CommuteScout Bulk Snapshots
Gzipped JSON snapshots of the same records as the map markers (live.json.gz rebuilt every 30 seconds with incidents, closures, chain controls, wildfires and toll prices; signs.json.gz every 5 minutes with message signs and road weather; cameras.json.gz), served from data.commutescout.com. The developers page says their shape follows the map, not the API, and can change between releases; no schema is published.