Converting One-way Streets to Two-way
Managing Traffic on Main Street
By John D. Edwards | From Main Street Story of the Week | June 2002 | 187
There has been a resurgence of interest in downtown redevelopment in the past two decades. Whether this is the result of programs such as Main Street or simply a renewed interest in downtown from "baby boomers" and municipalities that now recognize the importance of the downtown tax base, it is happening. Along with this "broader" interest in traditional commercial districts, we see more concern and interest in the ‘nuts and bolts' of what makes a downtown actually work better. One of those nuts and bolts is the downtown street system.
In the 1960s and ‘70s, the primary traffic issue for downtowns was how to reduce "congestion" and make traffic move faster, i.e., provide maximum mobility. In the late ‘80s and '90s, there was a realization that maybe some traffic congestion downtown is good. Maybe we don't have to "give over" the entire commercial district to the automobile and make all systems subservient to vehicular mobility. As a result of the resurgence of central business districts and the need to slow traffic to make the area more pedestrian friendly, we have begun to look at those operational techniques that cause high-volume and high-speed traffic. One-way traffic is one of those systems that has come under recent scrutiny.
Why One Way?
How did one-way streets become so popular downtown anyway? There were several problems that led to commercial districts adopting one-way traffic systems:
> Needed increases in capacity;
> Preservation of on-street parking;
> Increasing traffic; and
> The lack of by-pass facilities for through traffic (motorists who didn't want to drive through downtown anyway).
Increases in capacity were needed during the 1950s and ‘60s because of dramatic increases in travel. As a result, there was a tendency to remove on-street parking to make more travel lanes, thereby giving preference to mobility. By switching to one-way traffic, it was possible to preserve on-street parking in many districts while increasing the traffic-carrying capacity of the existing street network.
In the 1960s and 70s, traffic continued to increase on main street because of the growth of urbanized areas, although retail growth in central business districts (CBD) had begun to decline. By the 1980s, not only had retail growth declined but other downtown land uses were relocating as well. Finally, the construction of many bypass facilities both as a part of, and in addition to, the growth of the interstate highway system, put a virtual stop to traffic growth in most CBDs; and many downtowns experienced actual declines in traffic volume on some of their streets.
Given this history, why even be concerned about converting one-way streets?
Making Main Street "Customer Friendly"
Many factors combine to make main street economically successful. One important, but often overlooked, aspect is the traffic pattern. One-way streets are efficient but they are not customer friendly for people coming downtown to shop two or three times a month. For these infrequent visitors, the downtown circulation system needs to be as easy to use and as easy to understand as possible.
A major concern of organizations working to revitalize traditional commercial districts is to improve retail sales, and, more specifically, to boost the visibility and accessibility of the retail segment of the district's complement of government, services, and retail. In this regard, making the circulation system more "customer friendly" is a prerequisite to increasing the retail segment of downtown and appealing to investors and merchants who are interested in coming back to main street.
Retailers aren't the only businesses dependent on easy-to-understand traffic operations, however. Service operations and professional offices also need a circulation system that is easy to understand and to navigate; and in most small to medium-sized communities (10,000 to 50,000 in population), two-way streets are preferable.
One-way streets increase travel. Because most one-way systems do not allow motorists to travel directly to every destination, there are some locations that one must drive past, turn around, and then drive back in order to gain access. So in any downtown grid, there will be "dead blocks" -- meaning from an access standpoint, they require circuitous routing to arrive at a destination located in that block. (see Figure 1)
Another perception that affects the success of downtown retailing is "does it feel exciting, are there lots of people?"which means a certain degree of congestion. One-way circulation is so efficient at moving traffic that the streets may feel empty! Thus a commercial district needs to have a certain level of traffic congestion so that it appears busy.
How fast cars travel on downtown streets is another issue. Any successful main street district will have considerable pedestrian traffic, and where pedestrians are present, operating speeds should be low -- 15 to 20 miles per hour. One-way streets, especially one-way road pairs of 10 to 15 blocks in length, tend to encourage higher operating speeds, usually in the range of 35 to 40 mph.
When should a community consider converting a street or network of streets from one-way to two-way traffic? The most important consideration is whether it will help the revitalization effort. If the area affected by the conversion is a retail district that is experiencing a comeback, then a conversion may be warranted. If, however, the area adjacent to the one-way street is primarily office, warehousing, or industrial, with high peak-hour traffic, then a conversion may not be worth it.
Perhaps the most important reason for changing the traffic flow of a downtown street is to improve the economic well-being of the commercial district. A survey of 25 towns and cities that have converted their main streets show that many have experienced significant reductions in vacant floor space after the conversion. (See Table 1.)
All of the communities surveyed reported positive results after converting their one-way streets to two-way traffic, and many reported substantial private investments stimulated by conversions that were coupled with streetscape projects. West Palm Beach, for example, reported $300 million in private investment in areas where city hall had invested $10 million in public funding.
Changing the downtown environment so that it better serves pedestrians is another major reason for converting one-way streets. In several communities, operating speeds were reduced from 30 to 45 mph to 20 to 25 mph. Slowing traffic has the advantage of reducing noise, water and snow splash, and fumes -- all problems for people walking on the sidewalk.
An even more important benefit is the increase in pedestrian safety. In the booklet, MAIN STREET-When a Highway Runs Through It, published by the Washington State Department of Transportation, speed is related to driver perception and the severity of injuries at various speeds. For instance, at 40 mph, the driver's focus is on the roadway at a distance; at 30 mph, the driver begins to see things at the road's edges; and at 20 mph, the foreground comes into focus. At 15 mph, the motorist sees pedestrians and other elements on adjacent buildings. The booklet also points out the chances of fatality to a pedestrian who is struck at various speeds: at 40 mph, the chance of death is 85%; at 30 mph, it is 45%, while at 20 mph, the chance of a fatal injury is 15%.
Another factor to consider is the type of traffic flow. If it is mostly throughway traffic with few people stopping at downtown destinations, then the conversion may have little or no impact on revitalization of district.
Along with type of traffic is the amount of traffic. If traffic volumes exceed 15,000 vehicles per day (vpd) on each of the one-way streets and if there are numerous cross streets with no suitable parallel or bypass routes, the conversion to two-way may increase congestion to unacceptable levels and actually deter shoppers.
A final consideration is street width, and its impact on on-street parking and off-street parking access/egress. If streets are narrow, there may be a significant loss of parking. Streets less than 22 feet wide are not good candidates for two-way operations; left-turn movements will cause congestion. For off-street parking lots and garages, the access design of the entrance/exit may require substantial reconstruction to accommodate a change to two-way operation. Another potential expense to consider is the cost of changing traffic signals and signs to accommodate the conversion. These changes can be expensive, especially if electrical wires are underground. In Greensboro, N.C., for example, the estimate to convert one street was $30,000 per intersection.
What You Need to Know
What information do you need to determine the desirability of a street conversion and where do you get it? The types and level of analysis depend on a variety of factors, including:
> the jurisdiction under which the street(s) operate;
> street widths;
> amount of daily and peak-hour traffic;
> adjacent building use;
> pedestrian activity;
> level of congestion;
> possible economic impacts; and
> how the facilities relate to the local and regional transportation network.
Street jurisdiction refers to the legal authority under which the street operates. Is it a federal, state, or local route? If it is a federal or state route, it will be necessary to get approval to make the conversion and the studies required may be fairly rigorous. If the street is under local jurisdiction, the conversion will be under local control, and the decision may be dependent only on traffic volumes and parking needs. Several streets in Green Bay, Wis., and other small downtowns have been converted to two-way operation with little study or negative impact.
Street Width and Lane Use
Perhaps the most important consideration is street width. Obviously, two-way operation requires a minimum width of 24 feet. If there is parallel parking on both sides of the street, the required width may be 36 to 38 feet; and with angle parking on both sides, the width expands to 64 to 68 feet. These widths do not provide any left-turn lanes, so if there is a heavy amount of left-turn traffic, additional width may be required. Table 2, below, gives minimum curb-to-curb widths for various parking and traffic lane configurations. As you can see, angle parking increases minimum required widths considerably due not only to the depth of the parking aisle but also the maneuvering space required.
Daily and Peak- Hour Traffic
The amount of traffic, both daily and during peak hours, must also be considered. For streets carrying more than 10,000 vehicles per day, make sure that most of the traffic consists of local shoppers; otherwise severe complaints will ensue. Peak-hour volumes of more than 500 vehicles per lane can cause considerable delay due to the new left-turn movements generated by the conversion. If you plan to convert streets with high traffic volumes, look for alternative routes with surplus capacity that can be used by drivers who aren't planning to stop at any of the businesses on the converted streets.
Adjacent Building Use
Building use along the street is another important factor. The basic reason for converting a street to two-way traffic is to make the circulation system easier to understand and use. For people who work or live downtown, this may not be an important issue. For shoppers, it's a different story; two-way streets can help them reach their destinations more quickly and easily. Thus, streets with predominantly retail uses are usually the prime candidates for conversion.
Another significant building use that can affect two-way conversions is the presence of a parking garage or deck. Parking structures specifically designed for one-way operations may require redesign and reconstruction of their entrances and exits to accommodate the new traffic flow. While parking lots may also need modification, changes to surface lots are, in general, much easier to make than alterations to parking structures.
Improving the pedestrian environment on adjacent sidewalks is one of the major reasons for converting one-way streets to two-way operations. This can occur by reducing traffic speeds, noise, rain and snow splash, and vehicular-pedestrian conflicts. To obtain significant benefits through the above actions, there must be either existing or anticipated pedestrian traffic on the sidewalks. If the buildings along the street do not generate significant pedestrian activity, the conversion will generate fewer pedestrian benefits. Areas in which pedestrian traffic volume is less than 200 to 300 people an hour will probably experience minimal benefits. Pedestrian studies that include existing counts of activity on downtown sidewalks can help determine whether a conversion will benefit the district.
Levels of Congestion
Typically, traffic engineers and transportation planners strive for intersection levels of service of "C" or above; which means vehicular delays of 30 seconds or less. Most downtowns, however, must be willing to accept higher levels of service because pedestrians are present and drivers are turning or pulling into or out of parking spaces. The wait at intersections is less important because conditions in the middle of a block may exert more control over vehicular delay than traffic signals. For commercial districts, especially retail areas, levels of service of "D" or "E" are acceptable: this means average waits of up to 60 seconds at intersections. Capacity and level of service analyses are essential studies for any proposed street conversion.
Levels of traffic congestion affect operating speeds as well. From the standpoint of pedestrian safety, vehicular speeds of more than 25 miles per hour for retail streets are undesirable. On-street parking will slow the speed of traffic as well, making it desirable for the retail areas of main street districts.
Conversions and the Regional Transportation Network
One-way to two-way conversions may depend on the way the proposed streets fit within the regional roadway network. When considering a conversion, it is necessary to look at the network and see how a change will affect traffic operations regionally. For instance, if a freeway interchange system is designed to operate with the one-way system in the commercial district, it may not be possible to make a change. On the other hand, if there are parallel routes to which "through" traffic can be diverted, a conversion may be possible. In any event, studies should be conducted to determine how much of the traffic flow is "through" and how much is "local."
Truck traffic is another consideration. Is there a high volume of truck traffic on the streets to be converted? If so, thought must be given to the diversion of truck operations to a parallel route in order to reduce congestion on the proposed two-way street.
The Benefits of Street Conversions
Street conversions to two-way traffic should be based upon real and anticipated economic benefits, such as reduced vacancy rates, increased retail sales and employment, increased pedestrian activity, and/or increased property tax assessments. While a growing number of communities are opting for two-way traffic in their business districts and there is significant anecdotal evidence that positive changes occur after most street conversions, there has been limited research on actual retail sales and property value increases. More economic data is needed to support the economic benefits of these conversions.
John D. Edwards has more than 35 years experience in traffic, planning, and parking. He worked as a transportation planner for the City of Cincinnati, as a project engineer for the North Carolina Department of Transportation, and as a pricipal in consulting firms.