The Chronicle noted recently that the last remaining section of the Southwest Freeway reconstruction — an HOV ramp off of Milam — had opened, completing a 115-mile HOV lane system.

The first HOV lane in Houston opened on I-45 north in 1979. It was a temporary facility, separated from other traffic with plastic pylons. The first permanent lanes, on I-45 north and the Katy Freeway, opened in 1984. They were followed by the Gulf Freeway, opened 1988-1997, 290 in 1988, the Southwest Freeway as far as Shepherd in 1989-1992, and the Eastex Freeway in 1999-2004. At first the HOV lanes were designed for buses and licensed carpools only (which is why onramps to the older lanes can be so hard to find) but soon they were opened up to any car with 2 or more people (3 or more on the Katy). Erik Slotboom’s Houston Freeways has an excellent history of the HOV system.

Lots of cities have HOV lanes. Typical HOV lanes are simply the left-hand lane of the freeway, marked off with white lines and designated with signage. These lanes work, but they have problems. Enforcement is difficult — a SOV using the HOV could simply merge back into the mainlanes upon spotting a police officer. The lanes don’t move as fast as they could since some HOV lane drivers won’t drive at full speed if the lane to their right is backed up. And for buses to use the lane, they have to slowly merge across multiple lanes of backed-up traffic.

Houston’s HOVs are unique in that they are separated from the mainlanes by barriers. That keeps HOV traffic moving and makes enforcement easier. And the HOV entrances and exits are separated, too, in the form of flyers connecting to transit centers and dedicated Downtown on- and off-ramps.

I’ve talked about the HOV lanes before in the context of MetroExpress buses. Those buses — one of the best suburban commuter transit systems in the country — carry about 40,000 people on an average weekday. Non-METRO buses (Woodlands Express, Trek, and intercity services), vanpools, and carpools carry another 80,000. That’s a total of 120,000 daily trips, roughly the same as 24 freeway lanes.

The HOV lanes started as an experiment. Now they’re an established part of Houston’s transportation system. They’ve also helped shape the city: the additional people-moving capacity into Downtown has helped keep Downtown competitive as an employment center (while Post Oak, which is is not as well served and much more congested, hasn’t seen a new office building since the 1980s). The HOVs have also boosted transit use: the HOV lane buses account for 15% of METRO’s ridership, and 40% of Downtown employees take transit.