Tuesday, April 24, 2018

Synchronized signals - bane or blessing?

Synchronized lights were an invention of the 1950s. So why can't Baltimore City get it done in the the 21st century? Can't they or don't they want to?
Old time intersection management Baltimore

The matter is all over the media since Council President Jack Young introduced a resolution yesterday which demands that Baltimore DOT first get their signals synchronized before they start their new initiative "don't block the box" and start fining violators who clog up intersections. Young has observed that frequently cars get the green light just to be caught at the next signal being red, creating stop and go traffic and drivers who didn't expect to be stopped again so quickly being stuck in intersections. Sounds like a plausible request, doesn't it? Although Young may have taken it a bit far when he requested "that the free-flow of traffic is ensured". In fact, with that demand he brought us right back to Henry Barnes who introduced all the one way streets to Baltimore, chiefly for this one reason: Better flow of cars. Real synchronization of signals is only possible on one way streets, because it means a progression of green lights that rolls along a street at the same rate as the cars move. This dynamic can't work for two way streets, because the two "waves" of green would roll in opposite directions and be in conflict with each other.

Barnes, Robert Moses and the whole idea that city streets are only there to move cars as freely as possible have been discredited in our time when we talk about "complete streets", livable and walkable cities and multimodal transportation that gives preference to walking, transit and bicycles over drivers in cars who are eager to leave town as quickly as possible. So how does the synchronization debate fit in?
Ancient Baltimore traffic signals
(Druid Heights)

Residents on Calvert and St Paul Streets in Mount Vernon have long complained about how the perfectly timed signals along this pair of one way arteries have turned residential streets into raceways. True, synchronized signals can manage speed only to some extent by forcing the lead cars to go the speed limit to perfectly hit the "green wave". But inside the 20-60 second green phase aggressive drivers can play catch up and speed to get into or beat the rolling green lights, especially when they enter from side streets and floor it to avoid the next signal turning red on them. So there are traffic safety reasons that would make traffic engineers not want to synchronize signals all too well.

And then there is technology. As previously explained on this blog, Baltimore's signals and their central controllers are old and the layers of technology that have been added to the originally fairly simple operations of the 1950s have made things worse, not better. Sensors embedded in roadways,  which are supposed to influence the signals based on actual traffic volumes, are prone to failure. In many cases there is no good record at DOT where those sensors are, let alone a proper repair log. The coordination of signals requires timers, and implausible as it seems, the reality according to DOT engineers, is such that each signal has an individual timer which, like a real clock, can fall out of sync and cause a slight creep in asynchronicity, requiring DOT staff to reset the timers every so often.  Modern computers and camera based sensors would eliminate this problem, but many signals are not on those up-to date systems and one can only imagine how those would be maintained.

Finally, there is traffic volume. When there are more cars than a green phase can handle, traffic will back up, no matter what. Especially during rush hour that is often the case. When even four lane roadways without any signals, such as the beltway or the JFX, routinely back up, how would the same not also happen on city streets with signals, merging buses, pedestrians in crosswalks and cars backing into parking spaces?
Houston signals: Synchronized on a one way street

Barnes and Robert Moses saw traffic back-ups as an insult to their profession they had to avoid at all cost. So they built freeways, eliminated streetcars and optimized flow wherever they could, with the result that transit, walking and bicycling plummeted and people with cars moved further out, the faster they could drive, the further . The more traffic was "optimized" the more people needed or wanted to drive, i.e. the more traffic there was. In short, the concept of "free-flowing traffic" is a fools errand.

We are not in this mental space any longer. We don't want to promote sprawl but urban living, we want people to be able cross a street safely on foot and we want lively, attractive streets along which one wants to live.
Nashville signals: Two-way can't be synchronized in both
directions at one

No wonder, then, that DOT was not available to respond to Jack Young's resolution on a day in which three people were killed on Baltimore's streets in car crashes. They would not only have to admit that in many cases they are incapable of synchronizing lights in a lasting manner, even if they wanted to do it, they are also held by the same City Council not do it.

Still, gridlock due to bad signal timing is in nobody's interest. It blocks cars, pedestrians, bicyclists and buses alike and unnecessarily fouls the air.

No matter how bad the traffic is, nobody has to "block the box", a quick glance is sufficient to see if there is space on the other side of the intersection.

Klaus Philipsen, FAIA

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