Signal Performance Metrics

This is part 2 of 4 in our blog series on Traffic Insights. This post covers Signal Performance Metrics. Stay tuned for more!

In part one of this series, we covered the evolution of data-driven traffic operations. We looked at the obstacles many cities face in implementing modern systems. And we didn’t forget to cover the benefits:

1. Better payback from infrastructure investments and 2. Better served citizens.

Both are driven mainly by the traffic insights available from Spectrum.

These insights fall into three main categories: Signal Performance Metrics (the subject of this blog post), Arterial Performance Metrics, and Maintenance and Infrastructure (which we will cover in future posts).

Design, tune and troubleshoot with SPMs

Signal Performance Metrics (SPMs) are a set of measurements and visualizations that help traffic teams design, tune, and troubleshoot traffic intersections. They are part of Miovision Spectrum, a turnkey solution for remote traffic signal optimization.

Spectrum provides the entire range of solutions needed to collect, monitor, and understand traffic signals. This includes a managed cellular connection and tools for signal monitoring, video streaming, maintenance alerts, and traffic data insights.

Spectrum’s analytical tools and reports generate actionable information from the raw traffic intersection data. SPMs provide intersection-level reporting of key metrics like:

  • Vehicle volumes
  • Wait times
  • Problem detection

Do these questions ring true?

If you recognize the questions below, your team is a good candidate to test these solutions.

SPMs help traffic agencies answer the most basic questions like:

  • Are my traffic signals working?
  • What kind of traffic volumes are we seeing?

But also deeper-level questions like:

  • Do we have an appropriate allocation of green time between movements?
  • Are we meeting our goals on vehicle wait times at rush hour?

How are SPMs generated?

Spectrum captures event data from the traffic controller, detectors, and other cabinet devices. This data includes signal state, pre-emption, and detector actuations. This is generated from stop-bar and upstream count detectors and pedestrian call button actuations.

Spectrum’s cabinet hardware is able to generate this data even from cabinets housing older traffic controllers. These typically do not produce high resolution reporting. The raw data is securely stored in Spectrum’s cloud where analysis is performed to extract meaningful information and actionable insights.

screen-shot-2016-11-14-at-9-45-34-am

What are the infrastructure requirements for Signal Performance Measures?

Although Spectrum Traffic Insights can be useful in an intersection with no detection, the set of available analytics expands with additional detector infrastructure.

With no detectors, Spectrum SPMs include:

  • Red/Green Allocation: The proportion of green time allocated to each approach and movement.
  • Pre-emption Summary: Reports of pre-emption events, durations, and triggers, including railroad crossings or emergency vehicle pre-empts.

With stop-bar detection data, Spectrum SPMs include:

  • Red and Green Occupancy Ratio: Gauges the demand for the various phases based on the ratio of time that vehicles are present in the associated movements. This allows for tuning of split times between phases.
  • Purdue Split Failure: Industry-standard metric that charts the frequency of split failure occurrences, an incident where green signal time fails to meet the vehicle volume demand.
  • Simple Delay: Simplified approach delay measures the time between detector activation during red singals and movement service at start of green signals. Simple delay approximates the overall delay experienced by intersection users.

With advanced upstream detection, Spectrum SPMs include:

  • Arrival Volumes: Counts of total vehicle traffic through an intersection from each approach.
  • Arrivals-on-Red vs. Arrival-on-Green: Counts of total vehicle volume arriving during red or green, giving a rough sign of progression quality for the given movement.
  • Purdue Coordination Diagram: A graphical representation of individual vehicle arrivals relative to cycle time (red, yellow and green), highlighting arrival characteristics, and platoon progression quality.
  • Average Delay: The length of time vehicles are delayed at a congested intersection.

What do SPM dashboards and reports look like?

We’ve included three screen grabs for dashboards that are generated by Spectrum.

The UX is designed to 1. Be as simple as possible for a big data set and 2. Show performance patterns over time.

Check these out!

Approach Volume: chart showing the volumes for the chosen day compared to the previous 12-week weekday average and variability bands.

approach-volume-pg11

Arrivals on Red/Green over a 12-week period showing the average volume of traffic arriving at the intersection during the red or green phases at different times of the day.

arrivals-on-red-pg11

Occupancy Ratio chart showing the stop bar occupancy ratio during red, green, and the first 5 seconds of subsequent red (ROR5) for each cycle of a selected movement.

occupancy-ratio-pg12-1

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Feeling informed? Part three of this blog series will appear in two weeks. It will cover Miovision Traffic Insights for Arterial Performance Metrics.