Synchronize traffice lights?

Factual Questions
1

In the city of L.A. mayoral race, one of the candidates promised to synchronize the traffic lights to relieve congestion in the downtown area. Can he do this? Oh, yes I know the mayors office can ask for this to be done, but

  1. Is it possible to synchronize the lights in a large urban city? Is it engineeringly possible? What about the left turn lanes that are only activated by a car in the turn lane?

  2. Also, is this economically feasible?

  3. Will this actually relieve congestion and make traffic flow more smoothly?

2

  1. Yes, yes, and I don’t know. For details on Seattle’s traffic light synchronization program, please refer to http://www.cityofseattle.net/td/ts_opti.asp. It has been going on for at least a couple of months, and according to the report I read in the paper awhile back, it has improved travel time along certain key corridors by as much as 30%. (The number may have been higher; I can’t remember and I had trouble finding the article in the Seattle Times’ archives.)

  2. It’s expensive, but it really depends on the city’s financial situation as to whether it’s economically feasible. Also, there are other factors to consider besides simply the cost – one of the major goals of Seattle’s program is to improve the traveling time for public transit. Buses would get priority when approaching a traffic light, etc. So if by dramatically decreasing the travel time involved when taking the bus, you get more people to take the bus, that’s an economic gain. But this is just conjecture on my part, I’m not entirely sure how the entire model would actually work.

  3. According to the reports I’ve heard, yes, it will.

A good subpage of the page I linked above is:

http://www.cityofseattle.net/td/ts_timed.asp (How Traffic Signals Are Timed) It’s a great explanation of how this works.

3

Some observations.

  1. Lights along some major East-West streets in east Portland (e.g., Halsey) were synchronized in the 60’s, if not earlier. Signs were hung above the street stating the speed (e.g. 30 MPH) they were set for, always slower than the speed limit. Definitely pre-microchip.

  2. The road I took into the UofW in Seattle in the 70’s also had synchronized lights. (Can’t remember the name.) But no signs. I figured it out and kept my bug at the right speed and frequently encountered the following: Hot Car X is waiting for the light to change, as it changes I reach the light and buzz by, within a short distance Hot Car X roars by and reaches the next light, brakes hard and waits. I reach it just as it changes and buzz by. Lather, rinse repeat. After 5 or so of these lights the idiot catches on and starts driving slower. Just as we reach the next to last light I gun it since it’s out of sync (joining another road) and just barely make the last light, leaving the idiot behind. You get your fun where you can. Also pre-microchip.

  3. Atlanta in the 80’s. No synchronized lights anywhere. Explanation? Too expensive, complicated, etc. I point out Portland and Seattle examples. Get funny looks. (Very common occurence in this part of the world.)

Note, as per the other post regarding Seattle’s new expensive system. There are budget busting high tech ways of doing it or the cheap ways. Guess which way the heads of traffic engineering like to go?

It’s simple, low tech, not expensive and works great. The rest is greed.

FtG aka GLP

4

Metropolitan Detroit has had timed lights since the mid 60s, at the latest. (They were already established before I got a license.) I was shocked when I moved to Cleveland and discovered that they didn’t even understand the concept.

Timed lights are not a panacea. If a road has too many “race to the next light” idiots on it, they will find a way to jam up traffic, anyway. However, under normal conditions (and if/when the idiots learn that they will spend more time in motion if they flow with traffic instead of racing to the next red), the timed lights allow traffic to flow more smoothly and, actually, more cars get across town faster.

5

I wonder how that would work in a city like Boston, where there aren’t exactly long, straight roads with reguler intersections. Actually, I’ve heard Huntington Ave. is timed for 20 mph, but that you can also hit all greens if you travel at 80 mph.

Timing is probably easiest for long busy roads that intersect several side streets. When you have intersections of major roads, it becomes much more challenging, thus city layout and traffic patterns could have a lot to do with the expense of such systems.

Since I know Boston, I’ll use Kenmore Square as an example. It’s got pretty much everything that would make timing lights more difficult. Basically, you’ve got two major roads (Commonwealth and Beacon) running almost parallel, and this is where they happen to cross. There’s another major road (Brookline) that comes in at a right angle to these two and ends there. There are pedestrians going every which way (not helped by the presence of a subway stop on an island in the middle of the intersection, which the endpoint of several bus lines). And Fenway Park is nearby, causing vastly different traffic patterns every once in a while.

Picture
Map

(last link will probably require manually removing any spaces vBulletin sticks in automatically)

Anyways, there is no way that traffic can flow through unimpeded. This will then require timing the lights on Beacon and Commonwealth heading away in both directions by what the ligts in Kenmore Square are doing. Enough of these sort of kinks in the city’s traffic pattern, that will bring to a screeching halt any improvements made by timing the lights in other areas, and perhaps you can start to appreciate the difficulty and expense of a citywide timing program.

If you aren’t convinced, I could continue, perhaps using Mass Ave. as an example of a major road that crosses several other major roads in rapid succession. And toss in some analysis of how knots in traffic move backward along a road without really shrinking. It’s really only recently that mankind has had the technology to begin to understand how traffic patterns in a large city develop.

6

Try Atlanta in 2001. Same arguements, same issues, and it’s still extremely rare to find lights like this. I was actually listening a discusion on talk radio yesterday about this subject. They called them “smart signals” and “dumb signals”.

There are roads in Atlanta where this would make sense-Peachtree Industrial, Ashford-Dunwoody, Peachtree-Dunwoody, etc. Instead, most of these lights are on timers, so that you sit there at 3AM if you’re coming from the ‘wrong’ direction.

7

Columbia, SC isn’t a terribly large city, but lights are synchronized on some of the larger roads and it works very well. However, if you run that first yellow light, the next ten are going to be yellow too. It seems to work the best when the roads are heavily trafficked but not necessarily at peak rush hours, when the number of cars on the road is going to slow people down regardless. Atlanta, where I live now, could definately benefit from it. As I understand it, you can’t synchronize every road in a downtown area, but you can synchronize paralell roads or certain high-traffic corridors. I’d like to volunteer Ponce de Leon and Peachtree for a start.

For Columbia natives, I’m thinking mostly of Gervais, where you can get from Main all the way to Millwood without stopping sometimes if you hit the light right.

8

I don’t have a car right now, but unfortunatley I do have to catch the bus. I often have to walk around downtown (Edmonton, Alberta, Canada), and I don’t know if it’s just me, but although the traffic lights seem somewhat synchronized for cars, it seems like it works for pedestrians. I’ve noticed that alone many streets if you walk at a “normal” pace (not speed walking, but fairly brisk pace) that the lights will always change in my favor right when I get to the crosswalk. Do city planners take pedestrians into account when planning traffic light?

9

I lived in Portsmouth, OH in the late seventies and early eighties. Unlike many larger metro areas, Portsmouth is cramped by geological features (two large rivers and tall hills, some would say small mountains) and thus most traffic uses US 23 (N-S) and US 52 (E-W).

Until about 1984 or so, the lights on both main drags were synchronized so that traffic could flow continuously at around 32-33 mph, just under the 35 mph speed limit. It worked incredibly well on these “pipeline” roads, especially where the traffic was separated, e.g. most of US 52 had the eastbound traffic on a different street from the westbound, separated by a short city block.

When city planners (a phrase generally believed to be an oxymoron in P-town, emphasis on the moron part) activated a “high-tech” computer-controlled traffic system in the mid-eighties, the traffic pattern went right down the toilet, literally with the flick of a switch.

I guess my point is that timing, or synchronizing, traffic lights can be very effective under the right circumstances. In larger cities with less-constrained traffic, however, managing traffic flow is much more problematic, with numerous arteries criss-crossing and buses and cabs entering the mix.

As for expense, simple synchronization of lights on arterial streets is relatively cheap, compared to the cost of programming and maintenance of fancier systems.

Finally, NO system of controlling traffic lights will compensate for poor planning. One of the best examples I can think of is Polaris Parkway on the north side of Columbus. When the road was built just a few years ago, not much of anybody used it because it wound through corn and soybean fields and didn’t really go where anyone wanted to go. Now, after nearly a decade of unimpeded – and largely unplanned and uncoordinated – residential and commercial development, Polaris IS where hundreds of thousands of people want to go every day. Last year, I lived in an apartment just off the parkway, and I had to travel 1.6 miles east to get to I-71; during certain times of the day, that trek can easily involve 30 minutes or more of sitting in wall-to-wall, creeping, bumper-to-bumper traffic. This despite an ongoing program of adding computer-controlled traffic lights. But since the backed-up I-71 on-ramp is the real bottleneck, the lights have little effect, and I doubt if the traffic pattern would change much if they were all removed. Planners (if there were any) failed to consider the effect of all that development, and the associated massive increase in traffic volume, on I-71 itself, which was already overloaded. Similarly, formerly rural county roads in the vicinity, which now have become feeders to new residential mega-developments, have become clogged with commuters who sit in line for fifteen or twenty minutes at every four-way stop intersection.

Unregulated suburban sprawl can be an ugly thing, and no method of controlling traffic lights is a sure cure.

10

In NYC there is a slight bias in traffic light sychonization towards the bigger streets. Because of heavy volume, the green light works for example on an eight-block stretch in Queens Blvd, or a nine-blocker along 5th Avenue in Manhattan. However there are some anomalies, such as Rockaway Parkway in Brooklyn, between Farragut Ave. and Flatlands Avenue. There is absolutely no coordination there among the 5 lights; as a result one can spend 20 minutes going and stopping there.

11

I live in Atlanta (10th street area) and I think that the lights here are in someway coordinated with each other. The reason I believe this is because whenever we get a T’strorm, the whole strip of lights goes down (they just flash yellow). I’m envisioning that what’s causing this is that somehow the “link” between lights goes down. Anyway this causes absolute utter mayhem. I can’t figure out why these damn things are so sensitive. If it is indeed the link that goes down it would seem like a simple task to install an electronic device that can 1) determine if the link is down and 2) if it is down revert back to a simple timing mechanism. The damn things got power, what the problem? Why does all of midtown need to be paralyzed ever time it rains?

So this might be a down side to synchronized lights, even though it seems ridiculously easy to fix.