That might make sense for dump trucks because they're bulky and have poor visibility, but what's the increased risk of passing on the right? The only thing I can think of is marginally worse visibility because the right side is slightly further away from the driver's seat. However, I don't think that's enough risk to justify going out of your way to pass on the right. Having to change lanes to pass on the left carries its own risks.

Some cars have a blind spot on their right. Also, the convention is passing on the left, so people are generally less aware of things going on on their right. Of course bad drivers are almost by definition unpredictable, but if some bad driver is going to absent mindedly merge into you, they will probably do it while you are on their right. In particular, distracted people whose texting has been interrupted by their GPS telling them to take the next exit...

In many countries, it's a hard rule that you need to pass on the left. Passing on the right is only allowed when it's a lane going in a different direction (like an exit), or traffic is moving very slowly (you don't want people changing lanes in a traffic jam to avoid passing on the right).

While "keep right except to pass" is technically the law here in Ontario, the de facto standard is that the middle lane is the cruising lane, the left is the passing lane, and the right is basically a second merging lane. This means that it is not uncommon to have stop-and-go traffic in the left two lanes while the right lane is still moving and mostly wide open. Drivers will frequently move right into the middle lane from the ramp even with no traffic in the right lane and not having sped up to the highway speed. It's an complete waste of resources.

Highways are a complicated graph problem I guess, which I'm not very good at, but I wouldn't be surprised if the true bottleneck was some offramp later. So, increasing the throughput of the road leading up to it shouldn't really improve things, right? And leaving rightmost lane less heavily populated might make it easier for cars to do the off/on ramp thing which might make things easier around the bottleneck.

I dunno. People pack in as tightly as possible around here and we still get traffic. I think it is just inevitable.

Going onto the IdiotsInCars subreddit, it's kind of shocking how commonplace it is for people to undertake other road users by speeding past in the slow lane. It's already more difficult to merge back into a slower lane because you have a much bigger blind-spot (and have to twist your neck a lot more to get a good look), so it doesn't make it any easier if you have to expect that people will be speeding to undertake you.

I hate it when my GPS on my second phone does this!

On a serious note, the overtake left thing (or right for those strange people driving on the wrong side) is a big reason German Autobahn is as safe as it is. Reckless idiots notwithstanding.

On a 3+ lane road, it increases the risk of two people merging into each other as they both try to pass.

Unfortunately the majority of people don't seem to understand they're not allowed to pass on the right (and they never get pulled over for it).

If slower traffic kept right, there’d be a lot less passing on the right. (If you’re getting passed on the right regularly, you might consider your own lane discipline as well as that of those passing you.)

Yes, this is also true, but I think the bigger problem is just speeding. People on the left are usually moving faster than people on the right or middle, on average, but some people want to go 20-30 mph over the speed limit. Normally I'd pull to the right so they can pass, but by the time I start doing that they're already starting to change lanes too!

True. If you take a highway that people feel is reasonable and prudent to drive at 75-85 mph and post it as 55, people will drive 20-30 mph over. I think the problem is more likely the 55 signage in that case.