Why let the device check in?
A manual call-in depends on signal, a phone and a driver who remembers. A geofence event arrives by itself, with the time and the position. People then deal only with the exceptions: a point not reached, a stop that is too long, a stop where none was planned.
How big must a call-in geofence be?
A vehicle that drives through a circle without stopping must leave at least one position inside it. Through the centre it covers 2 x r of road, so the radius must cover half the distance driven between two positions, plus the position error.
When is a vehicle expected at each point?
Expected time adds the driving time of each leg to the departure time, plus the planned stops before the point. The overdue alarm waits a grace period: a fixed number of minutes, or a share of the leg, whichever is larger.
| Point | Radius | Event | Expected | Overdue alarm |
|---|---|---|---|---|
| Base gate | 200 m | Exit | 05:30 | No alarm |
| Call-in 1, km 120 | 350 m | Enter | 07:13 | 07:43 |
| Rest area, 30 min | 200 m | Enter and exit | 09:04 | 09:34 |
| Call-in 2, km 380 | 350 m | Enter | 11:26 | 11:56 |
| Site gate, km 470 | 200 m | Enter | 12:43 | 13:13 |
Which alarms does the sheet set?
- Overdue: the vehicle has not entered the next geofence by the overdue time.
- Escalation: still no event after the further minutes, so the next person is called.
- Long rest: the vehicle stays in a rest geofence longer than the stop plus the tolerance.
- Unplanned stop: the vehicle is stopped outside every geofence for too long.
Assumptions and limits
- This designer does not write or approve a journey plan. It starts from points your team already approved.
- Road km and an average speed give expected times, not a forecast of traffic or weather.
- Interval, accuracy and radii are typical values, not Tracom specifications. The 4000 geofence slots are the published Tracom ST100 value.
- Whether the overdue logic runs on the device or on the platform depends on your device model and platform. Ask before you rely on it.
- The calculations run in your browser. Your inputs reach our server only if you ask for the emailed report, and are then kept for up to 45 days.
Sources
- IOGP Report 365-19: Land transportation safety recommended practice, journey management
- GPS.gov: GPS accuracy
Sources and date checked: 3 November 2026. The radius rule is plain geometry. The 4000 geofences are the published Tracom ST100 value. Verify alarm times against your own HSE procedure.