TESTIMONY ON
PEAK-HOUR TRAFFIC CONGESTION
By Anthony Downs
Senior Fellow
The Brookings
Institution
Presented before
the Senate Environment and Public Works Committee
Dirksen Senate
Office Building, March 19, 2002
My name is Anthony Downs, and I am a
Senior Fellow at the Brookings Institution.
I am the author of the 1992 book STUCK IN TRAFFIC, which deals with the
causes of and possible remedies for peak-hour traffic congestion, and which I
am now revising for a second edition.
The views I state here are solely my own, and not those of the Brookings
Institution, its Trustees, or its other staff members.
My comments will consist of a series of major
points, with some supporting discussion of each. These points are focused on a realistic view of the nature of
traffic congestion, both present and future, and what actions might be taken to
relieve it.
The Positive Social
Function of Traffic Congestion
Most people regard peak-hour traffic
congestion as an unmitigated evil, but that viewpoint is incorrect. Congestion is a vital de facto device we use
to ration the scarce space on our roads during periods when too many people
want to use that space at once. In
effect, congestion is a balancing mechanism that enables us to pursue many
other goals besides rapid movement -- goals American society values
highly. Those goals include having a
wide variety of choices about where to live and where to work, working during
similar hours so we can interact with each other efficiently, living in
low-density settlement patterns, and enjoying highly flexible means of movement
-- that is, private vehicles. The only
other possible means of rationing highway space when too many people want to
use it would be (1) charging high tolls to keep many people off the roads then,
which most Americans decisively reject because it would unduly favor the
wealthy, or (2) spending enormously more money to build enough roads to handle
all peak-hour traffic without delays.
But that would require turning metropolitan areas into virtual cement
slabs -- which would be environmentally undesirable and prohibitively
costly. Since we wisely reject those
means of allocating road space, we must use delays from overcrowding in order
to pursue the other goals we want to achieve.
So congestion makes possible large-scale social benefits as well as the
costs of delay on which most people focus when they think about it.
Peak-Hour
Congestion Is Inevitably Going to Get Worse All Over the World
Because it performs a critical
rationing function, traffic congestion is inescapable in large modern and
modernizing metropolitan areas all over the world. In fact, it is certain to get worse in almost all of those areas,
because populations are growing, and higher fractions of those increased
populations will be using private vehicles for movement. So the biggest future ground transportation
problem everywhere in the world will be coping with immense increases in the
number of vehicles in use. In the
United States, since 1980, we have added 1.2 cars, trucks, or buses to our
registered vehicle population for every one person added to our human
population. (This ratio was 1.49 to 1
in the 1980s, but declined to 1 to 1 in the 1990s.) In addition, we have increased the average number of miles each
vehicle is driven each year. Hence
total vehicle miles traveled increased by 72 percent from 1980 to 1998; whereas
our total population increased by less than 20 percent.
In the 1990s, we added 32 million
persons to our human population, and we may do so again in each of the next two
decades. Unless American behavior
changes radically, that means we will add as many as 64 million more vehicles
to our registered vehicle population by 2020.
Coping with the added traffic generated by this increase will be the
main challenge to our ground transportation policy in the next two
decades. Without doubt, traffic
congestion will get worse because of these population dynamics.
Peak-Hour
Congestion Is Almost Impossible to Eliminate Once It Has Appeared
Once peak-hour congestion appears on a
major roadway, it cannot be entirely eliminated by expanding the capacity of
that road, though its duration can be reduced.
That is because of the operation of the Principle of Triple
Convergence. If the road’s capacity is
expanded, traffic at first moves faster on that road. But soon people realize this, and start altering their
behavior. Drivers converge on the
expanded road from other routes they have been using to escape congestion, from
other times they have been using to avoid it, and even from other modes like
buses or trains. Soon the increase in
vehicles overloads the expanded road once again until traffic at the peak hour
is moving no faster than before. True,
the peak period may be shorter and the number of vehicles carried by the road
each hour may be larger, since the road’s capacity has been expanded. But traffic during the peak period will move
no faster than before the road’s capacity was increased. This means we cannot “build our way out of
congestion” by expanding road capacity on crowded expressways or other key
routes, once peak-hour congestion has appeared on them.
Another obstacle to “building our way
out of congestion” is that expanded roads may attract more new development
along their routes, generating more traffic than before the roads were
expanded. This is particularly likely
in fast-growing metropolitan areas.
Yet American
Society Will Need to Spend Heavily on Road Construction in the Future
Though we cannot build our way out of
existing congestion, large future spending on road capacity will certainly be
needed for two reasons. The first is to
maintain existing roads and bridges, many of which are in serious need of
repairs. Existing roadways are almost
certain to carry much more traffic in the future than any new roads built,
since the former serve large already-existing population centers; whereas new
roads will mainly serve lower-density growth areas. That makes improving existing roads a very high priority goal.
The second reason is to provide
mobility for new-growth areas, most of which will be located on the peripheries
of existing metropolitan regions. As
settlements expand outward, new roads will be necessary to create mobility for
their residents. Some advocates of “smart
growth” argue that most future population increases should be accommodated by
raising densities in already-built-up areas, rather than by expanding outward
in more “sprawl.” Some increases in
density will probably occur. But residents
of most American neighborhoods do not want higher densities and will resist
them vehemently, as experience clearly shows.
Therefore, the chance that even a majority of future growth will occur
through higher densities rather than though more outward development is very
small. A lot more roads will be needed
to provide mobility for residents of those new outlying areas.
Emphasis on
Measuring the Aggregate Costs of Congestion Tend to Exaggerate Its Pain
The Texas Transportation Institute
(TTI) has developed useful measures of traffic congestion, and changes in it
over time, for a large number of major metropolitan areas. But the way these measures are expressed
tends to exaggerate the amount of pain inflicted upon the American driving
public. TTI estimates that the greatest
annual delay from congestion in 1999 per person occurred in the Los Angeles
region and equaled 56 hours; the average annual delay per person for 68 regions
was 36 hours. 56 hours is a whole week
of 8-hour days, and that certainly seems like a lot of wasted time. But when divided by 240 working days, and
then by 2 for two trips per day, the average delay per person was 7.0
minutes per one-way commuting trip in the worst case (Los Angeles) and only 4.5
minutes for all 68 regions. When viewed this way, the “excess” time spent commuting does not
seem so immense, though we all tend to remember the worst delays as being close
to the average. This is the price we
pay for rationing the scarce space on our roadways during peak hours so we can
pursue all those other goals I mentioned at the outset of this testimony.
Americans Strongly
Prefer Moving in Private Vehicles to Using Public Transit
Most Americans prefer using private
vehicles for mobility instead of public transit because private vehicles have
many superior traits. These include
greater comfort, more flexibility as to timing, ability to perform several
tasks on one trip, greater speed, more privacy, and -- if parking is free -- possibly
lower costs. The average automobile
commuting trip in 1990 was about 22 minutes; whereas the average bus commuting
trip was 36 minutes and the average rail commuting trip was 45 minutes. Thus, any major shift from private vehicles
to transit would increase the average amount of time spent commuting.
The strong preference among Americans
for moving in private vehicles is shown by data from the 1995 Nationwide
Personal Transportation Survey. Over 90
percent of all work trips were in private vehicles, vs. 3.7 percent on public
transit. (Since a large fraction of all
public transit work trips are in New York City, if that city’s trips are
removed, only about 2.2 percent of commuters outside New York City use public
transit.) Counting all types of trips,
86.1 percent were in private vehicles, and only 1.8 percent on public transit.
Transit advocates have pointed out
that transit usage has recently grown faster in percentage terms than miles
driven in private vehicles. Therefore,
in December 2000, the Surface Transportation Policy Project (STPP) claimed that,
“Growth in public transit exceeds growth in driving.” But transit usage is so tiny
compared to driving that even very small percentage gains in highway travel
involve vastly larger absolute increases miles traveled than much larger
percentage gains in transit travel.
In 1999, the year about which STPP said that, “Growth in public
transit exceeds growth in driving,” total transit travel grew
by about 1.7 billion passenger miles.
But car passenger travel grew at least 51 billion miles, and travel in
all small private vehicles (excluding motorcycles and buses) increased at least
80 billion miles. Thus, the annual increases
in highway passenger miles traveled in 1999 exceeded those in transit passenger
miles by ratios of either 31 or 48 to 1.
That hardly indicates that growth in transit was exceeding growth in
driving!
More Spending Is
Needed for Public Transit Too -- But Much of It Should Be for a Different Kind
of Transit
The nation’s public transit systems
also need major future investments, but they should aim at making significant
changes in the way public transit is provided.
Future public transit expansion should focus on smaller-scale, more
flexible, and less heavily regulated means of movement that are feasible for
serving relatively low-density settlement patterns, which will remain
dominant. Improving such forms of
public transit will be vital in serving portions of the population unable to
drive, especially the rapidly rising very elderly population. Major spending on fixed-rail systems,
including light rail, is not likely to be very efficient at meeting our most
pressing public transit needs. Moreover,
expanding public transit is also not likely to reduce future traffic congestion
much, if any. Some of the regions with
very extensive public transit systems also have among the most intensive
traffic congestion, including Washington, Boston, St. Louis, and San Francisco.
How Could Future
Traffic Congestion Be Reduced?
What devices exist for improving
future congestion levels -- even though some worsening of congestion probably
cannot be prevented? There are no total
remedies, and not even many approaches that might slow down increases in future
congestion. However, the following
tactics seem the most promising:
--- Coping with Accidents and Incidents
as Causes of Congestion Delays.
Many experts -- including the
TTI -- believe accidents and incidents are the single most important cause of
traffic congestion. Accident rates per
100 million miles driven have been steadily declining, partly because a higher
fraction of traffic is occurring on better-designed roads, especially
interstate highways. But the absolute
number of accidents has stabilized because of increased driving. Probably the most effective way of reducing
accident-caused congestion on major roadways consists of faster removal of
accidents from traffic lanes using roving teams of specialists controlled by
traffic management centers. Many
states already have created such centers, but their effectiveness could be
improved with more sensors and more roving teams of obstacle removing
specialists. This requires intensive
coordination of police, fire, health-care, towing, and communications agencies
in each jurisdiction.
C
Shifting Some Future Growth to Smaller Regions. Multiple regressions based on TTI congestion
measures show that congestion is most serious in the largest metropolitan
areas, and those experiencing absolutely large amounts of population
growth. Smaller areas are not as
seriously affected by congestion even if they have high percentage growth
rates. Hence one long-range offset to
congestion would be shifting more population growth to smaller metropolitan
areas. True, that is difficult to do
through public policies. Most larger
areas want to keep on growing, and they have important advantages of scale to
attract future development. Yet any
individual or organization extremely frustrated by congestion can greatly
improve his, her, or its mobility by moving to a much smaller metropolitan
area.
--- Using HOT Lanes to Provide Drivers on
Congested Roads with a Fast Choice.
On already-heavily-congested expressways, HOT lanes (High-Occupancy-Toll
lanes) can offer a high-speed peak-hour mobility alternative to those drivers
willing to pay tolls, without forcing all those not willing to pay tolls to
drive at other times. HOT lanes accept
both High Occupancy Vehicles (HOVs) and Single Occupancy Vehicles (SOVs) if the
latter pay a toll during peak hours.
The toll is variable, and it is set high enough to keep traffic on such
lanes low enough to permit rapid traffic flow.
This arrangement does not eliminate all congestion on such roads, but
offers drivers a choice of rapid movement through paying high tolls or
congested movement without tolls. Hence
HOT lanes are politically superior to putting tolls on all the lanes in the
roadway, which eliminates the choice of traveling without tolls on that roadway
during peak hours. However, HOT lanes
should be created only by adding new lanes to the roadway or converting HOV
lanes, not by converting existing non-toll lanes to HOT lane use.
--- Metering Access to Expressways. Metering entry-points onto expressways so as
to slow entering flows appears to have some potential for increasing the
average speed during peak hours, according to experience in Seattle. However, it may shift some previous
congestion to lines of people waiting to get onto the expressways through the
meters.
--- Adding Capacity at Specific
Bottlenecks. Where traffic
flows suffer from definite bottlenecks, expanding the capacity of those
bottlenecks might speed flows over the whole network of which they are a
part. However, doing this is often
difficult technically, and may be controversial as well. An example of both problems is the major
traffic bottleneck created by the San Francisco Bay Bridge.
--- Moving Home and Job Closer Together. One tactic an individual can use to cut
commuting time is moving either home or job so they are closer together. This can be quite effective for one person,
but may be difficult for a household in which more than one person works
outside the home. It is also difficult
in regions with very high housing costs, such as the San Jose and San Francisco
areas.
Get Used to Traffic
Congestion
No matter what public policies are adopted in
response to future traffic congestion, it is likely to get worse in nearly all
parts of the world. So my final advice
is: Get accustomed to it. Commute in an air-conditioned car with a
stereo radio, a tape deck and CD player, a hands-free telephone, a micro-wave
oven, and a fellow passenger whose company you enjoy. Realize that congestion is providing benefits to you by rationing
the roads you use and letting you pursue other goals besides rapid
movement. In short, learn to treat
being stuck in traffic as part of your normal leisure life, because it’s here
to stay.
REFERENCES
1. David Schrank and Tim Lomax, The 2001
Urban Mobility Report (Texas Transportation Institute, May 2001).
2. Federal Highway Administration, Our
Nation’s Travel: 1995 Nationwide Personal Transportation Survey, Early Results
Report (Washington D.C.:
Federal Highway Administration, September 1997).
3. Anthony Downs, Stuck in Traffic (Washington D.C.: The Brookings Institution and the Lincoln Institute of Land
Policy, 1992).
4. Bureau of the Census, Statistical
Abstract of the United States: 2000 (Washington D.C: Government Printing Office, 2001). Data on population and vehicle
registrations.
5. Applied Research and Development Facilities
and Activities, part of Cal Poly Foundation, Evaluating
the Operation Impacts of a Variable-Toll Express Lane Facility in the SR91
Corridor , http://airship.ardfa.calpoly.edu/sr91/sr91main.htm. An in-depth study of the longest-established
HOT lanes project in America.
6. Alan E. Pisarski, Commuting In America
II (Lansdowne, Virginia: Eno Transportation Foundation, Inc., 1996).