No matter where in the world you're driving, steering wheels are usually built to be closer to the middle of the road rather than the edge. This position gives the driver maximum visibility, thus making for safer travel. But there's a notable exception to this rule: In certain USPS trucks, the driver seat is located on the right of the vehicle instead of the left. This design feature makes parts of a postal worker's job easier, but it also comes with safety concerns.
According to a blog post from CaseyGerry, right-sided steering wheels offer numerous advantages for mail delivery workers. In rural areas, drivers are able to deposit parcels into mailboxes without leaving their seats, saving them time and effort.
It's also better for the vehicle. Postal workers are legally required to turn off the engine and take their keys with them every time they get out. All that starting and stopping can wear out the equipment over time and shorten the truck's lifespan.
Even in cities where mail needs to be delivered at the door, sitting on the right side of the vehicle is practical. Instead of potentially opening their door and stepping into traffic, postal workers can go directly from their seat to the sidewalk.
Reversing the standard layout for USPS trucks wasn't a decision the government made lightly. Even if they're limited to mail routes, trucks with right-sided steering wheels can be dangerous. They give the driver a poorer view of on-coming traffic than they would get if they were positioned closer to the center of the road. For this reason, postal workers aren't allowed to make U-turns or left-turns while driving mail delivery trucks. They're also required to complete approximately 12 hours of classroom and behind-the-wheel training before they're allowed to drive on the job.
Government postal workers aren't the only delivery people banned from turning left. UPS drivers are required to follow this same rule, but the reason has just as much to do with efficiency as it does with safety.