[m-j-fox]

Here's my idea: Rather than high-occupancy lets make the left lane a guaranteed-speed lane. The rule is that all cars in the lane move at 80 mph. If you can't merge in or out of the lane is such a way that no one else has to brake, then you're not allowed to merge. You're not allowed to slow down unless there's an emergency and those will be rare because users will be required to maintain their vehicles in top condition and crashing is strictly prohibited.

This will dramatically increase the throughput of the lane and will inescapably lead to an increase in usage. But the increase will naturally be capped around 20k cars per hour per lane.

To make it work, you'll need precise data about conditions far ahead and far behind. You'll also need an inescapable enforcement mechanism or the system will succumb to cheating. The good news is that very soon many cars will be covered in sensors, networked and able to implement the concept.

[secabeen]

How do cars exit the guaranteed-speed lane if the left-most normal lane is only going at 25mph?

[dragonwriter]

I don't actually think the concept is a good one (it's unworkable without a level of automation at which you'd have much better alternatives) but the exit problem is already frequently addressed with HOV/bus lanes—have dedicated left-sode exits so they don't need to cross the slower lanes to exit.

[m-j-fox]

I agree advanced automation would be needed to maximize capacity. A basic system only needs cruise control, lights and cameras installed at the merge points and a transponder like fasttrak that monitors your speed and automatically fines you if you hit the brakes. Adaptive cruise control, lane assist, higher standards of maintenance and driver skill don't seem like too much to ask of a select group of people and vehicles licenced to use the lane and would help to maximize capacity and minimize incidents without getting too futuristic.