Other studies (one in New Jersey, I believe) have shown this as well. HOV lanes increase traffic congestion. This carpool lane thing was always more about social engineering than it was about improving traffic flow.

This is also no shocker:

A report released last year also shows that the most common form of HOV lane, where general and restricted traffic is not separated by a physical barrier, causes a fifty percent increase in accidents.

Car pool lanes with no barriers are nuts, and single-lane carpool lanes are pointless, because one slowpoke can hold up everyone behind. Get rid of them all. Now.

I love the "solution" that the guy here in Denver used, until he got busted for it. He put a mannequin in the passenger seat so he could use the HOV lane.

After getting busted, he had to pay a fine and then sit on the highway for a day with the dummy and a big sign saying he was an idiot or something. Then, he had to sell the dummy on ebay and give the money to a highway safety group.

Here in Dallas we have one of the more idiotic HOV lane setups. On I-30 every week day giant zipper machines go down the highway and move cement barriers over to take a lane of traffic away from the opposing side of the highway from the main congestion route. So, in the morning they move the barrier to take a lane from the east bound traffic out of Dallas and give it to the inbound downtown traffic. Then, in the afternoon vice versa so that in effect both lanes of traffic end up becoming congested no matter which way you try to go on 30. There is at least a physical barrier and traffic cops on each of the lane to make sure only the needful use it. When I used to work downtown I would carpool and take advantage of it and it was useful at times. However, that was only if the zipper machines weren't busted or somebody hadn't hit the moveable barricade system. Also, it is a single lane so getting stuck behind a city bus or somebody afraid to drive so close to a wall that they go 30 mph just totally sucks.

I have to say that the HOV-3 lanes on I-95/395 in Northern VA work pretty well. But these are physically-separated, two lanes (with sufficient shoulders in most places) and available to single-occupant traffic in the off-peak hours. I've lived here since before the separate lanes went in, and I have to say if I couldn't use the HOV to get to work, I'd have to move. The traffic is that bad otherwise. I do agree, though, that HOV done wrong is a net impediment. But if an area is able to spend the $$ to do it right, you can move more people.

- Eric.

The increase in accidents is most likely due to the difference in traffic flows: you've got one lane zipping along at near the speed limit right next to one or more which are slow to stopped. All it takes is a dummy, not paying attention behind a lane changer into or out of the HOV lane.

Then there's also the case of right hand HOV lanes, which violate the princple of "slower traffic keep right". I hate 'em, especially when I have to merge into them to take my exit. Again, never quite sure that I missed in a blind spot someone who's not paying attention.

I remember reversible lanes on Lake Shore Drive in Chicago in the '70s. There weren't any barriers, just periodic traffic light type arrows pointing down over each lane showing which lanes were available in your direction. Green okay, red oncoming traffic. I'm glad I never had to drive that on any regular basis.

They've a lot of them around Seattle and I'm of two minds about them. The one over the 520 bridge really does save time, if you have 3 in the car, however, it insanely has to cross 5 or 6 exits in the process.

The one on the 5 South through Seattle is just bonkers, no barriers, no differentiation and no point.