It's people that have the highest impact milage. We can pack food tightly into a truck and they don't mind waiting when the packing takes some time.
We can't easily pack humans more densely into trucks, so reducing their miles traveled has a much bigger effect (and if the distances are shorter they can also walk/bike/bus instead of single occupancy vehicle).
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.
Well, as this article is about the Netherlands, you can go and have a look there, at rush hour. Say, boarding a train from Almere to Amsterdam. And the answer is: a lot..
Regardless, the relative price of food is usually a reasonable proxy for the amount of energy that went into its production. If the food from the urban farm is more expensive than equivalent food from an industrial farm, it probably took more energy to produce (and consequently probably released more greenhouse gases during its production).
I find your message confusing, when you say price, do you talk about final retail price or production cost? (fruits and vegetable are high margin products in food distribution)
When you talk about energy, do you take into account human labour? Natural ressources are considered free in our current economic system, that is why it is cheaper to grow food by damaging the amazonian forest with nasty coal/oil fed machine rather than doing local permaculture with more human beings and passive tools.
We can't easily pack humans more densely into trucks, so reducing their miles traveled has a much bigger effect (and if the distances are shorter they can also walk/bike/bus instead of single occupancy vehicle).