Road function classes
The Federal Highway Administration classifies every public road by the function it serves in the network, from long-distance mobility to local access. FARS records the class of the road each crash occurred on, and the county, state and year pages here show the share of fatal crashes on each class.
| Class | What it is | US fatal crashes, 2015–2024 |
|---|---|---|
| Interstate | The Interstate Highway System: full access control, no at-grade crossings. | 13% |
| Other freeways and expressways | Non-Interstate roads with full or partial access control and separated directions. | 4% |
| Other principal arterial | Major through routes with at-grade intersections: most numbered US and state highways in and between towns. | 30% |
| Minor arterial | Roads linking towns and connecting to principal arterials, with more access to adjacent land. | 22% |
| Major collector | Roads gathering traffic from local roads and delivering it to arterials; in rural areas, the county road network. | 16% |
| Minor collector | Lower-volume collectors serving smaller communities and land uses. | 3% |
| Local | Every other public road: residential streets, rural lanes, access roads. | 12% |
Shares are of crashes with a reported class. A high interstate share in a county says mainly that an interstate runs through it: interstates carry a large share of travel and have the lowest death rate per mile driven of any class, while the arterial and collector classes, with their intersections, driveways and mixed traffic, account for most deaths.
FARS codes the class from the state's own inventory (FUNC_SYS, from 2015). Crashes on roads not in the state inventory, or with the class not reported, are excluded from the shares.