Montana Crash Explorer
The **Montana Crash Explorer** is a statewide view of 219,480 police-reported crashes from 2016-2025, built on Montana Department of Transportation public data. It runs entirely in the browser: no map server, no query backend, no database behind it. ## Linear referencing, not spatial snapping Crashes are tied to the roads they happened on through MDT's Linear Referencing System - the reference-post and milepost locators carried by both the crash records and the route centerlines - rather than by snapping coordinates to the nearest line. Coordinates are used only to disambiguate divided-highway direction and as a quality check. The result is a line-based representation of crash history, where statistics aggregate onto the route centerline itself. ## A dashboard with no server behind it A Python ETL reduces the master dataset - 219,480 crashes joined to 343,639 vehicle and 454,735 person records - into a small static bundle. The browser fetches a headline summary for first paint, then lazily pulls a single dictionary-encoded fact table and crossfilters it client-side. Filtering the full ten-year record by year, KABCO severity, geography and contributing factors returns in well under a tenth of a second, and the whole site is served as static files from a…