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HORIZONTE > viene de la pregunta 117
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HOW CONGESTED ARE THE ROADS? ARE THEY GETTING WORSE?
Congestion levels and the trends in congestion growth are important aspects of the database. Where and when congestion occurs is important within an urban network, as well as for comparing urban areas to each other. Comparisons should include considerations such as, areawide congestion levels tend to be worse in the larger urban areas, but there are some isolated pockets of very bad traffic congestion in smaller urban areas that rival some locations in larger cities. Comparisons with areas of similar population are usually more informative than broader comparisons.
Conclusions
In general, traffic congestion is worse in the larger urban areas than in the smaller ones. Traffic congestion levels have increased in every area since 1982. Congestion extends to more time of the day, more roads, affects more of the travel and creates more extra travel time than in the past. And congestion levels have risen in all size categories, indicating that even the smaller areas are not able to keep pace with rising demand.
The need for attention to transportation projects is illustrated in these trends. Major projects or programs require a significant planning and development time—10 years is not an unrealistic timeframe to go from an idea to a completed project or to an accepted program. At recent growth rates, the urban area average congestion values will jump to the next highest classification—medium areas in 2013 will have congestion problems of large areas in 2003.
The Travel Time Index is one of two primary measures of extra travel time for travelers. (See Exhibit 1). It measures the amount of additional time needed to make a trip during a typical peak travel period in comparison to traveling at free-flow speeds.
Travel delay per peak traveler is the other individual measure that provides estimates of the mobility levels (see Exhibit 2). The extra travel time per year can be related to many other activities and may be more relevant for some discussions.
The extra travel time each year is a combination of the extra travel time for each trip (as measured by the TTI), the trip distance and the number of trips. The effect of this difference is relatively modest in most areas—that is, the TTI and delay per traveler tell basically the same story. The rankings are similar and the pattern of growth or decline are about the same. In some areas, however, the two values lead to different conclusions.
Portland is one area where the multiple performance measures help illustrate the effect of the transportation and land use policies that are being pursued to create a denser urban area that is better served by public transportation. The Travel Time Index and the delay per traveler values have both increased since 1982, indicating an increase in congestion. The Travel Time Index for Portland grew faster from 1982 to 2003 than it has for the majority of the other areas in the Large urban group. Delay per traveler, however, has grown at a rate closer to the Large area average, indicating that delay has not grown as rapidly as the per-minute travel time penalties have declined. Perhaps the urban growth and transportation policies are encouraging shorter trips and travel on light rail and other modes.
Exhibit 1. Travel Time Index Trends Note: The Travel Time Index is a ratio of average peak period to free-flow travel time. A value of 1.30 indicates a free-flow trip of 20 minutes takes 26 minutes in the peak due to heavy traffic demand and incidents.
• The average TTI for all 85 urban areas is 1.37. Thus, an average 20-minute off-peak trip takes almost 27 minutes to complete during the peak due to heavy traffic demand and incidents.
• Congestion problems tend to be more severe in larger cities. The average TTI for each
individual population group ranges from 1.48 in the Very Large areas down to 1.10 in the Small urban areas.
• The average increase in the travel time penalty was 25 points (1.12 to 1.37) between 1982 and 2003. This gap ranges from 30 points in the Very Large group to 7 points in the Small population group.
• Twenty-eight of the 85 urban areas have a TTI of at least 1.30. Twenty-five of these urban areas are in the Very Large and Large population groups—they have populations greater than one million. Austin , Charlotte , and Tucson are the only areas with fewer than one million people and a TTI more than 1.30.
Exhibit 2. Delay per Peak Traveler Trends
• The average delay per peak traveler in the 85 urban areas is 47 hours.
• There are 17 urban areas with delay per peak traveler values in excess of 50 hours, showing
the effect of the very large delays in the areas with populations larger than 3 million.
• The average delay per peak traveler in the Large population group is about the same as the
average delay in the Very Large population group in 1987.
• The average delay per peak traveler in the Medium population group is about the same as the
average delay in the Large group in 1991.
HOW SHOULD WE ADDRESS THE MOBILITY PROBLEM?
Just as congestion has a number of potential causes, there are several ways to address the problem. Generally, the approaches can be grouped under four main strategies – adding capacity, increasing the efficiency of the existing system, better management of construction and maintenance projects, and managing the demand. The benefits associated with these improvements include reduced delay, and more predictable and lower trip times. Emissions may be reduced due to the reduction in demand or congestion, improved efficiencies and the change in the way travelers use the system. The locations of congestion may also move over time due to the new development that occurs or is encouraged by the new transportation facilities.
More Travel Options
While not a specific improvement, providing more options for how a trip is made, the time of travel and the way that transportation service is paid for may be a useful mobility improvement framework for urban areas. For many trips and in many cities, the alternatives for a peak period trip are to travel earlier or later, avoid the trip or travel in congestion. Given the range of choices that Americans enjoy in many other aspects of daily life, these are relatively few and not entirely satisfying options.
The Internet has facilitated electronic “trips.” There are a variety of time-shift methods that involve relationships between communication and transportation. Using a computer or phone to work at home for a day, or just one or two hours, can reduce the peak system demand levels without dramatically altering lifestyles.
Using information and pricing options can improve the usefulness of road space as well as offering a service that some residents find very valuable. People who are late for a meeting, a family gathering or other important event could use a priced lane to show that importance on a few or many occasions – a choice that does not exist for most trips.
The diversity of transportation needs is not matched by the number of travel alternatives. The private auto offers flexibility in time of travel, route and comfort level. Transit can offer some advantages in avoiding congestion or unreliable travel conditions. But many of the mobility improvements below can be part of creating a broader set of options.
Add Capacity
Adding capacity is the best known, and probably most frequently used, improvement option. Pursuing an “add capacity” strategy can mean more traffic lanes, additional buses or new bus routes, new roadways or improved design components as well as a number of other options. Grade separations and better roadway intersection design, along with managed lanes and dedicated bus and carpool priority lanes, can also contribute to moving more traffic through a given spot in the same or less time. The addition of, or improvements to heavy rail, commuter rail, bus system, and improvement in the freight rail system all can assist in adding capacity to varying degrees. In growing areas, adding capacity of all types is essential to handle the growing demand and avoid rapidly rising congestion.
Manage the Demand
Demand management strategies include a variety of methods to move trips away from the peak travel periods. These are either a function of making it easier to combine trips via ridesharing or transit use, or providing methods to reduce vehicle trips via tele-travel or different development designs.
The fact is, transportation system demand and land use patterns are linked and influence each other. There is a variety of strategies that can be implemented to either change the way that travelers affect the system or the approaches used to plan and design the shops, offices, homes, schools, medical facilities and other land uses.
Relatively few neighborhoods, office parks, etc. will be developed for auto-free characteristics— that is not the goal of most of these treatments. The idea is that some characteristics can be incorporated into new developments so that new economic development does not generate the same amount of traffic volume as existing developments. Among the tools that can be employed are better management of arterial street access, incorporating bicycle and pedestrian elements, better parking strategies, assessing transportation impact before a development is approved for construction, and encouraging more diverse development patterns. These changes are not a congestion panacea, but they are part of a package of techniques that are being used to address “quality-of-life” concerns—congestion being only one of many.
Increase Efficiency of the System
Sometimes, the more traditional approach of simply adding more capacity is not possible or not desirable. However, improvements can still be made by increasing the efficiency of the existing system. These treatments are particularly effective in three ways. They are relatively low cost and high benefit which is efficient from a funding perspective. They can usually be implemented quickly and can be tailored to individual situations making them more useful because they are flexible. They are usually a distinct, visible change; it is obvious that the operating agencies are reacting to the situation and attempting improvements.
In many cases, the operations improvements also represent a “stretching” of the system to the point where the margin of error is relatively low. It is important to capitalize on the potential efficiencies – no one wants to sit through more traffic signal cycles or behind a disabled vehicle if it is not necessary – but the efficiency improvements also have limits. The basic transportation system—the roads, transit vehicles and facilities, sidewalks and more—is designed to accommodate a certain amount of use. Some locations, however, present bottlenecks, or constraints, to smooth flow. At other times, high volume congests the entire system, so strategies to improve system efficiency by improving peak hour mobility are in order. The community and travelers can benefit from reduced congestion and reduced emissions, as well as more efficiently utilizing the infrastructure already in place.
Among the strategies that fall into this category are tools that make improvements in intersections, traffic signals, freeway entrance ramps, special event management (e.g., managing traffic before and after large sporting or entertainment events) and incident management. In addition such strategies as one-way streets, electronic toll collection systems, and changeable lane assignments are often helpful.
Freeway entrance ramp metering (i.e., traffic signals that regulate the traffic flow entering the freeway) and incident management (i.e., finding and removing stalled or crashed vehicles) are two operations treatments highlighted in this report. When properly implemented, monitored and aggressively managed, they can decrease the average travel time and significantly improve the predictability of transportation service. Both can decrease vehicle crashes by smoothing traffic flow and reducing unexpected stop-and-go conditions. Both treatments can also enhance conditions for both private vehicles and transit.
Manage Construction and Maintenance Projects
When construction takes place to provide more lanes, new roadways, or improved intersections, or during maintenance of the existing road system, the effort to improve mobility can itself cause congestion. Better techniques in managing construction and maintenance programs can make a difference. Some of the strategies involve methods to improve the construction phase by shortening duration of construction, or moving the construction to periods where traffic volume is relatively low. Among the strategies that might be considered include providing contractor incentives for completing work ahead of schedule or penalties for missed construction milestones, adjustments in the contract working day, using design-build strategies, or maintenance of traffic strategies during construction to minimize delays.
Role of Pricing
Urban travelers pay for congestion by sitting in traffic or on crowded transit vehicles. Anthony Downs (16), among many, has suggested this is the price that Americans are willing to pay for the benefits that they derive from the land development and activity arrangements that cause the congestion. But for most Americans there is no mechanism that allows them to show that they place a higher value on certain trips. Finding a way to incorporate a pricing mechanism into some travel corridors could provide an important option for urban residents and freight shippers.
A fee has been charged on some transportation projects for a long time. Toll highways and transit routes are two familiar examples. An extension of this concept would treat transportation services like most other aspects of society. There would be a direct charge for using more important system elements. Price is used to regulate the use and demand patterns of telephones, movie seats, electricity, food and many other elements of the economy. In addition to direct charges, transportation facilities and operations are typically paid for by per-gallon fees, sales taxes or property taxes. One could also include the extra time spent in congestion as another way to pay for transportation.
Electronic tolling methods provide a way for travelers to pay for their travel without being penalized by stopping to pay a fee. Electronics can also be used to reduce the fee for travelers in certain social programs (e.g., welfare to work) or to vary the fee by time of day or congestion level. Implementing these special lanes as an addition to roads (rather than converting existing lanes) has been the most common method of instituting pricing options in a corridor. This offers a choice of a premium service for a fee, or lower speed, less reliable travel with no additional fee.
Importance of Evaluating Transportation Systems
Providing the public and decision-makers with a sufficient amount of understandable information can help “make the case” for transportation. Part of the implementation and operation of transportation projects and programs should be a commitment to collecting evaluation data. These statistics not only improve the effectiveness of individual projects, but they also provide the comparative data needed to balance transportation needs and opportunities with other societal imperatives whether those are other infrastructure assets or other programs.
THE BIG PICTURE
There are many statistics in the Annual Mobility Study that can be applied to the search for solutions to mobility problems. It is very important, however, that the role of transportation in American cities be understood as one of many elements that determine the concept of “quality of life.” Road congestion is slow speeds caused by heavy traffic and/or narrow roadways due to construction, incidents, or too few lanes for the demand. It has corollaries in transit, sidewalks and the Internet. Over the last 20 years, traffic volumes have increased faster than road capacity. Alternative modes, new technologies, innovative land-use patterns, demand management techniques and operating treatments have not provided the needed relief either because they are not extensive enough, or they are not used for enough trips.
Urban residents trade off a variety of factors and cost elements in the search for the best situation. Transportation professionals, as well as developers, land planners, government officials, and others, are realizing that these trade-offs are made across a spectrum that might best be represented as several niche markets, rather than one or two large ones. Schools, shops, jobs, parking, health care and many other issues “compete” in some sense with transportation issues for attention and investment.
Some general conclusions can be drawn from the 1982 to 2003 database.
1. There is some good news — The urban road and transit systems have handled a lot more travel. Congestion time penalties are three to four times greater than in 1982, but almost double the amount of travel has been accommodated.
2. We are not doing enough —There aren't enough improvements to the system to keep congestion from growing. Hours of delay, the time of day and the miles of road that are congested have grown every year.
3. Roads are part of the solution. Areas that have added roads have seen congestion levels grow more slowly than other cities. More than 90 percent of urban peak-period person travel is on roads, and a significant amount of freight moves on roads.
4. But, roads cannot be the only solution in most cities. It will be difficult for most big cities to address their mobility needs by only constructing more roads. This is partly a funding issue—transportation spending should probably double in larger cities if there is an interest in reducing congestion. In some corridors or some activity centers, the additional transportation needed is for walk, bike, and public transportation modes that are more consistent with the nearby developments. It is also; however, an issue of project approval. Many Americans do not want major transportation projects near their home or neighborhood. It is difficult to imagine many urban street and freeway corridors with an extra 4, 6 or 8 lanes, but it may be required if the goal is to significantly reduce congestion by adding roads.
5. Transit improvements, better traffic signal operations, aggressive incident management programs, adjusted work hours, telecommuting and a range of other efficiency options are absolutely vital components of an overall solution. Individually they do not seem to offer the promise of large increases in person carrying capacity for the current system. But their cumulative effects can be a substantial improvement and may represent feasible strategies in areas where no other solutions are viable. The effect of some of these treatments was included in the Annual Mobility Report for the first time this year.
6. Policy options, including value pricing, peak-travel restrictions, education programs, innovative mortgage arrangements, and a variety of other strategies not evaluated in this report present opportunities for improving transportation. Some of these are difficult to get approved in the political and/or public approval stages. They require some changes in the way transportation services are viewed and some changes in the way we live and travel. But for some travel markets in some areas, they may provide the right combination of service and price.
7. Reliability in transportation service is emerging as an important issue. The Annual Mobility Report database will be expanded in the future to include estimates and directly collected data about the variations in travel time, as well as the averages.
Some of the solution lies in better management—improving on practices that are already known and utilized and developing new expertise. In the 1950s and 1960s, state highway agencies managed the construction of a large highway system. In the 1970s transportation agencies tried to improve the system by managing the supply, and in the 1980s a variety of transportation and planning agencies and private sector companies started to manage the demand patterns. In the 1990s, the management effort was focused on better system operations for roads and transit.
• Most large city transportation agencies are pursuing all of these traditional projects and programs. The mix may be different in each city and the pace of implementation varies according to overall funding, commitment, location of problems, public support and other factors. It seems that these same agencies could also provide some information about the expected outcome of the transportation system improvements. Big city residents should expect congestion on roads for 1 or 2 hours in the morning and in the evening. The agencies should be able to improve the performance and reliability of the service at other hours and they may be able to slow the growth of congestion, but they cannot expand the system or improve the operation enough to eliminate congestion.
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