Beware the HAWK

There will be no green light at the traffic signal that will regulate the new pedestrian crosswalk over Mass. Ave. in Arlington Center.

At that location, drivers and pedestrians will encounter a new kind of traffic signal unlike any in the area. The potential for confusion, and even injury, is real.

Phase-by-phase diagram of HAWK signal

There’s no green. Click for larger. Source: U.S. Federal Highway Administration

The signals are in place and will be activated later this year. The crosswalk has already been painted in across Mass. Ave. at Swan Place, near the eastern trail head for the Minuteman path.


Under Wraps: The HAWK signals are in place though not operational. Note the triangular arrangement of lights.

The new signalized crosswalk is the single greatest new amenity for pedestrians of the entire Arlington Center Safety Project, now mostly completed (except for activation of lights and signals).

The technical name for this light is a pedestrian hybrid signal, but traffic planners like to call it a HAWK beacon, for High-Intensity Activated Walk beacon.

Although I described this signal early last year in another report, the topic deserves its own post. Here I focus on what drivers, pedestrians, and cyclists will see throughout the light cycle, and what we are all supposed to do there.

Phase One: Crossing Requested.

phase1Don’t Walk; flashing yellow

When a pedestrian arrives at the crossing, there will normally be a standard Do Not Walk signal visible from across the street.

Pressing the button will activate the light cycle, which begins when a flashing yellow light alerts vehicles that traffic must soon stop for the crossing. The Don’t Walk signal remains unchanged.

The cycle will also be activated by cyclists who stop at the mouth of Swan Place. Actually, all Swan Place traffic must stop for the stop sign there. However, there will be no signal at all for vehicular traffic (which includes bicycles) coming from Swan.

Consequently, cyclists and motor vehicles may proceed into Mass. Ave. traffic at any time it is safe to do so after a stop. In that respect, the situation for cyclists and drivers is unchanged, but less-experienced cyclists may prefer to wait for the light to stop traffic before proceeding.

The start of the cycle may be delayed to coordinate with the traffic signals a block away at Route 60.

Phase Two: Crossing Immanent

phase2Don’t Walk; steady yellow

In Phase 2, the blinking yellow light turns steady yellow. Like a conventional yellow traffic light, this is a sign to prepare to stop.

Pedestrians continue to see the standard Don’t Walk signal.

Phase Three: Pedestrian Crossing

phase3Walk; double red

Next, the standard Walk signal tells pedestrians that traffic is stopped and it is safe to cross Mass. Ave. Cyclists and motorists on Swan place, however, may still enter traffic on Mass. Ave., yielding to pedestrians in the crosswalk.

For Mass. Ave. traffic, note that the stop signal comprises two red lights. They still mean stop.

Phase Four: Complete Crossings

phase4Flashing Don’t Walk with Countdown; alternating flashing red

This phase will also be familiar to pedestrians: a flashing “Don’t Walk” signal means that traffic is still stopped, but pedestrians who have not entered the crosswalk should wait for the next cycle.

Mass. Ave. traffic, however, will encounter something new, as the two red lights will begin alternatively flashing. This is visually the same signal deployed at rail crossing, where the meaning is, essentially, “For goodness’ sakes stop if you value your life.” It has a very different meaning in a HAWK, however.

Here, this signal gives notice that traffic will shortly resume and also signifies “proceed with caution after a stop,” and after yielding to any pedestrians in the crosswalk.

In theory, a driver who stops for this signal can assess whether it is safe to proceed based on who, if anyone, is in the crosswalk at that time.

Pedestrians will have the flashing “don’t walk,” meaning “do not enter the crosswalk.” However, pedestrians may be surprised to find that vehicles are not stopped by an unambiguous steady red during this phase.

The 100% plans for this project indicate that there will be a countdown display in the pedestrian signals showing how many seconds remain in this part of the cycle.

Phase Five: Mass. Ave. Traffic Proceeds

phase5Don’t Walk; no signal

That’s right—the signal goes dark for this phase, indicating traffic is free to proceed.

This signal is cousin to the warning beacons at rail crossings and fire stations, which similarly go dark to indicate there is no restriction on forward motion.

With the HAWK, the pedestrian signs are familiar, but traffic is supposed to proceed when it has no signal, and slow or stop in response to yellow, red, and flashing red.

There’s no green, ever.

HAWK signal

HAWK beacon animation courtesy of KJBurns.

Arlington has already experimented with a nonstandard signal where the Minuteman path crosses Mill Street. There, flashing lights alert Mill Street traffic to the presence of cyclists or pedestrian on the path.

Though this signal generally seems to make drivers more cautious, there is no specific requirement to slow or stop associated with the signal, as there is with the HAWK.

On paper, the HAWK beacon is less impactful to traffic than a standard crossing signal. The flashing red phase shortens the time during which traffic must stop completely.

However, untutored drivers might slow things down by not proceeding at the unfamiliar double red flash, or by failing to drive in the absence of a green light once stopped by a red. (Possible reactions: Where did the light go? Is it broken? What do I do?) A driver who waits for green will wait forever.

If not calibrated correctly, the signal might also activate in response to cyclists who are continuing without waiting for the walk signal, needlessly delaying Mass. Ave. traffic.

Other errors could jeopardize pedestrians in or entering the crossing, if for instance a driver treats the steady yellow as a signal to speed up before the light change. A confused driver might also fail to treat the blinking double red like a stop sign and instead follow the leading vehicle. Either behavior could endanger pedestrians.

Furthermore, some pedestrians who are used to a walk cycle that is completely protected might enter the crosswalk, possibly at high speed, to “beat” the countdown at the end of the “Finish Walking” cycle (Phase 3, above). This behavior carries new risks because  motorists will have the flashing red signals permitting forward motion, not a steady red as with conventional crossing signals.

These signals are new to us but are no longer strictly experimental, having been incorporated into the Federal Highway Administration’s Manual on Uniform Traffic Control Devices in 2009. However, the HAWK was originally developed (in Tucson) for uses mid-block, to avoid the complications of traffic from side streets.

Indeed our use of it contradicts two suggestions in the Manual: first, that such signals “should be installed at least 100 feet from side streets or driveways that are controlled by STOP or YIELD signs” (such as Swan place), and second that

parking and other sight obstructions should be prohibited for at least 100 feet in advance of and at least 20 feet beyond the marked crosswalk, or [else] site accommodations should be made through curb extensions or other techniques to provide adequate sight distance.

We’re not doing that on the north side of the crossing.

These requirements are just guidance, and furthermore the FHA approved this signal where it is. But whatever happens here, we are breaking new ground, and other towns will be watching to see how things work out.

In the mean time, get ready for the HAWK.

Update: Bob Sprague, writing at, gently takes me to task for my  headline. His is a fair point, but note that “beware” means “be aware,” not “be afraid.” (Okay, maybe “be wary,” but I can own that.)

I do feel, a little, as though I am sounding an alarm about this new thing, because it’s going to be a head scratcher and I really hope a lot of people learn about it before they encounter the HAWK in the wild. Towards that end I am pleased that this post has gotten north of 1500 hits as of today (February 9).

Don’t panic, but do spread the word!


9 comments so far

  1. Charlotte Keys on

    Gosh. Complicated. I wish they just put a light like near the high school where it switches to red when you hit the walk button.

  2. Marian on

    Concerned for people with color blindness. Has this Hawk system been evaluated for this type of differently sighted person?

  3. Bob Sprague on

    I support the HAWK as well as this column about it. See

  4. Pepper Cat on

    I think this is going to cause more problems, most bike path users don’t stop at the stop signs on the path. I see more accidents heading to Arlington.

    • Adam Auster on

      I honestly don’t see a new bike risk, since the bike rules are not changing. I am a little bit concerned about pedestrians running into the crosswalk to beat the countdown.

      But mostly this has the potential to snarl things a little as people learn the ropes. I wrote this report so that more people would know what the rules are going to be.

  5. Adrienne Tybjerg on

    We already have completely unambiguous light signals that motorists, pedistrians and cyclists can understand. This is bizarre and probably dangerous. Just put regular lights there and stop messing around. This is not a school science project; real people’s lives and health are at stake.

  6. Crispin Olson on

    I think a UK pelican crossing offers the same features but is much easier to understand. :

    “Additionally, a pelican crossing, as distinct from a puffin crossing, has the special feature that while the green man flashes to indicate that pedestrians may continue crossing but may not start to cross, the red light changes to an amber flashing light permitting cars to pass if there are no further pedestrians. This reduces the delay to traffic. Also, pelican crossings can be used to enforce local speed limits by detecting the approach speed of the traffic, and setting the traffic lights to red if a speeding violation is detected.[citation needed] This has been found to significantly reduce the incidence of speeding in residential areas.[citation needed]”

  7. Brian Ristuccia on

    Is there an updated version of the plan showing the new configuration? The original 100% design plan showed a phasing diagram with a bicycle signal head that would have been green (!) during the flashing don’t walk / alternating flashing red phase.

    • Adam Auster on

      Or that would have stopped bicyclists during the red phase, potentially blocking motorists to whom the bicycle signal does not apply! (Can you spell “Road Rage?”)

      The 100% plans clearly show this was, indeed, the plan at one point, but the facts on the ground today show that it is not the plan any more! There is no bicycle signal head installed there, just the pedestrian one. So cooler and smarter heads have prevailed.

      My own confusion about this held up publication of this post by about a month! I have photos of the ped-only signal head that I took back in January and may yet do a separate post about the issue.

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