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Cover image for Real-Time DMS Sign Messages API: What's on the Highway Signs Right Now
Roman Kotenko
Roman Kotenko

Posted on • Originally published at road511.com

Real-Time DMS Sign Messages API: What's on the Highway Signs Right Now

#go #webdev #api #tutorial

Dynamic Message Signs (DMS) — those big electronic boards over highways — display real-time traveler information: incident warnings, travel times, amber alerts, construction notices.

Road511 captures the current message from every DMS sign across 30+ US states and Canadian provinces. Nobody else aggregates this data.

What You Get 

curl "https://api.road511.com/api/v1/features?type=signs&jurisdiction=GA&limit=10" \
  -H "X-API-Key: your_key"
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{
  "data": [
    {
      "id": "ga-sign-i85-042",
      "jurisdiction": "GA",
      "name": "I-85 NB at Clairmont Rd",
      "latitude": 33.8103,
      "longitude": -84.3179,
      "properties": {
        "message": "CRASH AHEAD / I-85 NB AT SR 42 / RIGHT LANE BLOCKED"
      }
    }
  ]
}
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The message field contains the exact text currently displayed on the sign, including line breaks encoded as /.

Why This Matters

DMS messages are a leading indicator. The sign updates within minutes of an incident, often before the event appears in some 511 feeds. Cross-referencing sign messages with traffic events gives you:

  • Faster incident detection — sign changes before event feeds update
  • DOT response time analysis — how long after an incident before a sign is posted
  • Traveler information coverage — which corridors have DMS signs, which are blind spots
  • Historical message patterns — Road511 now tracks message changes over time

Message History

Road511 records every message change in the sign_message_history table. Only actual changes are stored (not every poll), so you get a clean timeline of what each sign displayed and when.

This is data that doesn't exist anywhere else publicly. No state DOT publishes a historical archive of DMS messages.

Use Cases

  • Navigation apps — show upcoming sign messages on the route
  • Traffic management — monitor DMS coverage and response times
  • Research — analyze traveler information effectiveness
  • Emergency alerting — detect amber/silver alerts from sign text

Try It

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