I don't know where you're from, but around here highway dollars are spent expanding and rebuilding highways to increase capacity and throughput. Projects that focus on only safety -- removing left-lane exits and entrances, adding full-width paved shoulders, increasing grade, increasing curve radius, etc -- are rare-to-non-existant uses of scarce highway dollars.

States -- especially California -- have a serious interest in increased highway efficiency. The only thing about the original premise that I wonder is how much additional wear-and-tear the high speed lane would create, especially considering it would need to be kept in optimal condition to avoid deleterious safety affects at such high speeds.

Not much - wear and tear is strongly a function of vehicle weight, a lane with no big rigs doesn't suffer much.

And with enforced control over the vehicles you could make the lane narrower and even have a low kerb to stop people cutting in and out.

Popular in europe are guided bus ways. you put a low concrete kerb in a very narrow lane ie. 12 inches wider than the bus. There are small guide wheels that run against the kerb and servo the steering. So you can run a two way full size bus route in almost the same width as a single rail line - and at the end of the route it can pull out into normal traffic. This is just a software alternative.

They do have an incentive to avoid 4hour queues in people getting to work - at least when those queues mean companies start moving to other cities because of the traffic.

That's why cities are forever building new freeways, widening freeways, building bridges etc.

The cities don't get blamed for pileups in the same way that airports don't get blamed for plane crashes.

what is the incentive for highway planners? Isn't how many companies are in the area a little indirect of an incentive? How does it impact their individual wellbeing?

An indirect political incentive is a very weak incentive. There is more direct incentive to do nothing innovative.