Calculator Inputs
Example Data Table
| Site | Mode | Years | Total Crashes | AADT / Entering Vehicles | Length | Crash Rate |
|---|---|---|---|---|---|---|
| North Connector | Road Segment | 1 | 18 | 14,500 | 2.4 | 1.4174 |
| Central Junction | Intersection | 3 | 29 | 32,000 | — | 0.8276 |
| Industrial Loop | Road Segment | 2 | 11 | 8,900 | 1.2 | 1.4123 |
Formula Used
Road segment crash rate: Crash Rate = (Crashes × Multiplier) ÷ (AADT × Segment Length × 365 × Years)
Intersection crash rate: Crash Rate = (Crashes × Multiplier) ÷ (Entering Vehicles × 365 × Years)
Severity weighted value: EPDO = (Fatal × Fatal Weight) + (Injury × Injury Weight) + (PDO × PDO Weight)
EPDO rate: EPDO Rate = (EPDO × Multiplier) ÷ Exposure
Approximate interval: Rate ± (Confidence Factor × Standard Error), where Standard Error = √Crashes × Multiplier ÷ Exposure
How to Use This Calculator
Choose a site type first. Use road segment mode for linear corridors, intersection mode for junction analysis, and custom mode for alternate exposure bases.
Enter total crashes for the study period, then split them into fatal, injury, and property-damage-only values. Keep the category sum equal to total crashes.
Provide exposure inputs such as AADT, segment length, or entering vehicles. Adjust the multiplier to match your preferred engineering reporting standard.
Set severity weights if your agency uses EPDO analysis. Submit the form to view normalized rates, severity share, annual average crashes, and an interval estimate.
Use the export buttons after calculation to download the visible result table as CSV or save the result summary as a PDF.
FAQs
1. What does crash rate measure?
Crash rate measures crash frequency after adjusting for traffic exposure. It helps compare sites with different traffic volumes, lengths, or study periods more fairly.
2. When should I use road segment mode?
Use road segment mode when crashes occur along a measurable corridor. It combines AADT, segment length, days, and years to normalize crash experience.
3. When is intersection mode better?
Intersection mode suits junction analysis where entering vehicles represent exposure better than route length. It is often used for signalized and unsignalized intersection safety studies.
4. What is EPDO?
EPDO means equivalent property damage only. It converts crash severities into one weighted score so locations with fewer but more severe crashes stand out.
5. Why include a confidence range?
A confidence range shows the uncertainty around the estimated crash rate. It is helpful when screening sites or checking whether apparent differences may be random.
6. What multiplier should I enter?
Common practice uses 100,000,000 for road segment vehicle-mile exposure and 1,000,000 for entering-vehicle intersection exposure. Choose the value matching your reporting convention.
7. Should severity counts equal total crashes?
Yes. Fatal, injury, and property-damage-only counts should sum to the total crashes entered. Matching values prevent distorted severity rates and EPDO results.
8. Can I use this for trend comparison?
Yes. Use the same multiplier, crash definitions, and exposure basis across periods or locations. Consistent inputs make year-over-year or site-to-site comparisons more useful.