What Caltrans changeable message signs are displaying right now.

Data: statewide CMS sign text, blank and out-of-service signs already
filtered - every record is a message a driver is physically seeing.
Signs carry the road's operational truth ("CHAINS REQUIRED 10 MI
AHEAD", "FULL CLOSURE HWY 96 DUE TO FIRE", "PREPARE TO STOP"), often
before the event shows up in any other feed. Refresh: ~2-minute cache.

Filters: route (e.g. "I-80") and/or center "lat,lon" with radius_km.
Quote sign text verbatim to the user - it is the most current and
most local signal this server has.