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Thread: One way vs two way streets

  1. #1

    One way vs two way streets

    Our City is contemplating a new traffic pattern. Here is the setup: We have two parallel five lane (two + center turn + two) arterials one carrying about 25,000 ADT and the other about 15,000 ADT. The each serve a major employer on the edge of town, so we have large am and pm peaks. The two arterials are split by our downtown area that contains a minor street down the middle. One arterial is bordered by small lot single-family residential, and the other arterial is bordered by a riverfront park system.

    We are contemplating a one-way couplet concept, and have a transportation consultant studying the idea. We recognize all of the downfalls of traditional one-way streets in pedestrian downtown areas, such as choices between auto mobility at the expense of pedestrian mobility. Here is where we are going to try something different.

    We are going to narrow the arterials from five lanes to three. We think we can do this without sacrificing capacity, and at the same time we can widen sidewalks, increase landscaping/street trees, streetscaping, on-street parking, loading zones, curb bulb outs, etc...

    In short, we think there are some important urban design features we can accomplish through this action. The question is this: are those features enough of a benefit to warrant a switch to a one-way couplet concept?

  2. #2
    Urban Design by itself is nice, but it has to accomplish certain aims. If your aim is to make the streets pretty and nothing more, fine. But my point is that "urban design" by itself. You have to prioritize what you want to accomplish. There is absolutely no way that you can manage such a radical reworking without some negative aspects. You have to prioritize what is most/less important to your city. You can add landscaping, but if the going-home traffic is routed on the street with no retail-grocery stores etc. than your "landscaping" will have had an overwhelmingly negative effect on the city. The information given is not enough to really say very much, but I would stress that "making a street nicer" is NEVER a good enough reason in itself.

  3. #3
    Dear WA Planner,

    It seems that you have considered some important points about the risks of converting from two-way to one-way traffic flows. But you may have missed out one important aspect. Businesses!

    While a one-way arterial will carry significantly more traffic you may find that businesses located along the arterial will begin to see less and less customers. This effect has been widely studied and is due to the fact that one-way streets increase speed and make it more difficult for shoppers to see what's around them. Yes, you have thought about increasing the size of sidewalks, but do your customers walk from their homes nearby, or do they drive in from suburbs and/or other neighborhoods. If they drive you'll hurt your businesses.

    Here are some other questions I would ask before moving forward. Will your flow increase so significantly that the investment is worth it? Why do you want traffic to flow faster? Do you want to get people into or out of this neighborhood? Have you considered if drivers really want to move faster? Will the changes be easily reversed if in five years your plan seems to have failed miserably?

    Good luck.

    p.s. I recommend the traffic manual produced by the National Main Street office at the National Trust for Historic Preservation.

  4. #4
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    two-way vs one-way

    I'm interested to see if anyone has done any recent before and after studies of one-way conversions. I have seen reference to a number of studies from the 50s and 60s that all found a significant (around 30%) reduction in collisions with one-way vs. two-way streets.

    I like the idea of taking advantage of the efficiencies offered by one-way streets to provide wider sidewalks, angle parking, bike lanes, bus lanes, etc. We have all of that in San Francisco and I think it works well, although the South of Market Area still has too wide streets (about 60 feet). And we have extra capacity in some of the narrower North of Market Streets (about 44 feet) that has led some advocates to urge us to convert them to two-way, although they are under what I believe to be a mistaken impression that two-way is safer than one-way

  5. #5
    I like the idea if the downtown has a centralized population. Improved access to the waterfront park would also be a possible benefit and possibly a spin to add to the promotion campaign.

  6. #6
    Cyburbian DetroitPlanner's avatar
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    If this is to accomodate one large employer, you should also look at peak hour traffic counts, not just ADTs.

    Using my general guidelines, and thats all I can do without extensively studing your situation you may run into some major congestion problems during peak hour running 3-lane roads. Therefore, you may be actually hurting the company you are trying to help. I would tend to agree that you should also look at all of the other points brought up as depending upon the situation, each may be very valid as well.
    We hope for better things; it will arise from the ashes - Fr Gabriel Richard 1805

  7. #7
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    Nashua, NH
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    It is easier to time the traffic signals for a one way street compared with a two way street, although in a typical city grid system there are still numerous problems.

    If a one way street is to be converted to two way, one possible compromise is having more lanes in the original one way direction and retaining the signal timing originally used for the one way, The other direction becomes a "local service road" for businesses.

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