Curiosity is bliss    Archive    Feed    About    Search

Julien Couvreur's programming blog and more

Traffic light versus stop sign


Quick question to which I could not find an answer: between a traffic light and a stop sign, which is the best for an isolated four way intersection?

My fiancee and I were thinking about this driving tonight, but couldn't come up with a quick analysis.
Some factors that come into play are the traffic distribution/load, distribution of cars going straight versus making a turn, number of lanes and whether the stop lights are smart (with sensors).

Average traffic throughput and emitted pollution are some criteria for the comparison. Another one is the psychological impact on the drivers, but it's harder to quantify.

My guess is that lights are better on a number of aspects but for the price and the space for additional lanes.
Stop signs require everybody to stop, but lights lets some people drive right through under some conditions. Generally, it seems that lights create less stop-and-go (which is inefficient in terms of pollution and delays due to reaction time).

Any thoughts?


but then there is wiring for the stoplights, and a computer system to admin, not to mention digging up the road (which makes a temporary stop sign) to put in the sensors for the lights,... seems much cheaper to do it wyle e coyote style and just throw a stop sign up...
Unless you used a Solar powered system, and some sort of 'headlight sensors' or 'semi large movement' sensors to 'flip the switch' on the lights, or maybe a 'power down' feature when no movement in 300 yards.. But the R&D for that alone is goin to be alot... so it still seems that the stop sign is best..
and from a distant drivers point of view.. a 'stop sign in the middle of bum fuck egypt gives me a chance to take a piss, throw out a lil garbage, and stretch the legs (if there hasnt been anything in like 60+ miles.. may as well.. right?).

Just my two sleepy cents :-D

Posted by: sn0n (July 6, 2005 11:14 PM) ______________________________________

and what about a roundabout ?
nobody can drive through at full speed, but nevertheless it regulates the traffic without dead times, and you need no complicated wiring and sensors, maybe some blinking warning lights...

Posted by: nnoia (July 7, 2005 01:39 AM) ______________________________________

Good point nnoia.
Roundabouts are super popular in France, but for some reason I've seen very few over here in the US.

Posted by: Julien (July 7, 2005 08:33 AM) ______________________________________

Well, cities don't like to buy or maintain stoplights without a good reason. They cost more than stop signs. ;-)

And traffic engineers, these days, don't like to put up obstacles like stop signs without a good reason. The more stop signs somebody has to handle, the less they pay attention to them.

An isolated intersection will always have a choice between two-way and four-way stop signs. Unless traffic levels are approximately equal, two-way is going to be preferred. One street is almost always substantially busier than the other.

The roundabout, though, is an excellent choice for certain high-volume intersections, and it is definitely making "inroads" (groan) in the US. The first one was installed in Vail, CO in 1995, and they're already found in many states. Wisconsin is a recent convert and we now have a handful. (It takes years for something like this to get through the planning and funding hoops.) States like New Jersey and Connecticut, which have old-style "rotaries" (a pre-war roundabout with sub-optimal traffic controls) are converting them to roundabouts. I don't know of that many municipalities that are creating full-size roundabouts -- most of the new ones are on state highways and the like -- but many cities are using "traffic calming" strategies that include mini-roundabouts at some intersections (they install a flowerpot in the middle and force you to go around it to get through). These aren't substantially different from a stop-sign intersection, though.

For more on this than you ever wanted, google "roadgeek". ;-)

Posted by: dan hartung (July 9, 2005 12:28 AM) ______________________________________

Another factor is the speed limit on the roads. If it's in the city and the speed limit is 25 MPH, a 4 way stop is not nearly as big of a deal as it would be on a 55 MPH road.

As you mentioned, the traffic distribution is also important. There's probably a certain level where if they diverge (ie. 20 cars per minute vs. 30 cars per minute) by a certain amount, the lights make more sense.

It's an interesting question, and I bet there are some engineers out there with some awesome tools and equations to figure it out.

Posted by: Dusty (August 2, 2005 08:45 PM) ______________________________________

Roundabouts are pretty popular in Massachusetts too, particularly in the greater Boston area.

One problem though are the "rotary"s as they call them here, is that in the case of multilane traffic, drivers in the outer lane are able to move much faster then in the inner lanes and this tends to create more "jerk" drivers.

But driver attitudes are a different problem I guess. Other than that, I think rotaries or roundabouts are a great way to manage traffic flow automatically and cause less disruptions.

Posted by: Raja (September 6, 2005 09:17 AM) ______________________________________

Here is a research document on roundabouts in USA. It should answer everyone's questions:

Posted by: James Anon (September 6, 2005 04:55 PM)
comments powered by Disqus