RTG vs RMG: telling yard cranes apart from above

The tell is in the rails, not the crane

When you're working a terminal from overhead imagery instead of walking the yard, you read the ground, not just the machine. A rubber tyred gantry runs on tires, free to steer in and out of a block, turn, and shift to the next row. A rail mounted gantry is locked to a fixed pair of rails for the full length of a block, with no lateral movement at all. From directly above, the RTG shows no rail lines beneath it, maybe a paved travel lane or tire scuff, while the RMG sits on two long parallel rails running the length of the stacking block, usually visible as two thin straight lines flanking the crane's wheels.

That's the fastest check. Rails present, call it RMG. No rails, call it RTG.

Span, stance, and shadow

Once the rail question is answered, look at stance. RTGs tend to run narrower, typically six to seven container rows wide plus a travel lane, and their legs flare outward at an angle, giving the machine an A-frame look in plan view. RMGs often span wider, sometimes stacking blocks over ten rows or more, and their legs sit closer to vertical, straight down to the rail, so the footprint reads as a tighter rectangle.

Shadow length at midday gives you a rough height check if you need one. RTGs generally run lower than RMGs of the same generation, though newer high-stack RTGs are closing that gap. Don't lean on height alone to separate the two types.

Tire marks matter too. On an RTG row you'll often see curved tread patterns in the paving where the crane has steered end to end, especially near block ends where it turns to change rows. An RMG block shows none of that, just the rail and ballast or a paved strip between the rails, dead straight.

Where this gets confusing

Some terminals run rail mounted cranes with rails flush to the pavement, hard to pick out at coarser resolution. This is where image quality starts to matter. Drop the ground sample distance too low and you can lose the rail line entirely, mistaking an RMG for an RTG, which throws off a count if you're tallying crane types across a market.

Automated stacking cranes add another wrinkle. They're rail mounted by definition but often paired in twin configurations over a block, one crane working the seaside and another the landside. From directly above, twin ASCs can read as a single wide crane unless you can resolve the gap between the two machines.

Ship-to-shore cranes aren't part of this comparison at all. STS cranes sit on rails too, but they run perpendicular to the berth, not parallel to stacking blocks, and the boom and backreach make them unmistakable regardless of what's underneath.

Why it's worth getting right

Misreading RTG for RMG, or missing an ASC pair, skews your count of what yard equipment a terminal is actually running, and that undermines any read on which manufacturers are winning share in gantry cranes versus the older tired fleets they're replacing. Getting the rail question right block by block is the difference between a usable dataset and a rough guess.

Crane Fleet Mapping builds that terminal-by-terminal crane inventory every year, reading yard crane type and rough dimensions off satellite and aerial imagery so you're not sending a team to every port to find out what's stacking containers there.

If your crane count needs that kind of resolution, Crane Fleet Mapping is worth a look.