What to ask a vendor about GPS reporting

Reporting interval is a means, not an end

A GPS reporting interval is not a quality score. It is a constraint that determines which features are possible. Understanding which features you actually need is the way to evaluate whether a given interval is adequate for your routes.

The figures below are general engineering arithmetic rather than any particular vendor's specification — including ours. Use them to interrogate a quote, not to assume one.

Here is roughly what each band supports.

60 seconds

Adequate for answering "where is the vehicle now" at coarse resolution. At 40 km/h a vehicle covers about 660 metres between reports, which in an urban area can span several turns. The map trace becomes a series of straight lines between points that ignore the actual road taken.

This is enough for basic fleet visibility. It is not enough for geofence accuracy: a stop geofence of 100 metres radius can be entered and exited entirely between two reports, producing no arrival event at all.

30 seconds

Around 330 metres between reports at 40 km/h. Geofence detection becomes mostly reliable for larger fences, and the map trace begins to resemble the road. Arrival-time accuracy is around ±15 seconds, which is fine for reporting and marginal for a parent proximity alert.

10 seconds

Around 110 metres between reports at 40 km/h, and about 30 metres in slow traffic. This is the band where a few things become properly reliable rather than mostly reliable:

• Geofence events fire consistently even for tight stop fences, because a vehicle cannot traverse a 100-metre fence between reports at any realistic school-route speed.
• Proximity alerts become useful. A parent asking for five minutes' warning gets a notification with an error measured in seconds, which is the difference between a useful alert and one people learn to ignore.
• The trace follows the road. Trip replay shows the route actually taken, which matters when a deviation is being investigated.
• Stop dwell time is measurable. How long the vehicle waited at each stop becomes a number rather than an estimate.

1–5 seconds

Better resolution, considerably more cellular data, and battery implications on units that are not hard-wired. The marginal operational value for a school route is small once you already have reliable geofencing and second-accurate arrival times. The genuine use cases are accident reconstruction and detailed driving-behaviour analysis.

The thing that matters more than interval

Speed and harsh-driving detection should not depend on the reporting interval at all, and if a vendor implies it does, that tells you something about their architecture.

Consider speed violation detection with server-side evaluation at a 30-second interval. The vehicle accelerates to 20 km/h over the limit for 15 seconds and slows back down. Both surrounding reports show a legal speed. The violation is invisible.

The correct design evaluates thresholds on the device, continuously, using the GPS receiver's own sampling rate — which is typically 1 Hz regardless of how often the unit transmits. The violation is detected locally, recorded with its peak, duration and location, and transmitted as an event. The reporting interval affects when you hear about it, not whether it was caught.

The same applies to harsh acceleration and harsh braking, which are derivatives and therefore completely invisible at any practical transmission interval.

So the question to ask a vendor is not "how often does it report" but "where is the threshold evaluated". If the answer is the server, their speed data is a sample of a sample.

Coverage gaps, and what happens to your data

The second question worth asking: what happens on the stretch of your route with no signal.

There are two possible answers.

Events are buffered on the device and flushed on reconnect. The live map goes stale for the duration of the gap, and then the history fills in completely. Trip replay afterwards is intact. Attendance for that trip is complete.

Events are dropped. The live map goes stale and the history has a hole in it permanently. The trip that went through the gap cannot be replayed, and any boarding that happened there is lost.

For a school route this is not a subtle distinction. Rural and semi-urban routes routinely have gaps, and a hole in the attendance record is precisely the hole that will matter.

The four questions worth asking

1. What is the reporting interval during an active trip, and does it change outside trip hours?
2. Where are speed and harsh-driving thresholds evaluated — on the device or on the server?
3. What happens to events during a coverage gap — are they buffered and delivered later, or lost?
4. Is a unit that stops reporting raised as a fault, or does it simply disappear from the map?

Those four together determine whether the tracking data can be relied on. The interval alone does not, and a vendor who answers only the first question has told you the least useful part.

Worth noting on question one: newer 4G-enabled devices sit in a different place on the data-cost curve than older 2G and GPRS hardware, so an interval that was expensive to sustain a few years ago may not be now. Ask what the device actually is, not just how often it reports.