The problem
An oversize load is not allowed to take the fast way. Every state issues its own single-trip permit, and each one prescribes an exact authorized route — this ramp, that bridge, these miles. Leaving it is a violation, and on a 68-foot shed at 13’6” it can also be a struck overpass.
Every consumer navigation app does the one thing this driver must never accept: it re-routes. Traffic, a closure, a faster line — it silently moves you onto a road nobody permitted. Meanwhile the permits themselves arrive as scanned images with no text layer, one per state, so a single haul from Ohio to Pennsylvania is two documents that have to be recognised as one move.
The approach
The permit is the source of truth, and the app is built so that nothing can quietly become the authority instead.
Permits arrive by email or bulk upload and are read by a vision model that is told to transcribe, never reconstruct — no inferring a connecting road, no filling a gap, and coordinates are forbidden outright, because a plausible position for “SR 0022 at the WV line” is a confident wrong answer nothing downstream can detect. Placing those road names on the earth is a separate, checkable step: geocode, snap to roads, then refuse to draw unless the result clears three guards — the match must be a place rather than a county centroid and in the right state, no point may sit off the corridor its neighbours describe, and the finished line must be about as long as the permit says the move is. That last one is the strongest, because the paper prints its own mileage, so a line of the wrong length is provably not that route.
Connected permits stitch into one trip on the hand-off each document declares, corroborated by the calendar — legs of one haul are days apart, not seasons. Where a state’s permit is missing, the gap is named rather than hidden.
The line on the map is always labelled as an approximation, and a route the app worked out never arms the off-route alarm. Stopping a driver for the app’s own geocoding error teaches him the alarm is noise, and the next one fires on a route read off the paper.
The result
A driver navigates the permitted route and nothing else: live GPS projected onto the authorized line, maneuvers and restrictions pinned to distance along it, and an alarm — never a re-route — when the truck leaves it. Around that sits the rest of the operation: an email ingest pipeline that classifies arriving documents and bounces junk with a reply, a company console where a carrier distributes permits to drivers, a platform admin console, community road tags with satellite views of the parking, and a CI pipeline that builds and ships to testers in eight minutes.
The engineering discipline the product demanded turned out to be the interesting part: at every step where the software could have guessed, it either proves the guess against something the paper already says, or declines and shows the driver the route table instead.