Technology for Transit Systems
Technology for Transit Systems
This domain tests whether you understand what transit technology systems actually do, how their data is produced and validated, and where deployment risk lives. Expect questions on CAD/AVL, automatic passenger counters, transit signal priority, positive train control, GTFS feeds, fare systems, and cybersecurity, usually framed as a deployment or integration scenario.
Core systems
- CAD/AVL provides real-time vehicle location and incident dispatch; it feeds on-time performance and passenger information.
- APC counts boardings and alightings; agencies validate accuracy against manual ride checks before using the data for NTD or load-factor reporting.
- Transit signal priority (TSP) requests extended green or truncated red at signalized intersections; it saves seconds per intersection, and savings multiply across trips.
- Positive train control (PTC) - 49 CFR Part 236 Subpart I - is required on commuter and intercity passenger rail and freight lines, not on light rail or streetcar. CBTC is the moving-block signalling used on many metro systems.
- GTFS is the static schedule/stop feed; GTFS-Realtime is a separate protobuf feed carrying trip updates and vehicle positions. They are not interchangeable.
- Fare systems increasingly use open-loop contactless payment, which shifts risk to reconciliation, back office, and fraud analytics.
Integration and assurance
Technology projects fail on interfaces, not features. Define requirements first, then require factory acceptance testing (FAT), site acceptance testing (SAT), and documented interface control between subsystems. Cybersecurity belongs in the contract: network segmentation, multifactor access, patching obligations, and incident notification.
Worked example
A bus route crosses six signalized intersections. TSP yields an average 15-second saving per intersection. With 30 trips per day: 6 × 15 s × 30 = 2,700 seconds, or 45 vehicle minutes per day. At $120 per vehicle hour, that is roughly $90 per day - but only if the TSP request is actually granted, which is why the evaluation must measure granted versus requested priority, not just the request count.
Traps that cost marks
- Treating GTFS-Realtime as a variation of the static feed, or assuming one vendor supplies both correctly.
- Assuming PTC applies to light rail; it does not.
- Buying technology before requirements and acceptance criteria are written.
- Using raw APC data without validating accuracy against manual counts.
- Leaving cybersecurity, data ownership, and interface responsibility out of the contract.