Are Two-Way Streets the Way of the Future?

Today on the Streetsblog Network, we’re featuring a post from San Francisco’s Pedestrianist
about two-way street conversions in Minneapolis and how such changing
traffic patterns could benefit pedestrians and other users:

3291357587_5bdc4ca1a8The city of Minneapolis is about to return two of its downtown streets to two-way traffic
after nearly 30 years of one-way flow. Those streets, like many in
downtowns across the country, were converted to one-way couplets by
auto-centric traffic engineers in the middle of the last century.

Their goal was to squeeze more cars through older, narrow streets
as fast as they could. And that’s exactly what happened. The problem is
that the fast, thick traffic along these one-way streets has proven to
be dangerous to vulnerable road users, especially pedestrians, and has
often pushed away much of the street life.

In San Francisco, the grid of one-way streets on either side of
Market and around the old ramps to the Central Freeway in Hayes Valley
and the Western Addition are among the most dangerous places to walk. The recent killing of a woman on Fell Street has prompted numerous calls to calm the traffic on that and other unidirectional expressways. One of the more common sentiments expressed in comments on Streetsblog is that these one-way couplets should be restored back to two-way traffic.

Two-way streets are naturally calmer because cars approaching from
opposite directions make each other nervous. Nervous drivers are slower
and more alert to their surroundings. Two way streets are also easier
for bicycles to navigate, and the presence of bikes on a street further
calms car traffic.

There is, in my opinion, no reason not to begin restoring two-way
traffic on San Francisco streets, starting with the most dangerous
first. The lives of our neighbors are too high a cost to justify a
slightly faster car commute.

More from around the network: FABB Blog and Missouri Bicycle News call attention to a Parade magazine article about the bicycling mayor of Columbia, Missouri. Greater Greater Washington scrutinizes the National Park Service’s rejection of a request to use Rock Creek Parkway for an organized bike tour event. And Let’s Go Ride a Bike has more on the biking gender gap.

Photo by wvs via Flickr.

  • Hear, hear!! It is time to start undoing the damage done by 1950s traffic engineering, whose only goal was to move cars as quickly as possible, regardless of the effect on safety and on the surrounding neighborhood.

  • Repost my comment from older article. I think this two way street is a fallacy that certainly should not apply to traffic corridor.

    How Signal Synchronization work on an one way street

    1. The diagrams below shows 3 traffic signals. 4 cars are stopped at the first traffic light. The Signal synchronization scheme will turn each traffic light to green in succession in a finely timed manner.

    1. __*_*_**R________R_________R_______

    2. ____*__*G*__*____R_________R_______

    3. ________G__*__*_*G*________R_______

    4. *_______G_______*G*_*_____*R_______

    5. ______*_R________G___*_*_**G_______

    2. The first signal turned green. Cars are moving to the right, heading toward the next red light.

    3. The second light turned green precisely after the time it takes to travel from light 1 to light 2 at 25 mph. The light turn green for the first car just in time. This is the optimal condition when every car travels at 25 mph.

    4. The first car speeds and pull away from the pack. It hit the third light too soon before it turns green. It has to come to a complete stop at the red light.

    5. The third light turns green. The first car have to start from a complete stop, slowing down the entire pack.

    Because of the signal timing, it is optimal for every car travels at precisely 25 mph. At long as there are enough traffic, it is almost impossible for cars to go much faster than 25 mph.

    This scheme is impossible on a two way street. The light cannot be set to turn green at the right time for traffic coming from both direction. Therefore signal timing cannot be used to regulate the traffic speed as in a one way street. Instead, they will probably keep the signal green for a longer period to maintain the traffic flow. This will probably make it easier for speeding. You can see plenty of evidence of this on 19th ave. Now imagine if 19th ave were designed as two separate one way streets with signal synchronization.

  • Dunce

    Actually, Wai, it is possible to regulate traffic speed on a two-way street using traffic signal coordination.

    On Valencia St, the signals are set to regulate traffic at 13 mph, in both directions.

    On Sunset Blvd and the Great Highway, the signals are set to regulate traffic at 30 mph, in both directions.

  • Eddie

    The problem is simply that a pure focus on slowing traffic down actually has a negative effect on the residents of the area as well. San Francisco, in particular, has a substantial percentage of its residents who work outside the city. Increasing the amount of time it takes to get across the city or out of it fundamentally decreases those residents’ quality of life.

    A functional public transit system would ameliorate but not alleviate this problem–but that system doesn’t exist.

  • patrick


    The problem with your analysis is that you are focusing on the car at the front of the pack. It’s true they can’t go any faster than 25, but on the other hand, any car that is far behind the pack is in fact incentivised to speed. If a car is far back enough, if it travels at 25mph it will get stopped by the first light, while if it travels at 40mph it can travel for many blocks until it finally catches up to the pack. This happens every day on Fell & Oak, and Pine & Bush, and a number of other 1-way pairs, and is very dangerous.

  • patrick,
    You are absolutely right. I notice this as well. Buses cant make the the lights because of boardings, and so cars have yet another unfair advantage as well. Id like to see signal prioritization for buses for once, for 19th ave as well as for the N,T,L lines.

  • huh

    @Patrick’s point is the key. While the lights may be timed so the FRONT of the pack can’t go more than 27mph, cars trailing off the back of the pack can drive well over 40mph for many blocks through green lights before catching up. The problem is that the lights on Fell and Oak are kept green for far too long so that cars can do this blocks-long “catch up” thing. Cars on Fell and Oak can even make the leap from one “bunch” to the next because the lights are green for so long. Additionally, many cars on F&O turn onto to those streets mid-way through light cycles are not part of the “pack.” I bet that if one were to actually analyze the speeds of the cars on Fell that one would find that over 75% of them are travelling at speeds well over the “synchrozation design speed” on any one block over the course of a light cycle. The additional, and unmitigable, severe dangerous aspect of light synchronization such as on F&O is that it encourages drivers to try to beat the changing traffic lights and try to “predict” the changing of a red to a green light: cars at the front of the pack don’t slow down on approaching the red lights and so often run the red lights in anticipation that the light should have changed, and cars “catching up” to the pack try to get through the lights changing to red because they have built up a head of steam and are trying to charge on through.
    All in all, F&O are managed like freeways, neighborhood safety be damned.

  • @Dunce, I don’t understand how it can regulate traffic in both direction. Won’t it requires the signal to be consistent for both direction to accommodate cross traffic? How can the light turn successively from both direction?

  • @patrick, signal synchronization is not a cure all solution. It works better when there are fair amount of traffic. But the signal alone cannot prevent speeding under all conditions. Other means of enforcement may still be necessary, just like any other streets.

    But even when a car behind the pack have room to speed, it can only speed for a few blocks before eventually stuck behind other traffic. This is still an improvement over a free flowing freeway where all cars travel at high speed. (e.g. 19th ave)

  • patrick


    The problem is that the intended purpose of the timed signal: preventing speeding, in fact incentivizes speeding, particularly, as huh mentioned, with the lights being so long. You can go far more than a couple blocks at 40mph. I drive and bike Fell and Oak everyday and I can assure you there are speeders constantly, and going well over 40mph for many blocks. It takes quite a while to catch up to the pack, and you can speed the entire time, at least 5 blocks.

    People always talk about enforcement, but even with good enforcement (which does not happen on Fell and Oak) you can only catch a small fraction of the violators. Enforcement is not the answer, proper design for safety and use by all modes: car, bus, bike and foot is what is sorely needed on Fell and Oak.

  • Dunce


    Valencia, Sunset and Great Highway are all examples of what’s called “single alternate” traffic signal synchronization. If you numbered the signals along a street, then signals 1, 3, 5, 7 etc are all green while signals 2, 4, 6, 8 etc are all red. They all flip at (about) the same time, hence the “alternate”. It’s easy to watch this occur on Valencia (between 16th & 25th streets).

    As others have commented above, one-way streets with typical signal progression encourage speeding in order to “catch up” with the platoon, especially late at night when there is light traffic.

    However, the beauty of the single alternate system (whether on one-way or two-way streets) is that it is ALWAYS impossible to drive faster than the set speed. If you drive any faster, you will arrive at the next intersection on red.

    Many drivers on Valencia have yet to figure this out–they drive 25 mph just to come to a stop at the red ligth. Signage advising 15 mph could help get the message across. Regardless, the single alternate system is the safest from a pedestrian safety, speed regulation, and red-light-running perspective. It would be great if MTA deployed this signal timing approach across the city.

  • I like the idea of making Downtown streets 2 way again. It would be wonderful if for no other reason than out of towners would no longer get lost so easily on grids they do not know how to negotiate. It would also stop drivers from flying across multiple lanes to nab parking spaces. It is time to make SF streets slower but more navigable.


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