View Full Version : Running out of electrons and traffic engineering

2008-Jun-05, 05:37 PM
Some "possible tornados" and thunderstorms "ravaged" (according to the news) the DC area, and since 3pm yesterday, I am utterly powerless, so to speak (yes, I have a thirst for power, but only when the lights go out). In addition, some stoplights are out.

What's interesting is that one would expect the areas with no stoplights to suddenly
turn into a parking lot. However, getting home from work yesterday and returning to work today I had some of the fastest commutes ever--and no, I wasn't on the main road blazing through dark stoplights meant for side roads either--I made a right turn, and a left turn, both at dark lights, one from a 4-lane to a 6-lane, and then from that 6-lane to a major highway 6-lane, both much faster than usual--hardly any traffic ahead of me that would otherwise be waiting for the light--and we just alternated (without help from a policeman even!). I stopped literally for 3 seconds then made the turn, both times. On a normal day, I typically wait several minutes, both cases, for the light to change, and am behind quite a line of traffic (and sometimes have to wait for two turns of the light to get through as a result).

This is counter-intuitive, especially since one purpose of the stoplights is to regulate traffic flow to reduce traffic jams. Now, maybe people are just staying home as a result of the power outage...but I doubt it.

I think there may be an as-yet undiscovered principle here--maybe the stoplights are in fact counter-productive? After all, yellow lights are "time wasted" since for a portion of them, nobody moves in either direction (or, it's supposed to be like that), and lights are often red with no traffic coming the other way, only to turn green just as some cars are pulling up and stopping from the other direction, and anyway, the line behind the light waiting for it to change itself takes a bit of time to get started because of the "accordion effect". Could all this be negating the benefits of the traffic regulation?

It could be screaming for more intelligent traffic lights, or just plain fewer lights!


2008-Jun-05, 05:58 PM
Well, it depends on traffic congestion and perception too. When a traffic light is out, people are suppose to treat the light like a stop sign. 'Round here, 90% of them think the "more major" road just gets to ignore the light. Idiots. Anyway, I digress.

If it's heavy traffic, you spend less time "at the light", but you still wait in line for your turn to get to the light. The flow might feel more even, but one has to wonder about the overall time spent "in line" compaired to "stopped at the red light".

The other thing to consider is ease of use to drivers. You mentioned 4 lane and 6 lane roads. If there's heavy traffic, how confusing can it get if six cars pull up to a "stop sign" at the same time on the same road. Then throw in other cars at the intersecting stops. It's really easy for people to get confused on who now has right-of-way.

And the intersection has to work through all phases of traffic congestion. A stop sign might be more economical for 18 hours of the day, but if it doesn't work for the other 6 (morning/evening commute times) then it doesn't work at all. Though there are intersections that go from "normal" traffic lights to flashing reds depending on time of day. I've never been to DC, but I'd imagine that depending on what's going on, it might be hard to nail down specific times where flashers would be better than red-yellow-green'ies.

That being said, I come from Central Ohio...the land of the inept traffic engineers. So often, a little foresight and planning, mixed with a generous but not unreasonable ammount of common sense, could go a long way to making roadway/transportation system design much better.

2008-Jun-06, 12:53 PM
Perhaps it's a matter of everyone tending to watch out more when approaching a black traffic light, while the lit ones have to adjust the timing to take into account that people don't look at anything but the light to decide on whether to go and will drive on green whether there's anyone there or not so it has to be delayed enough to guarantee the cross traffic is out of the way.

2008-Jun-06, 01:02 PM
I'm guessing that the majority of trips would indeed be quicker without lights, but that some people would get stuck for many minutes at certain intersections, and the accident rate would be horrendous!

On the other hand, the novel "Time and Again" by Jack Finney has a marvelous description of a traffic jam in Manhattan, in 1882, before traffic lights were invented. That would not fit in with my hypothesis.

2008-Jun-06, 06:01 PM
I was in a horrendous jam this afternoon after getting lunch--not the same lights that were out (but are back on, and yeah, I have my electric back after about 36 hours of darkness) though those lights were also back to their old slow, traffic-backed-up selves. I couldn't see an obvious cause to the jam except--two lights in a row seemed to be short-cycling AND almost perfectly out of sync with each other. Sounds like such a strange failure mode it makes me think some attempt at syncing the lights actually had a bit flipped or something.