Embedded / law enforcement
Traffic Pursuit Unit
In-car speed measurement and video evidence for police pursuits.
- Main goal
- Produce measurements and video recordings accurate and tamper-evident enough to hold up in court, while keeping every legally approved part inside one separately certifiable unit.
- Business domain
- Embedded / law enforcement
- Size
- Hardware/software product · in police cars · successor to an earlier TPU generation
- Strategic decisions
- Legally relevant functions isolated in an exchangeable MeasuringUnit
- Embedded real-time OS for measuring, Linux for video
- Integer (fixed-point) arithmetic throughout
- Technologies
- C++ · RTOS · ARM
- Keywords
- building-block · runtime-view · quality-scenario · risk · thorough
The Traffic Pursuit Unit (TPU) is a hardware/software system built into police cars. It follows a suspect vehicle, measures its speed profile with high precision, and records video evidence of the violation — accurate enough, and documented well enough, to survive a challenge in court.
Two things make it worth reading as an example. First, it is the only system on this site where the architecture is driven by legal approval: everything a regulatory authority has to certify is deliberately confined to one physically separate MeasuringUnit, so that the rest of the device can be changed without re-certifying it. Second, its authors chose to go deep — the building block view descends to the level of C++ classes and header files, and the runtime view shows the same scenario four times in four different UML notations (sequence, communication, activity, and an extended activity diagram with swim lanes), which is an unusually direct answer to the question of what each notation actually buys you.
Compare the depth here with the other examples on this site: the TPU documentation goes further down than any of them, and its diagrams are hand-drawn in Enterprise Architect rather than generated.