Geofences and Their Disputes
A geofence is a circle on a map. When a vehicle crosses it, a system records an event, and that event frequently becomes the start of a billable interval. For a software-oriented reference on recording work time, this discussion.
Which means a radius somebody chose, usually without documenting why, decides whether a charge exists. That is a weaker foundation than most people assume, and it produces a recognisable set of disputes. For broader transportation and measurement context, see DOT Office of Inspector General.
Six ways they go wrong
Too tight. A 100-metre radius around a building misses a driver queueing on the access road, and the queue is often the longest segment. The carrier's system says arrival at 15:40; the driver was in line from 14:10.
Too loose. A 1-kilometre radius catches the truck stop across the highway, a fuel stop, and the driver's lunch. Now arrival is recorded before arrival, and the facility will say so.
Centred wrongly. On the office rather than the gate, on the postal address rather than the entrance, or on a pin somebody dropped approximately.
GPS drift. Urban canyons, warehouse interiors, weather. A vehicle stationary at a dock can appear to exit and re-enter, generating multiple arrival events and an interval nobody can reconstruct.
Adjacent facilities. Industrial parks where three receivers share an access road. One geofence, three destinations, and events attributed to whichever was configured.
And the trailer versus the tractor. A tracker on the trailer records a different visit from one on the tractor, and after a drop-and-hook they diverge permanently.
What a specified geofence looks like
If a geofence is going to determine money, it needs describing the way any other measuring instrument would.
Centre point, stated as coordinates, not as an address.
Radius, stated in metres, with the reason. 300m, chosen to include the access road queue.
Which vehicle it tracks — tractor or trailer.
Dwell threshold before an event counts. Requiring the vehicle to remain inside for, say, three minutes eliminates most drift and pass-through noise.
And a re-entry rule. If the vehicle exits and re-enters within some window, treat it as one visit. Otherwise drift creates two.
Five lines. Put them in the rate confirmation alongside the start and stop events, and the instrument becomes describable rather than assumed.
Why they are still worth using
Despite all of the above.
They are automatic. No driver action, so no forgetting, no dispute about whether a message was sent.
They are independent of duty status. Unlike an ELD's on-duty declaration, a geofence event is derived from position, so a driver who logs off duty during a wait has not destroyed the arrival record.
And they work without the facility's cooperation, which matters when there is no gate data to be had.
A specified geofence plus one other source is a strong evidentiary position. An unspecified one is an assertion with coordinates.
The comparison that resolves most arguments
Geofence entry against facility gate-in.
They should differ by a small, consistent amount — the time from crossing the radius to reaching the gate. If the gap is stable, both instruments are working and you can convert between them.
If the gap is erratic, one of them is wrong, and the pattern says which. Erratic in one direction suggests a queue outside the fence; erratic in both suggests drift or a badly placed centre.
Running that comparison for a fortnight at a regular facility is the cheapest calibration available, and it converts a contested number into an agreed one.
What not to do
Do not resize the fence during a dispute. It looks exactly like what it looks like, and it destroys the credibility of the historical data too.
Do not use different radii for different customers without saying so.
And do not treat a geofence event as arrival in the contract. Say geofence entry as specified in Appendix A, because arrival is an interpretation and a geofence event is a record.
The short version
- A radius somebody chose, usually undocumented, decides whether a billable interval started
- Six failure modes: too tight, too loose, badly centred, GPS drift, adjacent facilities, and tractor versus trailer
- Specify it like an instrument: coordinates, radius with a reason, which vehicle, a dwell threshold, and a re-entry rule
- They remain valuable because they are automatic, independent of duty status, and work without facility cooperation
- Compare geofence entry against gate-in for a fortnight; a stable gap means both work, an erratic one says which is broken
- Never resize the fence during a dispute, and never write "arrival" where you mean a specified event