As such, this issue has joined a whole set of other transportation belief items such as bike lanes versus cars or cars versus transit. Exhibits are Toronto's mayor and his fight against bike-lanes, the current debates about streetcars, the acrimony in the congressional debates about Amtrak budgeting or the refusal of Florida's governor to accept federal high speed rail funding. A current example is Maryland's gubernatorial campaign where the Republican contender announced he will scrap two multi-billion dollar transit projects after over ten years of planning and design.
However, the topic of one-way versus two-way streets is hardly suited for ideological positions even if one approaches the question with "complete streets" in mind and a braoder approach than simply what is best for the automobile, A closer look at the topic reveals that it is less than obvious what is better for pedestrians, bicyclists, transit and residents, ostensibly the other components in a "complete streets" discussion.
To get to the bottom of the debate, it is necessary to recapitulate the reasons that one-way streets were adopted in the first place. The term didn't exist before there were cars in reasonable numbers, even though congestion certainly predates automobiles and goes back to the days of horse and buggy.
These advantages are widely understood and known and are the key reasons why one way streets were introduced in the first place and why they are seen as bad today. Today's logic is often just as simple: what was done in the name of the automobile and its flow must be bad for pedestrians and everybody else not in a car. The instances where the car centric planning of the last 50 years or so has turned streets into inhospitable traffic sewers that are difficult to negotiate for all other modes and terrible to live on are so numerous that anybody simply promoting the inverse, the de-throning of the car in planning, has a receptive audience. From there it isn't far to the logic that what is bad for the car must be good for all other modes. But as we will see, that is a false logic.
The one way issue represents itself in a different light depending if we talk about historic cities that were laid out before cars and have narrow cart-ways or the wide streets of western cities like Denver or San Diego. The initial applications of the one way craze that swept across cities in the US and Europe starting as early as the thirties and carried on well into the 1960s and was eventually applied whether streets were tight or amply wide. Today one should approach the question in a much more comprehensive manner with criteria expanding far beyond traffic capacity and flow of motor vehicles and include at least the following:
- Quality of life of residents along the streets in terms of noise, fumes, safety, access, parking, walking to and from the front door etc.
- Safety, accommodation, convenience and pleasurable experience of active modes such as walking and biking
- Accommodation and operation of transit, buses, streetcars, light rail including stops and stations
- Environmental costs and benefits in terms of noise, pollution, encouragement of active modes versus driving, direct access versus detours
- Urban design. In which way is the city and street better experienced? In which configuration does the street become a good public space or urban room?
Conflict points at two- way intersection
Baltimore has plenty of those narrow historic streets that are just wide enough for two decent sidewalks (partly taken by the famous stoops), a parking lane on each side and two narrow at most 10' travel lanes. Interestingly the city is almost like a large scale test tube for both approaches in dealing with the narrow streets, one way streets and two way streets. North, south and west of downtown and in downtown itself, Henry Barnes, the Robert Moses of Baltimore, has laid out a full system of one way streets. By contrast, the citizens of Fells Point, east of downtown, who had successfully fought an urban expressway, miraculously escaped the craze and have a network of lovely narrow historic two way streets that would make Jane Jacobs smile. Similarly Pigtown (Washington Village) is pretty free of one way streets. Some other urban village areas have hybrids of a mix of one and two way streets in place, such as Hamden and Highlandtown, both with very successful "main street" type streets in two-way configuration.
|Tracing vehicle movement at an intersection in the snow|
Folks north of downtown who live in historic Mount Vernon around the nation's oldest Washington monument, started to question the wisdom of their one-way streets some time ago and even got the transit agency to remove some bus lines from the narrower streets in anticipation of two way traffic which would have made it hard to run the buses. This is an initial example which shows that two way streets in narrow roadways may have unintended consequences. Buses that may work on a 10' lane if no one comes the other way do not run as well if a bus or truck may come the other way.
If the main goal is to slow traffic, two way streets with intersecting two way streets, signalized or as four way stops or signals will do that simply through the creation of many additional conflict points, especially through vehicles that want to turn left. If there is no room for a turn lane they will block everybody behind them, significantly reducing the capacity in a green phase. Seen per street the green phase through-put with one lane in each direction is only half of what it is for a one way configuration if one looks in the direction that was open before. This would be most noticeable in a very directional peak hour flow and less so in a less directional pattern. Of course, it makes little sense to look in only one direction or at only one street if the conversion would occur on several streets, the most likely scenario since one way systems require at least pairs of two streets to work at all. Analyzing one or several pairs of streets, the lane losses on one street are numerically
|windshield perspective of typical Mt Vernon Street in|
Baltimore: St Paul Street
(photo: Gerald Neily)
Overall, in a conversion of one-way into two-way streets a reduction in throughput and speed is to be expected even if the total number of lanes per direction remains the same in any given area. Again, if that is the main goal, the conversion works. However, volume reduction usually is desired to help accomplish other objectives such as improvement of the quality of life for residents along a street or improved safety. Slower cars are certainly good for pedestrians or bicyclists since survival in a crash decreases exponentially with speed. However, the increased safety from that may be more than offset by higher risks at intersections where pedestrians have to fight cars that can come from all directions. Midblock crossing, usually denounced as "J walking" but frequent nevertheless, becomes more challenging when vehicles approach from both directions. Which system really provides the increased safety for walking and bicycling is therefore not obvious and requires a very detailed review.
If bike-lanes are included into the comparison the situation of overall width becomes crucial. If lane width is excessive and can be reduced, bike lanes could be eked out even in a two way conversion. However, in our Baltimore examples with 10' travel lanes, bikes have to share lanes. In the one way model with two lanes in the same direction motorists may change the lane to pass a bicyclist safely. The department of transportation could even become as "radical" as converting one lane of traffic into a protected one-way or two way bike-lane. In the two-way model, i.e. one lane per direction, motorists may have to stay behind bicyclists for entire blocks without a possibility for safe passage, something hard to imagine in the hasty reality of most cities. Cars breathing down one's neck make bike riding also very uncomfortable. A marked bicycle lane, even an unprotected one, is not an option in the two-way model except if a parking lane would be sacrificed. This, in turn is usually unacceptable for residents that rely on those lanes to place their car with off street parking a rarity in the older sections of town.
So far we have only discussed measurable engineering issues such as capacity, conflict points and accommodation of various modes but the matter became complex enough. The issues of noise and pollution track the metrics of flow in some way and are also measurable. The more queuing, stopping and starting, the more pollution. On the other side, if traffic volumes drop significantly, fewer motor vehicles create also less pollution which could offset the increases from stop and go. Lower speeds mean less noise but free flow usually is quieter than stop and go, so here again, benefits and losses accrue on both sides of the ledger.
The urban design and quality of life issues are less quantifiable. For example, Charles Street is Baltimore's eminent north south spine and the divider between the city quadrants. Charles Street traverses Washington Square, one of the most beautiful urban spaces in the country. As such the street has a lot of meaning and is a defining element of Baltimore's identity. Should such a street be experienced from both directions, not only by pedestrians, but also those in buses, cars or on bicycles? Isn't the square designed this way with its split road-bed around the monument? In many ways the answer would be yes, a reason why the request for a two-way Charles Street has come up many times.
|Washington Square in Mt Vernon, Baltimore|
One way north on both sides.
The question remains, should the status of even our premier streets be decided by engineers on the basis of the rather dense "science" of traffic engineering which leaves everything else unanswered? Shouldn't vital issues like this be a civic decision based on a much broader set of value questions ranging from urban design to business? Who responds to the concerns of retail and restaurants on those streets where speed, throughput and restricted parking translate into life or death for a business and are often valued differently by traffic engineers.
The situation is quite different in many western cities where cart-ways are typically much wider and one way streets were not put in place for lack of space between the curbs but solely for traffic management and signal control reasons. Denver or San Diego have many super wide downtown streets that are one way with six or even more lanes all in one direction where diversion into two way traffic would pose few space problems and still leave space for bike lanes, medians and the like.
Getting this far the reader may be thoroughly confused and we haven't even mentioned specialty solutions such as rush hour only one-way streets employed by a few cities in an attempt to bridge the best of both worlds. There is no way around it: there is no simple answer. The topic of one-way versus two-way streets is ill suited for ideological disputes or culture wars. What is best for a city, community or neighborhood needs to be carefully weighed using as many metrics as possible. The answers will vary from case to case.
Still, one can probably safely conclude that one-way streets, having been imposed on cities across the world without much deliberation and only with the consideration of throughput efficiency in mind, won't always hold up to a more comprehensive evaluation two-way streets may often be better, indeed. Either way, a street needs to be so much more than just a conduit for motor vehicles.
Klaus Philipsen, FAIA
edited by Ben Groff
Related articles on this blog:
Complete Streets, the DNA of a New Mobility Culture
Traffic Management: The End of the Tyranny of the Red Light?
The Street as a Public Space: Rethinking Public Spaces
Mode Choices: A City for People and Not For Cars
External sources and links:
A pamphlet against one way street conversion