Here's a good thing for vehicle designers to keep in mind: If it operates in traffic, it will have to fit inside a rectangular cross section.
A rectangular cross section maximizes the carrier's volume capacity. Any element that projects beyond the square boundary, such as mirrors, exhaust pipes or antennas, must be absolutely necessary, because it's prone to being broken off.
Lane width and bridge height restrictions define the boundaries of the rectangle. Sometimes vehicle length constraints can affect vehicle shapes, especially for low speed designs where streamlining doesn't matter.
The cab-over-engine design that was popular from the 1950s to the 1970s was a response to length restrictions. When those restrictions were relaxed and trucks could be made longer, cabovers became more unusual.
This principle applies not only to road vehicles, but also to rail traffic and to shipping, especially when it must traverse narrow sea lanes and canals.