Exxon trucks have had this arrangement on the trailer for years. I always thought the doolie arrangement was for weight distribution, not safety (though 2 is safer than 1). The tires on the Exxon trailers cannot be retreaded, from what I've read, but also last a little longer than the older, smaller ones. No retreads = safer, I would think? Dunno. Apparently (from the link) they CAN be retreaded.