Computer Failure Causes Gridlock In MD County

Uncle Rummy writes "A central traffic control computer in Montgomery County, Maryland failed early Wednesday morning, leading to widespread gridlock across the entire county. The computer, which dates to the 1970s, is the single point of unified control for all traffic signals in the county, which comprises a number of major Washington DC-area suburban communities. When the system failed, it caused all signals to default to stand-alone operation, rather than the highly-tuned synchronization that usually serves to facilitate traffic flow during rush hours. The resulting chaos is a yet another stark reminder of how much modern civilization relies on behind-the-scenes automation to deliver and control basic services and infrastructure. The system remains down Thursday, with no ETA in sight."

Comments

All-green probably an urban legend

[davidwr]

Most of those boxes have a "conflicting green" detector circuit that automatically puts the signal in "safe mode" when it detects two conflicting green lights.

On simpler systems, "safe mode" is all-way flashing red lights.

I guess if you knew what wires to mess with you could disable this safety feature.

Physical access is root access.

Re:Where's a traffic cop when you need one?

[natehoy]

Wouldn't matter. The traffic lights were working fine, the problem was there was no central system that could take a larger view of traffic and sense that turning a light green a block away could prevent a gridlock issue at a specific intersection. Intelligent traffic control takes traffic that is approaching a heavily congested area and intentionally slows it down, while freeing up cars to LEAVE congested areas more quickly. They help prevent gridlock by making sure that once a specific light turns green you can actually drive through the intersection, and turns the light red BEFORE cars get caught in the middle of an intersection.

You see this kind of design a lot in well-designed roads in smaller towns. Busy towns will tend to have lots of stop signs coming in to town, but try to reduce stop signs when leaving town. The idea is to keep inbound traffic from filling the town faster than departing cars can leave by making sure cars that are leaving can do so as quickly as possible, while cars wanting to come in will be intentionally slowed down.

A meter maid has no more information about traffic flow at adjacent intersections than an autonomous single light would.

70s computer

[icebike]

Damn! 70s? Talk about Return on Investment.

The WashPost, in another article touts Fragile Technology.
I reach for my 70's era calculator and estimate the operational life of 34 years for this system. Some Fragility. Who or what at the Post has been there that long.

Wonder if its some ancient PDP version or an small IBM mainframe. The article is scarce on details. Parts for either are getting hard to find except in the scrap market.

Still you have to wonder why it wasn't ported to some other platform if nothing else as an exercise in disaster preparedness. Any commodity computer could do the job.

There is a lot of stuff like this still in service. I saw a PDP 8 monitoring turbines in a hydro Power station, and asked about where they get that fixed. The reply was it never broke down, but they had stockpiled 6 replacements, tested each yearly, just because they realized how old it was. Nobody knows exactly what it does anymore.

Re:When the system fails, shut the lights off.

[Golddess]

You're joking, right?

I mean, sure, the law states that when an intersection has traffic lights, and the lights are out, it's an all-way stop. But in practice, I rarely see other drivers actually give a fuck that they are supposed to stop.

Re:I live there

[natehoy]

Time to break out the bicycle. Or walk it, for that matter.

6 miles should take about an hour and a half at a decent walking pace, or about 45 minutes at a fairly leisurely cycling pace, and a week or so of it and your new sculpted bod will drive the ladies wild. :)

Re:And if they had been using roundabouts...

[fridaynightsmoke]

As a UK resident and driver in the true home of the roundabout, I wish to tell you that roundabouts are not a panacea.

Roundabouts work best for light to moderate traffic, where all 4 directions and all movements (left turn, right turn etc) are fairly equal in demand. For heavy traffic, they very quickly congest as traffic builds on the roundabout and blocks all entry. Indeed, round here most busy/large roundabouts have traffic lights on them as well, with varying degrees of success.

As for "gas consumption from forced arbitrary deceleration and acceleration is reduced" - I strongly disagree. Here roundabouts are used as a form of 'traffic calming', ie a deliberate obstacle to slow traffic. With a traffic light its a 50/50 chance between stopping completely and carrying on at cruising speed. With roundabouts there is always a decelerate/accelerate cycle, which depending on the design of the junction can be quite severe. In Birmingham (UK) and elsewhere. there was even a recent fad among local traffic engineers to plant high vegetation on the sightlines for approaching traffic to force all vehicles entering the roundabout to slow to below 5mph to be able to see traffic on the junction. On some examples here you have maybe 3 ft before the roundabout itself where you can see oncoming vehicles.

Don't get me wrong, I'm not saying that roundabouts are rubbish and traffic lights are good, but theres different solutions to different problems. Replacing non-synchronised traffic lights with roundabouts in a situation with very heavy traffic would have a very much worse result.