• Study
  • 42
HOV yellow stickerWhodathunk that banning hybrid vehicles from California's High Occupancy Vehicle (HOV) lanes would lead to additional congestion on the state's highways and even longer commute times? Transportation engineers at the University of California, Berkeley did, and that's why the University's researchers are now pushing for HOV access to be granted to more vehicles, not less.

UC Berkeley researchers recently discovered that after single-occupant hybrid vehicles were booted out of HOV lanes, traffic increased for all of the state's drivers. The program, which kicked off in 2005 and ended July 1, 2011, granted some 85,000 owners of hybrid vehicles access to California's carpool lanes, but critics argued that solo drivers of hybrids were clogging up the lanes designed for carpooling.

Researchers at UC Berkeley used "traffic flow theories and six months of data from roadway sensors measuring speed and congestion along all freeway carpool lanes in the San Francisco Bay Area" to assess the traffic situation. Michael Cassidy, UC Berkeley professor of civil and environmental engineering and Kitae Jang, a doctoral student at the University, arrived at this conclusion:
Our results show that everybody is worse off with the program's ending. Drivers of low-emission vehicles are worse off, drivers in the regular lanes are worse off, and drivers in the carpool lanes are worse off. Nobody wins.
Currently, the only type of single-occupancy vehicles allowed in California's HOV lanes are federally approved Inherently Low Emission Vehicles (ILEVs), including hydrogen fuel cell, electric-only and compressed natural gas vehicles with white stickers. According to the California Air Resources Board (CARB), only 14,000 vehicles statewide have qualified for the coveted white sticker, which UC Berkeley researchers claim is not nearly enough to get traffic flowing more freely again.
Show full PR text
Kicking hybrids out of carpool lanes backfires, slowing traffic for all

The end of a California program granting free access to carpool lanes by solo drivers of hybrid cars has unintentionally slowed traffic in all lanes, according to transportation engineers at the University of California, Berkeley.

UC Berkeley transportation researchers found that after single-occupant hybrids got kicked out of the carpool lanes, traffic slowed for everyone.

The program, which began in 2005 and ended on July 1, gave consumers an extra incentive to buy low-emission cars. By 2011, some 85,000 low-emission vehicles had gotten the coveted yellow stickers that gave them entry into the carpool lanes, but critics of the perk argued that solo drivers of hybrid cars were clogging up the lanes for carpoolers.

Researchers at UC Berkeley's Institute of Transportation Studies (ITS) used traffic flow theories and six months of data from roadway sensors measuring speed and congestion along all freeway carpool lanes in the San Francisco Bay Area. They used the information to predict the impact on vehicle speed of the hybrids' removal from carpool lanes. Additional data collected after the program's July 1 expiration supported their predictions.

Michael Cassidy, UC Berkeley professor of civil and environmental engineering, and Kitae Jang, a doctoral student in civil and environmental engineering, presented their analysis in a new report released by ITS.

"Our results show that everybody is worse off with the program's ending," said Cassidy. "Drivers of low-emission vehicles are worse off, drivers in the regular lanes are worse off, and drivers in the carpool lanes are worse off. Nobody wins."

A carpool lane along a four-mile stretch of I-880 in Hayward, for instance, saw a 15 percent reduction in speed after single-occupant hybrids were expelled after July 1.

The counterintuitive results reflect dual – and opposing – influences on traffic speed in the carpool lanes, the researchers explained. One factor is the presence of additional cars, including hybrids, which slow down traffic. One might think that moving vehicles out would allow the remaining cars in the lane to go faster.

But the data show that traffic speed in the carpool lane is also influenced by the speed of the adjacent lanes. Moving the hybrids into the neighboring lanes increases congestion in those lanes, which in turn slows down the carpoolers.

"As vehicles move out of the carpool lane and into a regular lane, they have to slow down to match the speed of the congested lane," explained Jang. "Likewise, as cars from a slow-moving regular lane try to slip into a carpool lane, they can take time to pick up speed, which also slows down the carpool lane vehicles."

Human nature likely plays a role, too, the researchers said. "Drivers probably feel nervous going 70 miles per hour next to lanes where traffic is stopped or crawling along at 10 or 20 miles per hour," said Cassidy. "Carpoolers may slow down for fear that a regular-lane car might suddenly enter their lane."

Currently, the only single-occupancy vehicles allowed in California's carpool lanes are federally approved Inherently Low Emission Vehicles, or ILEVs, such as hydrogen fuel cell, 100 percent battery electric, and compressed natural gas vehicles with white clean air vehicle stickers. According to the California Air Resources Board, only 14,000 vehicles in the state have qualified thus far.

A new program, pending federal approval next January, will allow 40,000 super-clean plug-in-hybrids or hydrogen-powered internal combustion engine vehicles to claim green clean air vehicle stickers and enter carpool lanes.

But the researchers predict that this will not be enough. They argue that freeway traffic conditions will improve for everyone by increasing, not decreasing, the numbers allowed access to carpool lanes.

"I think we need to start managing carpool facilities in a smarter way, and letting those hybrids back in the carpool lane would be a good first step," said Cassidy. "And given the way that regular-lane speeds influence carpool lanes, added efforts to alleviate congestion in regular lanes could benefit all drivers."

The work was supported by the UC Berkeley Center of Excellence for Future Urban Transport.


I'm reporting this comment as:

Reported comments and users are reviewed by Autoblog staff 24 hours a day, seven days a week to determine whether they violate Community Guideline. Accounts are penalized for Community Guidelines violations and serious or repeated violations can lead to account termination.


    • 1 Second Ago
  • 42 Comments
      EVnerdGene
      • 3 Years Ago
      I've got one of these stickers on my car (expired Jan. 1, 2011 - - - BTW). Scared sheetless to use the lane when the other seven lanes are crawling at 0 to 3 MPH, and I'm going 80 with a hybrid Highlander about 8 feet from my rear bumper with his high beams on. Then, an Escalade pulls from a near stop into the carpool lane - cause he/she just can't take it any more. I've seen horrific accidents with this scenario - high speed accident in bumper-to-bumper traffic. WTF happened?
        EZEE
        • 3 Years Ago
        @EVnerdGene
        Interesting point. At first, I saw no issue with allowing hybrids into those lanes, but, can one call an escalade hybrid 'green?'. I know I am the radical right winger here...but...an escalade? I couldn't even call that green even if I was trying to be annoying.
      nosoupforyou
      • 3 Years Ago
      I think it's too soon to measure the effects of yellow/white HOV stickers. Once supply starts keeping up with demand, EV's might replace many of the hybrids that have been enjoying HOV privileges. I would bet that a significant number of people originally bought hybrids because of lower fuel costs and HOV access. If that's true, commuters might trade up for an EV to enjoy the same benefits that they had with the hybrid and at that point the traffic flow would even out again.
      mexicanjetta
      • 3 Years Ago
      Correction: The existence of HOV lanes slows everyone down.
        Noz
        • 3 Years Ago
        @mexicanjetta
        No correction....the unbound amount of idiots on the road trying to use HOV lanes when they shouldn't slows everyone down.
        tump
        • 3 Years Ago
        @mexicanjetta
        Agree that Highway 101 has a negative effect in HOV time. Carpooling is not an option for most of the tech industry. HOV does not encourage carpooling if carpooling is a no-op to start with. The net effect is that 101 becomes one fewer lanes during the peak traffic time.
        Letstakeawalk
        • 3 Years Ago
        @mexicanjetta
        Bingo
        paulwesterberg
        • 3 Years Ago
        @mexicanjetta
        Especially when they are underutilized. If more people carpooled then the lanes might help to move more people get to their destinations quickly, but it is a delicate balance. If many people carpool then the hov lane will be as slow as the other lanes and carpoolers might feel as though there is no benefit to carpooling.
        Letstakeawalk
        • 3 Years Ago
        @mexicanjetta
        Proper utilization is key, and sadly, the HOV lanes are generally underutilized. Here's an older study: "1. HOV excess capacity: How much additional flow can an HOV lane support while maintaining free flow speed of 60 mph? 2. Overall congestion: If an HOV lane were to be opened to general traffic, would the overall congestion be decreased? 3. Person throughput: Does an HOV lane increase the total throughput in persons per hour? 4. Carpooling response to travel-time savings: How many SOV drivers would switch to carpooling if travel time on non-HOV lanes doubled?" "The analysis presented here suggests that in the Bay Area, instead of improving mobility, HOV lanes exacerbate the congestion problem: HOV lanes suffer a capacity drop of 400 vehicles/hour; they increase congestion overall; they do not significantly increase the throughput of people; and they do not encourage carpooling." http://robotics.eecs.berkeley.edu/~varaiya/papers_ps.dir/HOV.pdf
      Derek
      • 3 Years Ago
      Because HOV lanes lack any form of congestion management, they will always be underutilized or overutilized. They are incapable of reducing traffic congestion in the long term.
      Mike
      • 3 Years Ago
      One more thing - northern California HOV lanes are only 5-9am and 3-7pm M-F with two people per vehicle. Southern California HOV lanes are mostly 24/7 and 3 people per vehicle. So, the policy situation is clearly different between the metro areas, yet the sticker rules are state-wide.
      Nick
      • 3 Years Ago
      I fail to see how removing Hybrids from HOV laves could increase traffic in those HOV lanes.
      Dan Frederiksen
      • 3 Years Ago
      that's the problem with incentives rather than actually making it happen. if the people don't follow the incentives it can backfire. if Steven Chu weren't so incompetent and had built efficient demonstrator vehicles and facilitated factories we wouldn't need to hope incentives will work. we wouldn't need to rely on known villains to be good.
        EZEE
        • 3 Years Ago
        @Dan Frederiksen
        Totally lost on all points. Can you expand?
      • 3 Years Ago
      Minor correction: single-occupancy motorcycles are also allowed in HOV lanes.
      • 3 Years Ago
      I bet if they redid the study, this time allowing single occupant Hummers in the HOV lanes, that would also speed up traffic for everyone..... The point is that HOV lanes are used below capacity, to provide a quicker commute for whatever type of vehicle is being favored. If we got rid of the HOV lanes totally, and let everyone use whatever lane they wanted, traffic would be even quicker for everyone. But the point is to favor a priviledged group, not to benefit everyone equally. That's what liberal governments do, they hand out favors to special interests....
      • 3 Years Ago
      So moving excess cars from the standard lanes to the less used HOV lanes increases the net throughput? Wow, genius. Would it still work if instead of white stickered cars they made it blue cars? Probably. Hey there's an idea "Blue Car Mondays, Red Car Tuesdays, White Car Wednesdays, Silver Car Thursdays and Black Car Fridays". That should help.
      • 3 Years Ago
      No special HOV lanes! Freeing up those lanes would allow for 20% more traffice flow. It's idiotic for the lanes to sit vitrually empty when the other lanes are virtually girdlocked. Such stupid government mis-management.
      • 3 Years Ago
      For sure, it seems counter intuitive. If viewed from the other side of the coin - it makes some sense, that is, allowing more cars into the HOV (car pool) lanes allows less congestion in the non-HOV lanes because there are less cars. And because the HOV lanes are not congested to start with - allowing more cars to be in those lanes may not increase the congestion noticeably. But one of the arguments offered for the slow down effect in all lanes when hybrids are taken out of the HOV lanes is that adjacent traffic in the non-HOV lanes (now increased) affects the HOV lanes slowing them down. But can't you argue that putting more vehicles in the HOV lanes negatively affects the flow in the non-HOV lanes. Adjacent traffic rationale is a two edged sword - isn't it? Another argument is human nature. "Human nature likely plays a role, too, the researchers said. "Drivers probably feel nervous going 70 miles per hour next to lanes where traffic is stopped or crawling along at 10 or 20 miles per hour," said Cassidy. "Carpoolers may slow down for fear that a regular-lane car might suddenly enter their lane." Sounds more like an argument to eliminate the car pool lanes. The 'fear' is there irrespective of the number of hybrids in the HOV lanes. One wonders too just how emissions can be reduced when the regular lanes are jammed and the car pool lanes virtually empty. The 'fear' is rare given the cost of the ticket. The adjacent traffic and human nature are better arguments for eliminating the car pool lanes. Although I haven't lived in SF Bay Area for several years - when I was driving on a daily basis it was easy to conclude that traffic congestion was not eased but increased by the HOV lanes. That is narrowing the number of lanes available to regular traffic is bound to increase congestion in the remaining lanes. But for any argument to be accurate - wouldn't it be necessary that there be somewhat of a high volume of hybrids using the HOV lanes or even on the road in the Bay Area? One might notice that the number of hybrids involved was never mentioned. Eliminating HOV lanes is a more logical solution to congestion. Sounds more like a graduate student project that fills in his or her expectations with the data needed. An excellent resource - see http://ops.fhwa.dot.gov/publications/fhwahop09029/index.htm especially http://ops.fhwa.dot.gov/publications/fhwahop09029/sec4_policy.htm for
        • 3 Years Ago
        Here's another thing that's counter-intuitive It's better to have hybrids stuck in traffic than zooming by in HOV lanes. That is because the hybrids generally are running with the engine off and creeping along on batteries. This is actually where hybrids excel. At first the HOV incentive was just to get more of them on the road and help improve air quality. Now there are significant numbers of them, and fuel savings incentives are enough just by themselves. EVs are now in the position that hybrids were a decade ago.
          EZEE
          • 3 Years Ago
          Wow...you people are making some great points!
    • Load More Comments