And in recent years there have been growing calls to substitute commuter rail, light rail and high-speed rail projects for road projects. But even if money is spent on rail instead of on roads, the rosiest predictions of Southern California planners say just 9 percent of commuters will be commuting by mass transit or bike in The reality for Orange County and Southern California is that, even if transportation funding is diverted to rail and transit projects, over 80 percent of people will still commute in cars in Thus, any smart long-range infrastructure plan must focus on reducing traffic congestion.
Orange County is the pioneer of the approach the region should be taking. The two 91 Express Lanes handle 49 percent of the peak-direction throughput on the six-lane expressway, even though they represent only 33 percent of the physical lane capacity. These lanes take a simple concept — users pay — and show why it can be so effective. If you want to pay to move into the free-flowing lane, you can. Policymakers often just presume that constructing an HOV lane is more effective in reducing pollution than constructing another general-purpose lane.
However, it does not necessarily work out that way. The main source of reduced emissions is reduced congestion, not reduced trips. Multiplied by the thousands of vehicle trips that benefit from congestion reduction, these harmful emissions could be reduced by hundreds of thousands of grams per day. In comparison, a light passenger vehicle traveling at 20 mph emits 21 grams of ROG and grams of CO on a mile trip. Eliminating one such trip certainly provides greater environmental benefit than reducing congestion for that one vehicle.
But, if overall benefits of trip reduction are to exceed overall effects of reduced congestion, thousands of trips would have to be eliminated. But the evidence shows that the addition of an HOV lane does not greatly motivate solo drivers to rideshare, so it is difficult to eliminate trips. When freeway expansion is considered, clearly the strategy that best reduces congestion will also best reduce harmful emissions. The question, then, is whether adding an HOV lane will reduce congestion more effectively than adding a general purpose lane.
The advantage of adding an HOV lane is that, as long as some delay remains on the other lanes, it does reduce some vehicle trips. The disadvantage is that the freeway is only partially used. My research shows that HOV lanes perform better than general-purpose lanes only when there is initially long delay, thus motivating solo drivers to rideshare, and the initial proportion of HOVs is fairly high, resulting in greater use of HOV lane capacity.
Figures compare the effectiveness of adding an HOV lane to adding a general-purpose lane on a three-lane highway, with average peak-period person-delay as the indicator. An average high-occupancy vehicle is assumed to have 2. The vertical axis represents the difference in average person-delay between the added HOV lane and the added general-purpose lane. When the value is positive, it means more person-delay would occur on an added HOV lane than on an added general-purpose lane so a general-purpose lane would be more effective in reducing congestion.
The right horizontal axis represents the proportion of preexisting high-occupancy vehicles on the highway before a new lane was added. The left horizontal axis is a coefficient that estimates the likelihood of solo drivers shifting to high-occupancy vehicles, depending on how much travel-time they save by using the HOV lane. The higher the number The lower the number Figures 1 and 2 show results for highways with initial maximum delays of 15 minutes and 25 minutes, respectively.
Nowhere do the graphs drop below zero on the vertical axis. That is, in all cases an added general-purpose lane would cause either the same amount of person-delay or less person-delay than an added HOV lane, even if the initial proportion of high-occupancy vehicles were high, and even if solo drivers shifted to high-occupancy vehicles easily.
Figure 3 shows results for highways with initial maximum delays of 35 minutes. Only when the initial proportion of high-occupancy vehicles is 20 percent or more does the graph drop below zero.
That is, only then would an additional HOV lane offer less person-delay than an additional general-purpose lane. Advocates of HOV lanes might argue that expected population and economic growth will make a new HOV lane a better choice, in ten years, then would an additional general-purpose lane will be lost. Besides, the expected growth may not occur.
Who is responsible for building and operating HOV lanes? How are HOV lanes enforced? What happens to drivers who violate HOV lane rules? Why do some HOV lanes allow a minimum of two passengers per vehicle, while others require three?
Do children and infants count as passengers? Why do HOV lanes often appear empty? Why are motorcycles allowed in some HOV lanes? What about two-seater vehicles? Are they allowed to use HOV lanes with three-person requirements? Are other vehicles prohibited from using HOV lanes, even with the appropriate number of passengers? What is the safety record of HOV lanes? Do HOV lanes operate only during rush hours? Are HOV lanes effective? What are some of the measures of effectiveness?
Can HOV lanes be put to other uses as well? Some say that HOV lanes aren't as good for air quality as they were originally thought to be. Is that true? There are some areas with more than one HOV lane. Are these facilities coordinated with one another?
How can I learn more about HOV facilities? An HOV lane, sometimes called a carpool lane, is a special lane reserved for the use of carpools, vanpools and buses. They are usually located next to the regular, or unrestricted, lanes.
These special lanes enable those who carpool or ride the bus to bypass the traffic in the adjacent, unrestricted "general purpose" lanes. HOV lanes are intended to incentivize throughput move more persons per car, per lane and save time for car-poolers and bus riders by enabling them to bypass the areas of heaviest traffic congestion. Because most drivers, especially during rush hours, are driving alone, the HOV lane is seldom congested. Giving car-poolers a reliable and congestion-free ride during rush hour serves as a strong incentive for ridesharing HOV lanes also provide commuters a needed alternative to congestion, which is not always possible if all lanes are opened to everybody.
HOV lanes benefit not only those who share the ride, but all drivers, taxpayers and area residents. First, by encouraging high-occupancy travel that is, more passengers in fewer vehicles these lanes can help ease congestion in heavily-traveled metropolitan areas. Second, by reducing the traffic burden on highways, they can help defer costly expansion projects. Third, by reducing the number of vehicles on the road, HOV lanes can help reduce the extent of exhaust emissions and contribute to cleaner air.
Most state Departments of Transportation and local agencies sponsor programs to support ridesharing. These programs include ride matching databases to help commuters find carpool partners; coordination of employer ridesharing programs; vanpooling programs, and up-to-date information on transit alternatives throughout the area.
Contact your state Department of Transportation to learn about its ridesharing program. While the most common type of HOV facility is a carpool lane, other types of HOV facilities include exclusive HOV ramps, bypass ramps at ramp meters, toll plazas and ferry docks, bus lanes and commuter parking lots with direct connections to HOV lanes.
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