[dredmorbius]

Maximum tractor-trailer weight in the US is 80,000 lb, with typical weight closer to 44,000 lb. Dry weight is about 32,000 lb, for a maximum payload of 48,000 lb.

An articulated bus has a curb weight of about 35,000 lb and a capacity of up to 92 passengers. At 177 lb each, that's a gross weight of 51,284 lb. (net: 16,284 lb of passengers).

I'd presume a potato's density is close to that of water. As such, capacity is actually mass rather than volume-constrained --- you'd be unable to fill a truck to its volumetric carrying capacity before exceeding gross vehicle weight limits.

Many grocery products have much lower density: chips, bread, paper products, etc.

I still tend to agree it makes more sense to move goods than people, but the differential may not be quite as great as you might think.