HOV Lanes: When Two-plus Becomes Three-plus

Anyone who carpools during peak traffic hours on the 290 HOV lane knows how the traffic crawls – at certain times and in certain spots. Several of you have written in, asking when we’re going to change the occupancy requirements in the peak morning and evenings hours from two or more occupants to three or more occupants.

“It’s being considered, but we don’t have a timetable established,” said Loyd Smith, director of transportation systems at METRO. “It’s a significant change because those people who are using the HOV lane in the 5 p.m. to 6 p.m. hour with two persons would be impacted. There’s a significant number of those. They would either have to get in before 5 p.m. or get a third person.”

But the traffic management gurus here know that the Houston traffic can back up and be as slow as the main lanes. In fact, they have assigned a grade “D” to that lane. Traffic engineers give grades to rank the type of traffic flow (A to F, just like school report cards).  A level of service D means “approaching unstable traffic flow; minor incidents cause traffic queing.”

 When a lane rates a D, it’s time to do something.

  Level of Service (LOS) Definitions for Roadways

Source:  2000 Highway Capacity Manual

For U.S. 290, METRO has consistently measured 1,500 vehicles an hour from 5 p.m. to 6 p.m. In the mornings from 7 a.m. to 8 a.m., when the occupancy rules require three or more persons, the lane carries 1,350 vehicles an hour.

Before the morning rules were changed a few years ago, the volumes carried from 7 a.m. to 8 a.m. were higher. “The difference illustrates a downside of changing to a three-person requirement: The use of the lane will be reduced somewhat at the time when the congestion and delay in the mainlane is at its worst,” explained Smith.

“We know from experience that 1,500 vehicles per hour is near a “tipping point” where a small increase in volume can begin to negatively affect travel speeds,”  Smith added. “In general roadway planning, capacity and volume carried a higher weight in the evaluation process than speed.”

But at METRO, we value speed, too. After all, if buses – which use the HOV lanes – can’t meet their schedules on time, we’ve got a busload of unhappy passengers.

“For us, because the travel time savings and reliability are the service we’re providing, we’re sensitive to that to a higher degree,” Smith said. But he noted that the overall travel time savings on the HOV lane is the key evaluation factor, not just maintaining operating speeds at or near the speed limits over the entire length of the trip.

 “Even on the a day when the 290 HOV lane traffic has a segment that drops to 30 mph or less, we often find that the overall time savings from the Cypress area to downtown will still be between 15 to 20 minutes,” Smith said.  

Although the Texas Department of Transportation owns the roads and the dirt, METRO manages and maintains the HOV lanes.

Take a look at the numbers and you’ll see that HOV lanes have grown successfully in the past eight years. System-wide, all HOV lanes carry 45,000 vehicles a day. Of those, 94 percent are carpools, 2 percent buses, 2 percent vans and 2 percent motorcycles. System-wide, the HOV lanes carry 135,000 passengers daily.

Only 65 percent of those are in carpools; 32 percent on buses; 3 percent on vans and 1 percent on motorcycles. From 1998 to 2006, there’s been a 70 percent increase in vehicles and volume, said Smith.

So what factors go into deciding when an HOV lane changes from allowing carpools with two or more to vehicles with at least three or more?

Smith says four elements come into play:

• Consistent degrading of travel times. “The trends have to point to this – that it is not incident-based or short-term because of a construction detour. It has to be a true trend that consistently impacts traffic,” said Smith.

• Rigorous enforcement of HOV lanes.

If cheaters with less than the required number of occupants sneak on, they slow the lane down for everyone else. The METRO Police’s use of motorcycle cops to catch the bad guys (as described in Tuesday’s blog),  along with the public reporting cheaters on the HERO Hotline,  are both helping to increase the number of citations issued to HOV violators.

• Impact on METRO buses.

METRO analyzes what’s happening with buses that use the HOV lanes, both from a financial and a service perspective.  “Bus users are just like the carpoolers,” said Smith. “If we hear from our customers and our bus supervisors who are measuring more late buses, those things are concrete evidence that the speeds are being affected,” said Smith.

• The physical environment of the HOV lane itself.

Is construction being planned near or around it? For example, there have been numerous changes to the Katy Freeway (and the Katy HOV lane) over the past few years as TxDOT’s reconstruction project has proceeded.

For the U.S. 290 HOV lane users traveling from downtown, the progress of the Katy Freeway construction, the changes to the Old Katy Road near the Northwest Transit Center and the loss of a ramp directly connecting the mainlanes to the 290 HOV entrance have all caused afternoon travel times to fluctuate.

 Because METRO considers a change to a 3+ rule a permanent change, it’s important to confirm that the state of the nearby roadway capacity is stable at the time of the change.

“If I knew that ramp were going to be opening up tomorrow, that would attract more people to the 290 because presently to get on 290 HOV, you must travel on Katy Road through the Northwest Transit Center or the brand new ramp built by TxDot,” said Smith. “That has somewhat of a negative effect on the number of people who use the HOV lane because there have been delays due to construction. If (TxDot) opened the ramp, the volume would jump up more. We would be at that tipping point and go forward.”

“When - in the timeline of a constantly changing travel environment - do you pull the trigger and make an occupancy change when it’s warranted? Ultimately, it’s a judgment call,” said Smith, agreeing that it’s part science, part art. “We want the lanes to operate and to operate well.”