But that's an enormous inversion of expense that falls on the trailer owners. The tractor-trailer model works so well because it concentrates complexity and cost in the tractor.

At present trailers are mechanically fairly simple and require only routine servicing with a basic toolkit. They draw power from their tractor. An owner can maintain a fleet of trailers to match their peak demand and are immediately available. Just charter a tractor and away they go.

Battery-equipped trailers will be much more complex, heavy and maintenance-intensive. More expensive but with a smaller payload and prolonged periods of unavailability whilst charging. The cost of haulage charters will have to reduce by magnitudes to make that an attractive preposition.