Most of that material has been moved in Australia too, with the lion's share of Caterpillar's autonomous haulers operating in the Western Australian Pilbara.

At one stage virtually all of the Caterpillar autonomous trucks were hauling iron ore - and indeed much of the initial information the OEM was touting about the performance benefits was gleaned from their service with Fortescue Metals Group.

Indeed, when Caterpillar announced its autonomous trucks had moved 1 billion tonnes in November 2018, it followed up with a press release about 1Bt being moved at FMG by autonomous trucks.

Caterpillar passed the 2Bt milestone in April 2020 and moved another 1Bt in little more than one year.

Not bad considering the first six-strong fleet of this iteration of Caterpillar's autonomous trucks in rolled out in 2013 with FMG.

Caterpillar Resource Industries vice-president Marc Cameron said the time between the major milestone targets was decreasing because the implementation efficiency from initial contract to full deployment was becoming more efficient.

"Consistent with previous milestone trends we anticipate crossing the 4Bt threshold at even a faster pace than achieving 3Bt," he said.

"Looking forward, we are planning the expansion of Command for hauling to including our 140t class Cat 785 mining truck."

While iron ore in the Pilbara was the main game for a while, these days there are fleets of trucks operating across North America, South America and Australia hauling, besides iron ore, oil sands, copper, coal and gold.

This was not Big Yellow's first attempt at autonomous haulage. It created an autonomous hauler in the late 1980s and unveiled it with great fanfare to an unsuspecting mining audience. Sadly, the "build it and t[he]y will come" catchcry of a film released around that time did not apply to miners in the 1980s and the truck was parked up.

Then Komatsu stole a march when it started to get autonomous trucks into mines in Chile and Australia in the early 2000s.

At Minexpo 2008 Caterpillar was touting its own autonomous project which was based around a Chevy Suburban.

However, when it finally pressed the button on its own autonomous haulers it used a clever gambit - it made its Minestar Command for hauling system retrofittable to existing trucks, particularly its 793F 220t haul trucks which were introduced around 2008.

Those 793Fs came prepared to have the Command for hauling system plugged in.

At the time Komatsu was insisting anyone who wanted its autonomous haulage system had to buy brand new trucks with all the equipment for autonomous haulage fitted.

That made Caterpillar's autonomous haulage system more attractive because it could be fitted to existing trucks meaning a lower cost of entry.

These days Command for hauling has been applied to class sizes ranging from 190t to 360ts including the 789D, 793D, 793F, 797F and the 297t electric drive 794AC.

Command retrofit kits are available for Caterpillar and other brands of trucks and loading equipment. Caterpillar has successfully applied the technology to a Komatsu haul truck.

Caterpillar Minestar Solutions director Jim Hawkins said since surpassing the 2Bt milestone the OEM had equipped more mines with Command trucks and established the world's first gold mining application for Command for hauling.

"Since surpassing 1Bt we've expanded our Command fleet by nearly 250%."

That gold mining operation Hawkins refers to is also in WA.

Since the first AHS trucks were commissioned in 2013 the Command for hauling fleet has collectively travelled more than 110 million kilometres - equivalent to a minimum-distance straight-line journey to Mars - with no lost time injuries associated with automated truck operation.

Customers have reported up to 30% greater productivity.