Saturday, January 18, 2014

Walk audit of Union Square, Allston and suggestions for the future

Union Square, Allston. The view from the Twin Donuts shop, facing east.

(Updates in bold posted 12th November 2015).

Let's take a look at Union Square in Allston, a vibrant neighborhood of the city of Boston. This is the convergence of several busy streets, a transit hub for buses, a retail district, with an elementary school and plenty of nearby residents living within a few minutes walk. I will call this a kind of "audit" because it is based on my observations, as an outsider. The audit uses timings from a weekend study. The main difference between a weekend and a weekday here is length of the full cycle: 90 seconds on the weekend, 110 on the weekday. Adjust accordingly.

Union Square, landmarks and street names. All satellite imagery courtesy Google.
Click on it for larger view.
Key points from below the jump:
  • The "level of service" given to the Union Square intersection, by the New Balance transportation study, is "D" (35s to 55s average delay/vehicle) during weekday a.m. peak and "E" (55s to 80s delay/vehicle) during p.m. peak and Saturday peak. "D" is considered normal in cities.
  • Traffic levels have declined by about 5-6% here since 2002.
  • An examination of the signal schematic (below) shows that for cars, no direction of travel has to wait more than 72 seconds to be given a green phase, on a weekend.
  • Yet, the minimum time for a pedestrian to cross Union Square (north/south), legally, is about 100 seconds, if you happen to arrive at the intersection at the optimal moment in the cycle.
  • For the less lucky, the expected crossing time is about 145 seconds with a worst case of about 190 seconds.
  • For the less capable walkers, the worst case is about 258 seconds. If you happen to be elderly, or a young child. the city expects you to wait 4.3 minutes to cross 95 feet. That's a rate of 0.25 mph.
  • The green right turn arrow given to traffic moving eastbound from Cambridge Street is in direct conflict with a walk signal for people crossing between the school and the fire dept station (see picture below).
  • The 21 seconds of walk phase given to the 110' crosswalk of Cambridge Street between the Jackson Mann school and Twin Donuts is not enough time for a healthy adult, much less a person with disabilities or a child going to the school.
  • There is no crosswalk marked at the Hano Street bus stop, despite heavy ridership. Instead, the city put up a new sign telling pedestrians not to cross there, in response to a tragic crash.
  • In the long-term, a Poynton-style redesign should be seriously considered, with a shared space design such as a single-lane roundabout (or similar) completely replacing the traffic signal-controlled intersection. All users of the intersection would benefit, as would the surrounding neighborhood.

Here is a visual summary of the traffic signal programming at Union Square, based on my observations (not schematics). This intersection is slightly unusual in that 2-way travel is the exception, not the norm. BTD opted for unobstructed left turns for most of the cycle, rotating through the streets so that each gets an exclusive turn, and it repeats on a 90 second cycle (weekend). During the weekdays, the cycle scales up to 110 seconds. Walk phases are shown with dashed white lines, and are usually 1-2 seconds shorter than the green phase.

Union Square traffic signal programming, weekend. Phases go around clockwise.
Yellow clearance = 4 seconds, red clearance = 1 second.
It's fairly effective at moving vehicles through the intersection, if sometimes a bit confusing for newcomers. Barring queues, the worst case for a car is that it is traveling eastbound on Cambridge St, gets caught by the yellow, and has to wait 72 seconds (weekend) for a green light. The design reflects a choice of speed over responsiveness for drivers. You may have to wait on a queue at the light, but once you get the green, it's full speed ahead -- with all the attendant dangers that implies.

This choice of design by BTD also implies that pedestrians must take at least one full cycle in order to cross the square -- from the shops to the plaza, for instance. In fact, counting walking time for a typical adult, and if you follow walk signals strictly, then the minimum time it takes to cross from the shops to the plaza is about 100 seconds. That's assuming the best case scenario. More typically, on a weekend, it will take you about 145 seconds (over 2.40 minutes) to "legally walk" from north to south, a distance of 95 feet. Few people will actually wait for such terrible timing.

An example of how the minimum was calculated shown below, using timings from the diagram above.

Minimum crossing time (weekend), following pedestrian signals, from shops to plaza.
In reality, you need to figure that you might arrive at the crosswalk with equal chance for the intersection to be at any point along the 90 second cycle. No matter when you arrive, you will be forced to wait either at the curb, or at the pedestrian refuge island. Therefore, for random arrivals, you should expect about 45 seconds of additional delay above the minimum, for a total of 145 seconds expected time to cross the square on foot. And if you are a slow walker, then you must add another 68 seconds to complete the two stage crossing of Cambridge St, bringing it up to 213 seconds, or three and a half minutes. In the worst case, you have assume that you will wait a full cycle of delay, meaning that your times are 190 seconds. That goes up to 258 seconds if you are both unlucky and unable to walk quickly.

BTD expects pedestrians to walk this 110' crosswalk in 21 seconds or less.
Or wait a cycle in the refuge island.
BTD assumes that people can cross Cambridge St in about 21 seconds, which implies a walking rate of over 5 ft/sec, which is extremely fast even for a healthy adult. So it's quite likely that the users of the crosswalk will not be able to complete it in one stage. I even had the opportunity to observe that happening to a few 20-somethings who happened to cross while I was doing measurements. They seemed surprised at how short the duration was. Of course, like everyone else, they just waited until it was clear, and ignored the pedestrian signal. For them, it was just another example of how untrustworthy the pedestrian infrastructure is around here.

The Union Square traffic signal system has three cases where pedestrians are shown a "Don't Walk" phase at a time when it is actually perfectly safe to cross because of no conflicting traffic. Most people figure these out pretty quickly on the ground. I will leave it as an exercise to the reader to figure out the three cases from the phase chart above. Instead, I will point out a case where the signal programming explicitly directs cars to drive into the path of crossing pedestrians:

The green right turn arrow sends cars directly at pedestrians crossing with the signal.
This occurs in the lower-left corner of the chart, when Brighton Ave is given the green light, but also a green right turn arrow is displayed for Cambridge Street going east -- in conjunction with a red ball. Technically, this arrangement has an explicit legal meaning (720 CMR 9.00):
When a green arrow is exhibited together with a red or yellow lens, drivers may enter the intersection to make the movement permitted by the arrow, but shall yield the right of way to vehicles proceeding from another direction on a green indication, and to pedestrians legally within a marked crosswalk.
However, I'm pretty confident that few, if any, drivers are actually aware of the subtleties of this particular regulation. The manual doesn't mention it. It's another example of a rule that works in a perfect theoretical world where nobody imports customs from other locales, and everyone is aware of all the precise meanings of every combination of signals. In practice, most people take a green arrow to mean what it usually does: an exclusive right-of-way that allows you to zoom through the intersection with confidence. As you can see, cars go through pretty quickly:


(Update: at some time in the past year, the confusing green right arrow was removed: so these past few paragraphs are out-of-date).

I hope that by this point, you have realized that the intersection is confusing for pedestrians and what little infrastructure provided for them is fairly untrustworthy. In fact, most people use their eyes and ears to protect themselves, which is the wise course of action. However, the nature of a traffic signal-controlled intersection sometimes creates dangerous situations where a driver, operating under the certainty of a green light, is unable to stop in time to prevent a tragic crash. This resulted in the death of 12-year old Barrington Brinson, last year, apparently while on his way to catch the 66 bus to school in the morning.
“The area where the accident happened is a traffic nightmare on a good day,” said ­Marian Fuscolda, who teaches at the Horace Mann School for the Deaf and Hard of Hearing, which is next to Jackson Mann. “There are cars coming this way [and] that way from all directions trying to zip through to beat the lights.” 
Though there is a web of crosswalks to help pedestrians get through the busy X-shaped crossroads, many people dash across the streets at other places. 
“I jaywalk all the time here, because at the lights it takes way too long; it’s just a pain,” said Madeleine Streit, who lives across the street from the fire station.
The city has refused to install a crosswalk at the Hano Street bus stop so far, even though a comparable example already exists on the other side of the intersection. Instead, the site of the crash now has a new sign, one which expresses the city's priorities towards the people living in the area:

The no crossing sign at Hano Street
As anyone involved with the effort down the street at the Cambridge Street overpass knows, it is very difficult to get a crosswalk installed in this town! And even though BTD has professed the principles of Boston Complete Streets, they are still reluctant to move quickly on longstanding problems.

(Update: BTD installed a crosswalk with flashing button-activated lights in the beginning of 2015).

So what should be done about Union Square?

I believe that I have identified some issues for which some minor changes can help workaround some outstanding problems. Changes in signal timing, phases, and street markings are a start, and may have to do, for now. But there is a much larger problem at hand: the existing design of the intersection is not very neighborhood-friendly, and probably never can be in its current form. The high skew of the intersecting streets creates unavoidable problems for pedestrians and vehicle users, in the context of a traditional traffic signal controlled intersection.

Eventually, both Brighton Avenue and Cambridge Street will be up for reconstruction, and I believe that a drastic change should be seriously considered: conversion of the signaled intersection into a single-lane roundabout or similar shared space design.

Recently, I had occasion to observe a traffic signal breakdown at weekday p.m. rush hour in Union Square. It was rainy, dark and a bit foggy, and for unknown reasons, the traffic signals had switched to a flashing red/yellow combination instead of the usual 110 second cycle. Conventional traffic engineering wisdom would suggest a chaotic breakdown, with queues piling up, drivers slamming into each other, and all sorts of bad things happening. Of course, none of this doomsaying actually came to pass. Instead, drivers slowed down, showed their intentions, and negotiated their way through the intersection. Some pedestrians figured it out immediately and used body language to communicate their intent to drivers. Others were bewildered and insisted on waiting for the "Walk" signal that was not going to come. Despite the fact that the current configuration of the road is not well suited towards signal-less operation, even at rush hour it managed to clear traffic, under less than ideal circumstances.

If such an ad-hoc, unplanned, chaotic scenario can work out, then I think that a properly designed, channelized, pedestrian-friendly, single-lane roundabout (or related design) would actually do quite well in this spot, and probably remove a lot of the frustration that currently hovers over it. Certainly, it could not be worse for pedestrians than the current layout is. Roundabouts and other kinds of signal-less infrastructure have become more popular in recent years, thanks to the work of engineers such as Hans Monderman, and a growing realization that classic traffic engineering does not have any scientific basis, and is largely a matter of arbitrary custom, not safety.

I believe that the example of Poynton, UK is actually quite similar to that of Union Square, Allston. A struggling town center, crossed by a street feeding the highway, with heavy traffic, including many trucks. Their neighborhood was suffering greatly under the burden, with deadly crashes and an unforgiving environment. Traffic engineers had applied many of the same techniques which are currently deployed in Union Square, to no avail.

If you watch the video, you will see a transformation of that town center into much nicer place, one which still manages to handle the same burden of traffic, yet also creates a pleasanter neighborhood for walking, biking and local business. Drivers also report much less headache with the "double roundel" shared space scheme than with the prior, traffic light controlled intersection. Several blind or disabled persons are also interviewed, and they express satisfaction with the new design.

I don't see this happening anytime in the near future, for several reasons: the streets are not up for reconstruction yet, the custom of traffic engineering in the United States has not yet caught up with the rest of the world, and there is a great deal of status quo-bias that needs to be overcome. However, hopefully by the time the city gets around to reconsidering this intersection, it will be ready to seriously consider Poynton-style shared space designs which have the potential to dramatically improve the local neighborhood for all residents and visitors.

(Update: some good perspectives on Poynton from a knowledgeable visitor; in short, some success for walking and driving, but it was not designed with any cycling provision at all -- a major mistake).


  1. Honestly, the fact that Union Square and the Harvard Ave at Commonwealth Ave intersections don't have at least one or two fatalities a day is probably a miracle.

    I was once waiting for the 64 on Saturday morning and this old lady with a shopping cart was trying to cross the street to Wallgreens. She waited for traffic to clear, but as soon as she did two cars came down Cambridge Street, one after another. The first car, which could see her, stopped, but the second just went around the first one so it wouldn't have to slow down. Thankfully he didn't hit her, but I've never been more shocked by Boston's bewheeled murderers.

  2. Thankfully, Boston has since changed its mind and installed a crosswalk at Hano Street for the bus stop. But really, that whole area needs to be reworked.

    1. Yes, the crosswalk was one of the issues that we were able to have fixed, last year. I'm proud to say I helped out, but of course, I was only one of several people working on it. A change came from the top, the mayor came to visit with the family of the boy, and the commissioner of BTD as well. Nothing will ever bring him back, but perhaps this change in attitude, and the new Vision Zero policy, will help prevent such tragedies in the future.