Vanishing Automobile update #30

Should Cities Convert One-Way Streets to Two Way?

The latest fad among urban planners is to convert one-way streets to two way. The goal, they say, is to slow down traffic and make streets more pedestrian friendly.

One-way to two-way conversions are being planned or implemented in Austin, Berkeley, Cambridge, Chattanooga, Cincinnati, Louisville, Palo Alto, Sacramento, San Jose, Seattle, St. Petersburg, and Tampa, among other cities. These proposals have become a major source of controversy in at least some of these cities, especially Austin, Cincinnati, and Chattanooga.

By almost any measurable criteria -- safety, pollution, congestion, and effects on most local businesses -- one-way streets are superior to two way. The idea that two-way streets are superior because they are more pedestrian friendly is just a planner's fantasy that disguises their real intent: to create an auto-hostile environment.

The History of One-Way Streets

Most one-way streets in this country were first created from two-way streets in the 1930s through the 1950s. These conversions took place in areas built before the automobile became the prevalent form of transportation. Such areas tend to have narrower streets and smaller blocks than post-auto cities. One-way streets were thus an attempt to accommodate auto traffic in areas not built for the auto. The wider streets and longer blocks typical of post-auto areas often allow improved traffic flows without one-way streets.

Before the 1990s, transportation policy was firmly in the hands of traffic engineers, whose primary goal was safety and secondary goal was the movement of people and goods. Cities that converted two-way to one-way noted a significant decline in accidents.

One-way streets have the obvious advantage that pedestrians and drivers need only look one way when watching for traffic. How many times have you looked both ways when crossing a two-way street, only to be nearly hit by a car coming from the direction in which you weren't looking at the moment you entered the intersection?

One-way streets also permitted higher average speeds because signals on a one-way grid could be synchronized to allow drivers in all directions to proceed indefinitely at a fixed rate of speed. A semblance of synchronization can be approached on a two-way grid only if signals are more than a half-mile apart, and even then it is less than perfect. Traffic on two-way streets, for example, is often delayed by special left-turn signals, which aren't needed on one-way grids.

Faster speeds on signal-synchronized one-way streets increased road capacities without laying more pavement. Since the increase was in the average rate of speed, not the top speed, increased speeds posed no loss in safety. One way streets not only have greater capacity than two-way streets, they save the space that two-way streets require for left-turn lanes.

In the 1970s, a new goal -- reduced air pollution -- led to more conversions of two-way streets to one way. The smooth flow of traffic allowed by signal synchronization meant less auto emissions. Since cars pollute more at slower speeds and in stop-and-go traffic, one-way streets can generate significantly less pollution than two-way.

Proposals to Convert Back to Two Way

Today, transportation policy is in the hands of urban planners who claim their goal is to make cities more livable by designing them for people, not cars. The fact that people in most American cities do 85 to 95 percent of their travel by car does not deter planners from making this artificial dichotomy.

"A pedestrian-oriented hierarchy of transportation promotes density, safety, economic viability, and sustainability," says Austin's Downtown Design Guidelines. In transportation planning, "sustainable" has become a code word for "anything but automobiles." Beyond this, Austin does not say why density is an appropriate goal, nor have planners shown how a pedestrian orientation is more economically viable than an auto orientation.

Austin goes on to say, "The safety and comfort of pedestrians is of greater concern than the convenience of a driver." This statement assumes that pedestrian safety and comfort is incompatible with the convenience of drivers. In fact, there is no reason why this must be so.

Planners only sometimes admit that their real goal is to discourage driving by creating auto-hostile environments. Since every single car on the road has at least one person in it who is trying to get somewhere, this is hardly a people-friendly attitude. More important, in their single-minded opposition to the auto, planners have forgotten about safety, environmental, and social concerns.

Two Kinds of One-Way Streets

The controversy over converting streets back to two way involves two different kinds of one-way streets. First is the downtown grid, which typically has traffic signals at every intersection that are set for speeds of 15 to 20 miles per hour. Second is the one-way couplet, two streets that feed traffic into downtowns or other busy areas. These typically have traffic signals only at major intersections which, if they are synchronized, are typically set for speeds of 25 to 40 miles per hour.

Conversion of part of a downtown grid to two way means a significant loss of both safety and traffic flow. Other than the psychic benefit some people get when they see other people stuck in traffic, such conversions have no positive results. In fact, they are likely to contribute to downtown decay as they reduce the capacity of streets to carry traffic into and through downtowns.

Converting one-way couplets to two way could reduce flow capacities by nearly half. "You need seven lanes of a two-way arterial to achieve the same capacity as four lanes of a one-way couplet," says transportation planning Michael Cunneen. However, planners usually want to reduce traffic flows by even more than this amount. Their proposals often call for: * Reducing the number of lanes of auto traffic; * Narrowing lane widths; * Removing right- and/or left-turn lanes; * Adding median strips or other barriers to streets: and * Other traffic-calming (i.e., congestion-building) actions.

In Chattanooga, for example, McCallie and ML King avenues form a one-way couplet of four broad lanes in each direction. The city plans to convert both to two way. ML King would have two lanes in each direction, but McCallie would be reduced to one lane in each direction plus an intermittent left-turn lane. The two lost lanes would be turned to on-street parking. The result would be a net loss of two lanes, and the remaining lanes would be slower (meaning lower in capacity) than the current lanes. Planners say these steps will make streets more pedestrian friendly and that the resulting reduction in speeds will make up for the reduced safety of two-way streets. However, planners' real goal is to reduce roadway capacities.

Planners in Chattanooga and certain other cities, such as St. Petersburg, argue that the decline of downtown areas since streets were converted to one way has reduced the need for roadway capacity, so the reduction in capacity is not a problem. However, limited capacity would inhibit the downtown revitalization that planners say is also their goal.

Economic Vitality

Planners assert, with little or no evidence, that two-way streets will revitalize downtowns and other areas. One-way streets supposedly hurt businesses by forcing some people to drive around a block to get to those businesses. Yet the higher average speeds of one-way streets (due to signal synchronization) reduces the total time it takes people to get to any destination even if they sometimes have to drive around a block.

Planners also argue that one-way streets have higher top speeds than two-way streets, and that a lower top speed makes it more likely that drivers will see and stop at businesses along the way. But the top speed of a street is independent of whether it is one way or two way. What planners mean is that when they convert to two way they also plan to reduce top speeds.

"One-way streets are a 1970s traffic engineer's approach to getting traffic out of downtown," says Donald A. Shea, who represents a downtown St. Petersburg advocacy group. "Well, it worked. And some of it has never come back."

Shea is confused. One-way streets allow more traffic into as well as out of downtown. Businesses that left downtowns for the suburbs did so in part because downtowns were more congested than the suburbs. To the extent that one-way streets reduced congestion, they mitigated, rather than contributed to, downtown decline. Of course, downtowns declined for many reasons other than congestion, but there is no reason to suspect that converting one-way to two-way streets will reverse this decline.

This does not mean that no businesses would benefit from a conversion to two-way streets. Certainly many businesses complained that converting two-way to one-way in the 1950s led to a loss in revenues. The truth is that some businesses probably do better on a two-way street while others thrive on a one-way couplet.

Supermarkets and other high-volume, low-margin stores that have their own parking lots (most of which are dominated by one-way lanes) probably do better on a one-way couplet that gives lots of people quick access to those stores. Specialty stores that rely on impulse sales and depend on high margins per sale might do better on two-way streets, since only half their potential customers would see them on a one-way couplet.

Some people argue that such considerations are purely private and not the business of government. "The primary purpose of roads is to move traffic safely and efficiently, not to encourage or discourage business or build or rebuild parts of town," argues engineering Professor Joseph Dumas, of the University of Tennessee at Chattanooga. "Streets are tools for traffic engineering, not social engineering."

Dumas might say that a business that does best on a two-way street should locate on a two-way street. Many planners, of course, would disagree and claim that it is the business of government to promote business. However, there is no evidence that two-way streets and reduced traffic flows will do so.

Past efforts to promote pedestrian-oriented downtowns often involved complete exclusion of automobiles from certain streets. Such pedestrian malls have occasionally been successful, such as Pearl Street in Boulder. But more often they have led to the death of businesses on the mall.

Eugene, Oregon, turned three major downtown streets into a pedestrian mall in 1971. Local businesses noted an immediate drop in sales, and Sears, Penneys, Wards, and other stores soon pulled out. Yet it took two decades for city planners to give up and re-open the streets to auto traffic. One street was opened in 1992, another in 1996.

In 2001, two out of three Eugene voters supported a plan to open up the last street of the pedestrian mall to autos. Downtown business leaders called this "the critical first step in revitalizing" downtown.

Turning one-way streets to two way and other congestion-building measures are not as auto hostile as completely closing streets to autos -- but they have the same anti-auto aim. There is no reason to think that reducing roadway capacities will revitalize downtowns any better than eliminating roadway capacities.


The evidence that two-way streets are more dangerous than one way is overwhelming. In many cases, two-way streets result in twice as many pedestrian accidents as one way.

One review of two-way to one-way conversions found that two-way streets caused 163 percent more pedestrian accidents in Sacramento, and 100 percent more pedestrian accidents in Portland OR, Hollywood FL, and Raleigh NC. This study called one-way streets "the most effective urban counter-measure" to pedestrian accidents.

One-way streets also lead to fewer motor vehicle collisions. While the reduction in collisions is not as great as the reduction in pedestrian accidents, Michael Cunneen says, "two-way streets are designed more for auto body shops than for people or cars."

Since most conversions of two-way to one-way streets were done in the 1950s, few studies are available on the internet. The above-cited study is from 1976, and is titled "National Highway Safety Needs Study," published by the Research Triangle Institute for the US Department of Transportation.

The claim that slowing traffic will reduce the safety problems of two-way streets is diminished by the fact that congested streets with narrow lanes will also slow emergency service vehicles. As pointed out in "The Vanishing Automobile," studies of traffic calming show that delays to emergency service vehicles will kill far more people than will be saved by the slower speeds (p. 352).

Transportation consultant Michael Cunneen is currently doing a literature review on the safety of one-way vs. two-way streets which will be published as a future Vanishing Automobile update.


Cars pollute more at lower speeds than at higher speeds. They also pollute more when they accelerate than when they travel at a constant speed. Thus, the stop-and-go traffic that is more likely on two-way streets than one way, as well as the slowdowns planners seek by narrowing lanes, both lead to increased air pollution.

In fact, when Congress first required cities to reduce air pollution in the 1970s, many cities responded by improving signal synchronization and speeding up traffic downtown. Faster speeds meant less congestion and lower emissions. Since downtowns were the location of the most concentrated pollutants, such lower emissions could make the difference between pollution violations and compliance with federal pollution laws. Even today, signal synchronization is the most cost-effective thing most cities can do to improve air quality.

Most planners today ignore this side-effect of their pedestrian fantasies. But planners in Austin took the trouble to calculate that converting several one-way streets to two way would increase traffic delays by 23 percent and increase downtown air pollution by 10 to 13 percent. That's a huge increase in pollution for a policy with such questionable benefits -- especially since air pollution is the main legal justification planners have for trying to reduce the amount of driving we do.


Increased auto ownership and driving is largely a function of income. As incomes rise, more people buy cars. Auto ownership gives low-income people access to more jobs, especially considering that commuter auto speeds remain more than double commuter transit speeds. Autos also provide better access to low-cost consumer goods and services.

Low-income people tend to remain concentrated in the inner cities where planners most often propose to convert one-way to two-way streets. The loss of mobility imposed by these conversions will fall most heavily on such low-income people. Higher income people are more likely to live and work in the post-auto suburbs where one-way streets are rare because they weren't needed to accommodate auto traffic.

Gainesville, Florida, is considering a plan to reduce its major east-west thoroughfare from four lanes to two lanes. Since most of the city's low-income people live on the east side and most of the jobs are on the west side, this action will severely reduce low-income access to jobs. Proposals to reduce speeds when converting one-way to two-way streets in other cities will similarly harm low-income people.


Converting one-way to two-way streets is "a huge waste of money," says Fabian Bandoni, Cambridge's former director of engineering. St. Petersburg, for example, estimates that it will cost nearly $150,000 to convert each major intersection that is changed from one way to two way. Converting an entire one-way couplet or a portion of a downtown grid may run into the tens of millions of dollars.

The debate over one way to two way has led many traffic engineers to publicly object to these plans. In Cambridge, Chattanooga, and other cities, traffic engineers have become outspoken opponents of one-way to two-way conversions.

Planners probably consider traffic engineering goals of safety, traffic flows, and reduction in pollution to be archaic. But the cost issue may sway many city councils, especially considering the current recession.


On just about any ground imaginable -- safety, congestion, pollution, and effects on most businesses -- one-way grids and one-way couplets are a superior method of moving people and vehicles. The idea that pedestrian-friendly design can be enhanced by creating more pedestrian-deadly environments is just a planning fantasy.

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