Elsewhere, someone here linked to the national crash data set. Sounds like they used PostgreSQL/Postgis for the backend here to store the data. The web server grabbed it as GeoJSON and displayed with a mapping web framework like Leaflet.
I did a crash analysis locally using the QGIS desktop software for some display and analysis, as well as Node.js and the Turf.js library when custom code was needed for spatial analsyis:
