A heavy truck uses more gas than a light one. It's never free to move heavy things around, it's just another externality. There's certainly some economy of scal

A heavy truck uses more gas than a light one. It's never free to move heavy things around, it's just another externality. There's certainly some economy of scale to having the grocery store do the moving instead of individually owned cars doing 'small' (on an industrial scale) runs to depots, but it's really pretty hard to account for.