GPS and the tech behind real-time shipment tracking

For all the progress made elsewhere in supply chains, the middle mile is still a blind spot for many shippers. A shipment leaves one site and effectively disappears until it turns up at the next, with no way to see a delay coming or plan around it. The freight providers closing that gap are doing it with GPS tracking, turning a shipment’s position into something visible throughout the journey, updated as it moves, rather than something a shipper finds out after the fact.

In this article, we’ll look at how GPS tracking actually works, what real-time really means in practice, and what to look for from a provider.

GPS, or Global Positioning System, works by using signals from a network of orbiting satellites. A GPS receiver fitted to a vehicle picks up signals from several satellites at once and calculates its own position from the small differences in when each signal arrives. The more satellites in range, the more precise that position. The receiver repeats this calculation at set intervals, which is what allows a vehicle’s location to be tracked as it moves.

Once a vehicle’s GPS position is live, that data can be used to automate records at specific locations. This is where geofencing comes in. Geofencing is a virtual boundary drawn around a physical location, such as a collection site or delivery dock. When a GPS-tracked vehicle crosses that boundary, it automatically logs an arrival or departure, without anyone needing to record it manually.

That automation is what produces accurate dwell time (how long a vehicle actually spends at a site) rather than an estimate based on a paper log or someone remembering to note the time down. Once arrival and departure data is consistent, it feeds directly into on-time-in-full (OTIF) reporting and detention tracking, making patterns visible across a shipper’s whole freight volume rather than relying on records that vary from site to site.

GPS coordinates are the most sophisticated way to track your shipment in real-time. Other methods, like a driver phoning in a location or a status update generated when a shipment was last scanned at a depot, can tell you where a load was at some past moment, but not where it is live.

That distinction is why it’s worth asking a freight provider specifically whether their tracking is GPS-based. A phone check-in every few hours can look similar to real-time tracking on paper, but the difference will show up during a delay, when knowing the current position allows a shipper to act confidently and quickly.

Capturing a vehicle’s position is only the first step. That data has to reach a shipper’s screen, and combined with other information to produce an estimated time of arrival.

Once a device captures a position, it needs to get that data off the vehicle and into a system a shipper can see. This usually happens over a cellular network, with satellite connections as a backup on routes where cellular coverage drops out. From there, the data is sent to a platform that ingests it and normalises it, converting raw signals from different devices and formats into a single, consistent view.

Coverage gaps are inevitable on some routes, so systems typically handle this through buffering and store-and-forward. The device holds onto position data locally when it can’t transmit, then sends the backlog once a connection is available again, rather than losing that stretch of the journey entirely.

From there, the data reaches a shipper through integration routes like API feeds, connecting directly into a transport management system (TMS) or customer-facing portal.

A basic ETA can be calculated by simply dividing the remaining distance by an assumed speed. This ignores almost everything that actually affects a journey, like traffic, weather, how long a vehicle tends to dwell at a particular site, or how a specific lane has historically performed.

Machine learning models improve on this process by learning from that data. The result is a prediction that adjusts as conditions change, rather than a fixed estimate calculated once at departure.

“Real-time” sounds like a single, precise standard, but it covers a range of different update frequencies and technologies.

Real-time usually means the position updates at regular, frequent intervals. Typical intervals might range from every few minutes to closer to real time for high-priority loads. That frequency is a deliberate trade-off: more frequent updates use more battery and data, so providers balance update frequency against those costs.

For most freight, an update every few minutes is more than enough to track progress and catch a delay early. Higher-value or time-critical loads can justify more frequent updates, since the cost of missing a problem is higher than the cost of the extra data.

Two separate things affect how much you can trust an ETA: position accuracy (how precisely the system knows where the vehicle is) and data freshness (how recently that position was updated). A highly accurate position that’s an hour old is just as unhelpful as a fresh update with a wide margin of error. Both leave a gap between what you’re seeing and what’s actually happening.

Before relying on a provider’s tracking, it’s worth asking for more details about their tracking service. Amazon Freight, for example, offers GPS-based real-time freight tracking through its online portal, backed by 24/7 support, so shippers have a direct way to check a shipment’s status, live.

See how Amazon Freight can help you achieve more visibility and control over your shipments. Create a free shipper account today.