On Scramble Crossings

DSCF3873 Peter Parker at Melbourne on Transit has an interesting analysis of “scramble crossings” at signals.  Scramble crossings are phases of a signal that give pedestrians the green in all directions, so that they can cross in any direction including diagonally across the intersection.  Sydney, where I live, has exactly one of them, to my knowledge.  It’s right in front of Town Hall.

Peter proposes that when a pedestrian wants to cross to the diagonally opposite corner of an intersection, the usual method of doing so — cross one street, wait for next signal, cross the other street — is a little like having to make a connection as part of a transit trip.  The scramble signal provides a direct trip, but at a lower frequency than you’d have if you just had the two standard crossing phases.  Frequency of a transit trip is analogous to the cycle time of the signal.

It’s an interesting analogy.  I have to say that while scramble crossings are nice when you get one,
it’s far better to just increase the frequency overall, by speeding up the cycle pattern of the signals. My informal experience is that Australian signal cycles are longer than North American and European ones, which may be one of the reasons that so few people obey them.  Long-cycle signals have the particular disadvantage of encouraging red-light running, impulsive crossing, and other dangerous behaviors, because the consequence of just missing a phase is relatively high.

See also Tom Vanderbilt’s “defense of jaywalking.”

19 Responses to On Scramble Crossings

  1. Tabitha.Bos November 10, 2009 at 11:13 pm #

    Incidentally, my part of Massachusetts also has intersections that function in this manner. I like it a lot in the intersections of small town main streets, especially since you have twice as many people crossing at once, so cars don’t seem (subjectively) as likely to risk taking a right-on-red into one’s person.
    StreetFilms also has one on this, a la the infamous Bike Box video: http://www.streetfilms.org/barnes-dance/

  2. Adam Parast November 11, 2009 at 1:43 am #

    Does anyone know of a study that looks at the safety impacts of long signal cycles?

  3. Mike November 11, 2009 at 4:32 am #

    Isn’t the corner of George and King Streets in the city the same? The Taylor Square crossing on Oxford St certainly is one and I’m sure there are more.

  4. Nathan Williams November 11, 2009 at 8:13 am #

    I find that with concurrent pedestrian signals, crossing both streets is relatively easy, since you just take whichever crossing is currently available, and then have a short wait (cycle time minus your crossing time) for the walk signal in the other direction. With LPI (as they have in most intersections here in Cambridge, MA) you’re even guaranteed to take possession of the right of way before the automobiles. I find the longer delay for the all-way stops (as in neighboring Boston) much more annoying, and indeed, it does lead to more impulsive crossing.

  5. John November 11, 2009 at 12:53 pm #

    I agree that I’d usually rather have less delay than a comletely new signal phase for pedestrians only. It really has to be a unique situation to consider a ped-only (Barnes Dance) scramble phase.
    Another analogy:
    At locations with physically separated bike lanes where the bikes get their own signal phase, I think this is the same problem. Instead of just a N/S and an E/W phase, you now have a N/S, E/W, and a Bike-Only phase. This increases delays for everyone, including the impatient cyclists who would might be better off riding in mixed traffic.

  6. Ted King November 11, 2009 at 1:01 pm #

    Thank you for pointing out the “scramble crossings” moniker. San Francisco has quite a few of these in its CBD. I have heard that pedestrian convenience was NOT a factor. Instead it was improving traffic flows in an area with a lot of one-way streets. Pedestrian safety was also a factor. I’ve been in that area during an evening rush hour and the tidal-bore-like herd of metal pachyderms (up to five lanes in width) is very intimidating. Having a period in the signal cycle that is ONLY for pedestrians is a comfort.
    CCSF Pedestrian Quiz :

  7. J November 11, 2009 at 1:57 pm #

    Nathan, I like the crossing in Boston outside the Boylston T stop. Its a hybrid. When cars get green, theres an accompanying pedestrian light in the same direction. However, every cycle theres an exclusive pedestrian crossing as well. This makes up for the fact that for about 5 seconds before the pedestrian cycle, cars have the exclusive right of way so that they can turn.
    Unfortunately, there is no standard in Boston for pedestrian crossings. Other lights with exclusive pedestrian phases say do not cross at all other times, even when it is safe to cross. Others have exclusive phases which operate only when the button is pressed.

  8. EngineerScotty November 11, 2009 at 3:03 pm #

    I was wondering when someone would utter the words “Barnes dance”.

  9. Pantheon November 11, 2009 at 3:56 pm #

    I have never experienced one of these stops, so I can’t comment on the relative convenience of them. However, I agree with Ted King that it is safer and rather nice to have a crossing that is only for pedestrians. At a typical intersection, you are NEVER safe the moment your foot leaves the curb. You are always wrestling with cars who are turning right, turning left, or blocking the crosswalk. That you have the “right of way” isn’t much comfort, because it is you who will die upon collision.
    From an engineering standpoint, this is a good way of eliminating conflict between drivers and pedestrians. At different times the intersection unambiguously belongs to one or the other, creating a more comfortable situation for both.

  10. Alon Levy November 11, 2009 at 5:10 pm #

    From a walkable neighborhood inhabitant’s standpoint, this is a bad idea: it reduces the percent of time that pedestrians have to cross the street. The usual way of operating streetlights gives both pedestrians and cars a green light for about half a cycle. The more phases you add, the longer each side has to wait, or the less time each has to cross. In Tel Aviv it’s gotten to an extreme: it’s normal to wait a minute for a green light that will last maybe 20 seconds.
    The only times this is justifiable are when traffic is so heavy that pedestrians and turning cars would conflict too much if they shared a cycle. Having lived in Tel Aviv, Singapore, and New York, I know of only two places where foot traffic really is this heavy: Times Square, and its Singaporean equivalent, Orchard/Paterson. I think Shibuya and Shinjuku Stations in Tokyo have crosswalks with even more foot traffic, but no other city I’ve been to has anything even remotely like Shinjuku or Shibuya.

  11. EngineerScotty November 11, 2009 at 8:41 pm #

    Such things are useful in districts where pedestrians are the dominant form of traffic. I believe that Seaside, OR has one of these on Broadway Street (the main pedestrian drag in this resort town), I’ve seen them in SF in Chinatown as well.

  12. Daniel November 12, 2009 at 4:26 am #

    Not many in Melbourne. Here’s a short video of the most prominent, outside the Elizabeth St exit to Flinders St Station. http://www.danielbowen.com/2009/06/19/move-people-efficiently/

  13. Capn Transit November 12, 2009 at 8:09 pm #

    If you call them “pedestrian scrambles” as seems to be popular in Oceania, you run the risk of forgetting their history and one of their early promoters, Henry Barnes, who was transportation chief in (successively) Flint, Denver, Baltimore and New York. I’ve seen the largest number of them in Denver.
    It’s very important to make the distinction, as J does, between intersections where the only chance for pedestrians to cross is the Barnes Dance, and those where the Barnes Dance supplements phases where pedestrians are allowed to cross with parallel car traffic. In your analogy, it’s like having the option of either transferring now or waiting for a direct bus or train.
    I like the supplementary Barnes Dances, but I have much more mixed feelings about the ghettoized Barnes Dances.

  14. Teresa November 13, 2009 at 10:21 am #

    I’m surprised that anyone would cross at an intersection, especially a busy one. It is the most dangerous place to cross.
    If you cross in the middle of the block [also called jaywalking] you have only two ways to look–left and right.

  15. EngineerScotty November 13, 2009 at 12:18 pm #

    Intersections are where the crosswalks and signals are, after all… and where drivers are expecting to encounter pedestrians.

  16. Peter Parker November 14, 2009 at 11:54 am #

    Teresa, a couple of comments/observations.
    1. Merit of crossing in the middle of the block rather than at a signalised intersection.
    I agree it can be superior, but only in the following circumstances.
    a. The road is moderately busy only, and/or
    b. the crossing point has signalised intersections either side (to ensure traffic flows in bursts rather than continuously, as would happen through an uncontrolled intersection or roundabout), and/or
    c. The road has a median strip or pedestrian refuge (these are not all good, however, but this is a topic for a seperate article)
    If at least one of the above is not satisfied, it may be preferable to trade the certainty of an assured pedestrian cycle for the (probably) quicker average access across an unsignalised road. Luckily the street between my place and the railway station does meet these requirements and I do find it safer to cross midblock as it’s mostly away from turning vehicles (that sometimes have to cross the railway track).
    2. Definition of jaywalking.
    Your definition is common, but the following are also referred to as jaywalking
    a. Crossing against the lights (eg on a red man)
    b. Crossing obliquely across the road (ie not taking the shortest trip between two sides of the road – I wish the latter could be made into a general pedestrian access right!!!)
    Probably because I went to school in a town too small for traffic lights, b is the definition I’m most familiar with. While we do have rules for crossing the road at a point other than at a signlised intersection or crossing, this rule, at least in Victoria, is quite liberal – the distance is only about 20 metres, making the prohibited zone quite small. http://www.vicroads.vic.gov.au/Home/BicyclesPedestrians/Pedestrians/Pedestrians.htm

  17. M1EK November 16, 2009 at 7:21 am #

    It’s a bad analogy – because when you’re walking you’re very rarely ONLY doing the diagonal – more likely you need to go 3 blocks down, then a block up; or something like that.
    The normal course of action there would obviously be to continue straight on your side when you have a green; and cross to the other side whenever you hit an intersection where the light has changed to red for your direction. IE, you can decide when, of 3 possible choices, to do your perpendicular cross – based on what will obviously be faster; not really an option with transit.

  18. Stuart Donovan November 18, 2009 at 2:14 am #

    While the analogy was, I suspect, slightly tongue in cheek I think there is a fundamental difference between scramble crossings and connective PT networks.
    In the latter’s case you can design the network to “enforce” passengers to transfer at key locations. There is little “push back” from passengers other than those who elect not to travel.
    When it comes to scramble crossings, however, we must contend with wonderfully stroppy pedestrians. Pedestrians, for whatever reasons, seem to like scramble crossings.
    There are several such crossings in Auckland City (pop 1.2 million). The City did a study where they reverted some of these to standard phasing, with the result being than many pedestrians, instead of waiting, simply jay-walked upstream.
    This pedestrian “push-back” created additional safety issues and undermined any incremental increase in capacity that came at the intersection.
    So I think there is an essential difference between scramble crossings and connective PT networks, and that difference relates to the complexity of the system being analysed. People are (thankfully) often stubborn and irrational.

  19. numbat January 22, 2010 at 6:30 am #

    We have quite a few scramble crossings here in Perth, but they are only used at major CBD intersections with high volumes of turning traffic which create pedestrian/vehicle conflicts. At these intersections, there are no pedestrian movements allowed on other phases (unless one of the streets is one-way).
    Unfortunately, our traffic planners haven’t quite cottoned on that this combined with abominably long cycles (one intersection I go through regularly, 3 blocks from work, has a 5 minute long cycle during peak hours) results in a jay-walking culture.