trips
- Travel Time Index
- Level of Travel Time Reliability
- Planning Time Index
- Free-Flow Travel Time
With nationwide traffic signal coverage agencies can track travel time, approach speed, control delay, level of service, turn ratios, travel time reliability, and free-flow conditions. These measures have been validated by pooled fund research across multiple DOTs which have confirmed the accuracy of GPS-CV signal performance measures. This enables agencies to systematically evaluate transportation infrastructure at scale—without the limitations of physical sensor systems.
Real-World Applications
GPS-based SPMs support a wide range of practical applications, including:
- Prioritized troubleshooting: Easily determines highest increase in delay, indicating a location to troubleshoot.
- Development review/traffic studies: Measured intersection and corridor performance measures to support development application review.
- Queuing analysis & model/simulation calibration: Detailed queuing patterns in trajectory plots. Speed, travel time, delay and other metrics to calibrate existing conditions model/simulation to measured reality.
- Before/after evaluation: Easy before/after evaluation of corridors and signalized intersections to fulfill project requirements.
- Construction traffic management: Monitor for operational changes. Rapid response or work zone mitigations.
- Progression analysis: Visually via time-space diagram trajectory plots.
- Adaptive signal control: Determine best candidates for adoptive signal control, inform system configuration, evaluate effectiveness, and support ASC management and operations.
- Transit Signal Priority: Analyze transit routes by movement at signalized intersections, determine impacts of various TSP strategies.
Transit Advantages of GPS-Based SPMs & Proactive Management
For transit agencies, GPS-based SPMs deliver key benefits:
- Streaming data and visualizations outside traffic equipment networks
- Evaluating competitiveness with auto travel
- Determine and measure TSP settings for maximum benefit
- Assess queuing for bypass lanes
Being more proactive in signal management helps increase mobility and safety. Automated daily email alerts flag abnormally high delays so agencies can act fast. These alerts also help detect stuck signal detection issues, broken communications, or contractor-related issues—keeping traffic moving safely and efficiently.
Moving Forward with Generative AI
Transportation-specific generative AI is the next leap. By combining congestion alerts, incidents, speeds, weather, and events into a foundation model, agencies can quickly answer questions about traffic causality and safety risks—identifying crash hotspots and suggesting proven countermeasures in seconds.
Case Studies & Nighttime Delay Detection
With nearly 950 traffic signals, Montgomery County uses INRIX Probe-Based SPMs and the RITIS platform for centralized monitoring. Before-and-after studies show clear improvements in arrivals on green and reduced delays—demonstrating the tangible benefits of data-driven signal management. DDOT piloted a study to evaluate three leading probe-based analytics platforms. The project tested accuracy, capabilities, and practicality for corridor and grid networks. This pilot provided crucial insights into how probe-based analytics can seamlessly integrate into daily traffic management, enhancing operational decision-making.
SPM data is also valuable for identifying detector issues during low-traffic hours. Comparing nighttime delays (midnight–5 AM) across months reveals patterns of malfunction, helping pinpoint where field inspections or repairs are needed. Intersections appearing at the top of the delay list for multiple timeframes are prime candidates for review.
Looking Ahead
GPS Probe-Based SPMs give agencies unprecedented visibility, accuracy, and agility in managing traffic signals. From spotting nighttime detector failures to optimizing large-scale networks, this technology empowers transportation professionals to make smarter, faster, and more effective decisions—delivering safer, smoother journeys for everyone. To learn more visit inrix.com/products/signal-analytics/ or watch our webinar on Unlocking the Power of Traffic Signal Performance Measures.