There may have also been height issues with the enclosed trailers. The open ones are more adjustable. I know one of the enclosed BMW trailers hit an overpass right near my house, and totaled about 6 or seven new cars in an instant.

Also, I would gather a regular tractor is a whole lot more comfortable for the driver, and much more fuel efficient, than those Cab-over trucks they were using.

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2014 BMW 328i Xdrive
2011 BMW 335i M-Sport
2008 BMW X5 4.8i Sport
2000 BMW 528i 5sp