Crash Rate Calculator

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Traffic Crash Rate Calculator

Please enter valid positive numbers for all fields.
Calculated Crash Rate
0.00 RMEV

Based on 0 crashes over 0 years.

Understanding Traffic Crash Rate Analysis

The Crash Rate Calculator is an essential tool for traffic engineers, urban planners, and safety analysts. Unlike simple crash frequency (the raw count of accidents), a crash rate normalizes accident data against traffic exposure. This allows for an objective comparison between different intersections or road segments regardless of how much traffic they handle.

Why Calculate Crash Rates?

Calculating the crash rate helps identify "hot spots" or high-risk locations that warrant safety improvements. By factoring in the volume of traffic (exposure), engineers can determine if a high number of crashes is due to dangerous road geometry or simply a result of very high traffic volume.

Method 1: Intersection Crash Rate (RMEV)

For intersections, spots, or specific nodes, the standard metric is Rate per Million Entering Vehicles (RMEV). This formula calculates the frequency of crashes for every one million vehicles that enter the intersection.

The Formula:

  • R = (C × 1,000,000) / (V × 365 × N)

Where:

  • R = Crash Rate (RMEV)
  • C = Total number of crashes in the study period
  • V = Traffic Volume (AADT – Average Annual Daily Traffic) entering the intersection
  • N = Number of years of data

Method 2: Road Segment Crash Rate (RMVM)

For stretches of highway or road segments, the standard metric is Rate per 100 Million Vehicle Miles (RMVM). This takes into account not just the volume of traffic, but the length of the road segment being analyzed.

The Formula:

  • R = (C × 100,000,000) / (V × 365 × N × L)

Where:

  • R = Crash Rate (RMVM)
  • C = Total number of crashes
  • V = Traffic Volume (AADT)
  • N = Number of years
  • L = Length of the road segment in miles

Interpreting the Results

Once calculated, the crash rate is often compared to the Critical Rate or the statewide average for similar facility types. If the calculated rate exceeds the critical rate, the location is statistically significant for having a safety issue that may require countermeasures such as signal timing adjustments, improved signage, or geometric reconstruction.

Example Calculation

Imagine an intersection with 15 crashes over a 3-year period. The Average Annual Daily Traffic (AADT) is 25,000 vehicles.

Using the RMEV formula:

  1. Multiply crashes by 1,000,000: 15 × 1,000,000 = 15,000,000
  2. Calculate total exposure: 25,000 × 365 × 3 = 27,375,000 entering vehicles
  3. Divide: 15,000,000 / 27,375,000 = 0.55 RMEV

This means there are roughly 0.55 crashes for every million vehicles entering this intersection.

function toggleFields() { var method = document.querySelector('input[name="calcMethod"]:checked').value; var lengthContainer = document.getElementById('lengthContainer'); if (method === 'segment') { lengthContainer.style.display = 'block'; } else { lengthContainer.style.display = 'none'; document.getElementById('length').value = "; // Reset length if hiding } // Hide result when switching modes to encourage recalculation document.getElementById('resultBox').style.display = 'none'; } function calculateCrashRate() { // Get Inputs var crashes = document.getElementById('crashes').value; var years = document.getElementById('years').value; var aadt = document.getElementById('aadt').value; var method = document.querySelector('input[name="calcMethod"]:checked').value; var errorMsg = document.getElementById('errorMsg'); var resultBox = document.getElementById('resultBox'); // Validation if (crashes === "" || years === "" || aadt === "" || crashes < 0 || years <= 0 || aadt <= 0) { errorMsg.style.display = 'block'; resultBox.style.display = 'none'; return; } var c = parseFloat(crashes); var n = parseFloat(years); var v = parseFloat(aadt); var rate = 0; var unit = ""; // Calculation Logic if (method === 'intersection') { // Formula: (C * 1,000,000) / (V * 365 * N) var numerator = c * 1000000; var denominator = v * 365 * n; if (denominator === 0) { errorMsg.innerText = "Traffic volume and years must be greater than 0."; errorMsg.style.display = 'block'; return; } rate = numerator / denominator; unit = "RMEV (per Million Entering Vehicles)"; } else { // Segment Logic var length = document.getElementById('length').value; if (length === "" || length <= 0) { errorMsg.innerText = "Please enter a valid Segment Length in miles."; errorMsg.style.display = 'block'; resultBox.style.display = 'none'; return; } var l = parseFloat(length); // Formula: (C * 100,000,000) / (V * 365 * N * L) var numerator = c * 100000000; var denominator = v * 365 * n * l; if (denominator === 0) { errorMsg.innerText = "Inputs cannot result in zero division."; errorMsg.style.display = 'block'; return; } rate = numerator / denominator; unit = "RMVM (per 100 Million Vehicle Miles)"; } // Display Results errorMsg.style.display = 'none'; resultBox.style.display = 'block'; document.getElementById('rateResult').innerHTML = rate.toFixed(2) + ' ' + unit + ''; document.getElementById('summaryCrashes').innerText = c; document.getElementById('summaryYears').innerText = n; }

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