Introduction
Computer Aided Dispatch (CAD) and Automated Vehicle Location (AVL) systems are the operational nerve center of most transit agencies. CAD supports dispatchers with communication, incident management, and service adjustments. AVL tracks vehicle location, speed, and heading in near real time.
Together, CAD/AVL generates the operational data that powers control centers, passenger information, and performance analytics — often alongside or upstream of GTFS-Realtime feeds.
What CAD/AVL systems do
Dispatch and communication
CAD systems enable two-way radio or data communication between dispatchers and operators. They log incidents, support run cutting, manage detours, and provide operators with schedule and route information.
Vehicle location and tracking
AVL uses GPS (and sometimes other sensors) to report vehicle position at regular intervals — typically every 5 to 30 seconds. This data feeds live maps, arrival prediction systems, and historical operational archives.
Event logging
CAD/AVL records operational events that analytics depend on:
- Arrivals and departures at stops
- Route and block assignments
- Odometer and heading data
- Operator login and trip start/end times
- Incidents, delays, and service exceptions
CAD/AVL vs. GTFS-Realtime
These systems are related but not identical:
| CAD/AVL | GTFS-Realtime | |
|---|---|---|
| Primary users | Dispatch, operations | Passenger info, third-party apps |
| Data format | Vendor-specific, often proprietary | Standardized protobuf/JSON feeds |
| Granularity | Dispatch-grade events | Trip updates, vehicle positions, alerts |
| Typical role | Source system | Published consumer feed |
Many agencies publish GTFS-RT derived from CAD/AVL. Analytics platforms may ingest either or both, depending on data availability and quality.
How CAD/AVL supports analytics
Operational feeds from CAD/AVL enable:
- Live fleet monitoring — vehicle progression, off-route detection, gap identification
- On-time performance — actual vs. scheduled times at timepoints
- Running time analysis — segment travel times compared to schedule
- Service reliability — operated vs. scheduled trips, missed trip detection
- Historical trending — performance before and after schedule or network changes
When combined with GTFS (scheduled baseline) and APC (passenger counts), CAD/AVL completes the picture of what ran, when, and with how many passengers.
Integration challenges
CAD/AVL data is rich but not always analytics-ready:
- Stop and trip ID mapping must align with GTFS identifiers
- Vendor formats vary — integration often requires custom connectors or export pipelines
- Data latency differs from published GTFS-RT feeds
- Archive completeness — historical retention policies affect long-term trend analysis
Agencies should treat CAD/AVL integration as a data governance priority, with documented ID mappings and feed health monitoring.
Using existing on-board infrastructure
A key advantage for many agencies is that CAD/AVL already exists on every revenue vehicle. Bus RT Insights leverages this existing on-board infrastructure — no additional hardware installation — connecting operational feeds with GTFS, GTFS-RT, and ridership data in a unified analytics environment.
Conclusion
CAD/AVL is the primary source of truth for what vehicles actually did on the street. Understanding how it works — and how it connects to GTFS and analytics platforms — is essential for operational visibility and performance management.
Learn more about platform data integration or contact us for a demonstration.