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Methodology

This documentation explains how TES calculates key values in the Speed Radar Board. Understanding these terms and formulas will help you interpret speeding risk and site rankings more effectively.

🧭 What Is the Goal of This Module?​

The Speed Radar Board in TES is designed to help municipalities and road safety teams identify areas where speeding is a concern and prioritize locations for intervention.

By using radar speed data, traffic volume, and historical collision patterns, TES produces a risk score for each site. This allows decision-makers to:

  • Understand driver behavior across different roads and intersections
  • Detect patterns of excessive speeding
  • Link those patterns to collision risk
  • Prioritize sites for speed mitigation (e.g. signage, enforcement, redesign)

The goal is to use data-driven methods to rank locations so that limited safety resources can be deployed where they’re most needed.

⚙️ How It Works: Metrics and Calculations​

TES uses three primary data sources:

  • Speed Study Data – How fast vehicles are driving at a location
  • Traffic Volume (AADT) – How many vehicles are using the road daily
  • Collision History – Where crashes, especially aggressive ones, are occurring

Each metric is standardized (normalized) to ensure fair comparison across all sites.

🛣️ Speed Metrics (Driver Behavior)​

These describe how vehicles behave at a given site:

MetricDefinition / How It’s Calculated
Speed AverageMean speed of all vehicles recorded.
85th Percentile SpeedThe speed below which 85% of vehicles are traveling. Commonly used in road design.
Compliance(Number of vehicles at or below the speed limit ÷ Total vehicles) × 100
Posted SpeedThe legal speed limit for that road segment.
Min of PaceThe lower bound of the 10 km/h speed range with the highest number of vehicles.
Max of PaceThe upper bound of that same range.
Pace Percentage(Number of vehicles in pace range ÷ Total vehicles) × 100
Total AADTAverage number of vehicles using the road per day over a year.

📐Distance from Speed Limit​

Distance from Speed Limit measures how far the average driver speed (represented by the Min of Pace) deviates from the posted speed limit. This metric highlights how excessive the speeding is at a location.

Distance from Speed Limit = (Min of Pace – Posted Speed) ÷ Posted Speed

While some drivers may exceed the speed limit slightly, large deviations suggest more aggressive or dangerous behavior. A higher distance value indicates more severe speeding, which can contribute to crash risk.

📊 Normalized Traffic AADT​

To compare volume across all locations, each site's AADT is divided by the highest AADT observed in the study:

Normalized AADT = AADT at site ÷ Maximum AADT across all sites

This gives a value between 0 and 1, indicating relative traffic volume.

🚨 Incompliance​

Incompliance measures the proportion of drivers who exceed the posted speed limit at a given site. This is a key indicator of road user behavior and helps flag areas where speeding is common and enforcement may be needed.

Incompliance = 1 – Compliance

A higher incompliance value suggests a greater share of drivers are not respecting the speed limit, and thus the site may present a higher safety risk.

🚧 Collision Risk Metrics​

TES uses both overall collisions and aggressive collisions to capture the danger associated with speeding.

Normalized Collision Rate​

To compare crash levels across sites:

Normalized Collision Rate = Total Collisions at site ÷ Highest number of collisions at any site

Normalized Aggressive Collision Rate​

Same idea, but only using aggressive collisions:

Normalized Aggressive Collisions = Aggressive Collisions at site ÷ Highest aggressive collisions across all sites

🧮 Final Site Score Calculation​

TES creates a final score that combines all of the above to estimate the safety concern at each site:

Score = Distance from Speed Limit + (0.1 × Normalized AADT) + Incompliance + (0.1 × Normalized Collisions) + Normalized Aggressive Collisions

Each component has a specific purpose:

  • Distance → Indicates how excessive speeding is

  • Volume → Captures exposure (more drivers = greater risk)

  • Incompliance → Measures driver disregard for speed limits

  • Collisions → Reflect real-world consequences

  • Aggressive Collisions → Capture severity and danger

🥇 Ranking and Prioritization​

Once each site’s score is calculated, TES ranks all sites:

  • Higher scores = Higher concern and higher risk

  • Lower scores = Safer, more compliant sites

This ranking helps municipalities:

  • Visualize high-risk areas

  • Track compliance improvements over time

  • Allocate resources more efficiently (e.g., placing speed boards, redesigning roads, increasing enforcement)