Why don't red lights function as alternating stop signs?

My son asked me this question the other day and I don’t have an answer. (Perhaps it belongs in IMHO, but I’m guessing that traffic issues are studied enough such that the answer should be known. Perhaps not.)

His idea is that a guy facing a red light should have the same rules as a guy facing a stop sign (or blinking red light). Come to a full stop. If no parallel traffic, then proceed. The driver from the parallel road has the right-of-way. But the actual rules are of course that a driver cannot proceed through a red light regardless of whether there’s any traffic at all from the other direction. Why is that?

I’m guessing that red lights are generally installed at intersections where it’s relatively uncommon for there to be no traffic from the other direction. But this is very far from uniformly the case, and especially at off-peak hours it’s very common for cars to sit waiting for the light to turn green with nothing at all from the other direction. This seems enormously inefficient.

I can dream up various scenarios where allowing this could cause an accident. (Perhaps the people will misjudge how far away the traffic is? Perhaps the second car will be tempted to proceed through without coming to a complete stop?) But all seem very far-fetched.

I think your guess was right, and that the off-hours inefficiency is outweighed by the regular-hours safety.

Not at all far-fetched. I see exactly this happen here in Panama all the time.

I don’t know how common this is in the US, but at nights and Sundays at some intersections with signals they put a flashing yellow light on the street with the most traffic (which indicates proceed with caution) and a flashing red light on the cross street with less traffic (which is intended to function as a stop sign - you can proceed after stopping if there is no traffic).

The intersection by my apartment building has a major street with two lanes in each direction intersecting with another one-way two lane street. Before they installed a signal about 10 years ago there were constant accidents there as people from the side street tried to dash across and beat cars coming on the other street. (This was made worse because the oncoming lane was downhill, so cars were coming faster than expected, and the view from the side street was obscured on that side by a building). I have seen literally dozens of accidents at that intersection.

After the signal was installed, there were almost no accidents at the intersection during the week when the lights operated regularly. But I think they actually increased on Sundays. Part of this was because during regular operation, a flashing yellow light indicates the light is about to turn red, so people speed up to try to beat it. On Sundays, people would mistake the flashing yellow for a light that was about to change and go through the intersection as fast as possible.

Yes, this is well-studied. Several principles are at work.

People want to get where they’re going as fast as possible. You can’t count on them looking out for safety. There are two ways to force them to safety.

One is design. Speed bumps and humps are increasingly popular ways to force cars to slow down. One great idea is this circular bridge in Uruguay, built to force drivers to slow down.

Another is rules. Fear of enforcement is a powerful behavior modifier. Obeying rules is a habit, built up over time and easily disruptable. People already cheat around red lights, a fact that hits headlines when people complain about red light cameras. If a red light were treated as a stop sign, people would stop stopping. Too many would go right through because they’d quickly build up a new habit of going right through. People with green lights would never know whether they were safe driving through an intersection - because they probably wouldn’t be.

I live in a neighborhood where a long stretch of no side streets suddenly becomes several side streets each with a stop sign. People don’t want to believe there’s a stop sign on every corner. Some breeze through the middle one. Some come to a sudden halt. This is in a purely residential neighborhood with an elementary school. Put this behavior onto a major street and the result would be carnage.

America does have intersections where flashing red lights are used during low traffic periods. Around here these are almost exclusively in rural areas where traffic would be extremely light and probably locals who knew the route. Urban areas almost by definition get a heavy use by people who don’t know the area and so haven’t built up a new habit.

In the US, there is the right turn on red rule which is exactly what you describe, but only for right turns (which are quite safe since you only proceed through one lane of the intersecting road).

[emphasis mine] Did you mean perpendicular?

FWIW, I know many many bicyclists who treat stop signs as if they are yield signs and red lights as if they are stop signs and quite a few have proposed that the law be changed to accommodate this (but only for bicycles).

This might start off as “Go if there is no traffic,” but this would rapidly turn into “Go if you feel like it.” You are basically asking each individual to decide if traffic is far enough away that they can proceed safely.

The intent might be to help people along when there’s no traffic whatsoever, but how would you enforce that? What if there was traffic, but it was really far away? Or if you just didn’t see it? If I have a green light, do I have to second-guess whether the person at the intersection might go if he thinks he can “get away with it?”

It might seem reasonable when a mature, sober, unhurried driver is stuck at a light on a deserted stretch of road. And we’ve all been there. But half the drivers out there are some combination of immature, angry, distracted, late for work, or intoxicated. I’d rather not create more opportunities to add ambiguity to the situation.

Actually, it applies to left turns too. In fact, it’s not about how many lanes you cross. It’s about whether you cross any lanes where the traffic is going the opposite way from where you are going.

Scenario #1: You’re going north on a two lane road (one lane north, one lane south). You meet a traffic light at an east-west two lane road. You are allowed to turn right on red. Easy.

Scenario #2: You’re going north on a two lane road. You meet a traffic light on a one-way two lane road going west. You are allowed to turn LEFT on red into the left-most lane.

Scenario #3: You’re going north on a four lane road (two lanes north, two lanes south). You meet a traffic light on a four lane running east-west (two lanes east, two lanes west). You’re in the left of the two north lanes. You are allowed to turn right on red into the left east-bound lane. Simultaneously, the car on your right (in the right northbound lane) can turn right into the right east-bound lane. Neither of you crosses a westbound lane, so it’s legal. Both of you can proceed through the red light.

Of course, you still have to stop first, and yield to any traffic in the lanes you are entering or crossing.

When I was young most street light switched to blinking lights at night. Blinking yellow on the main street and blinking red for the side street. Too many accidents over the years put a stop to this practice.

I do not believe you are accurate in your description of Scenario #2. If you are northbound on a one-way street, in the left lane, then you can turn left into the one-way westbound. I do not believe any state allows you to turn on a red across oncoming traffic lanes. :dubious:

Given how many people are already whizzing through red lights (not yellow), I shudder to think of it.


Sorry about that. :frowning:

But the thing is that it works exactly like that with stop signs.

Oregon does.

Notice it says nothing about whether the street you are on is one-way or two-way. It only says you may turn left or right if the street you’re turning onto is one-way.

There are two major streets in Eugene that are one-way. West 7th Ave runs one-way east and West 6th Ave runs one-way west. If you’re between 6th and 7th, on one of the many north-south cross streets (almost all of which are two-way), you can make a left on red. For example, going north on Polk street (two-way), turning left onto West 6th Ave (one way), you may turn left on red. I have seen cars do this literally thousands of times, often in full view of a police car. I have never seen anyone pulled over for it, let alone ticketed.

Yes, you are turning across a south-bound lane. But there are no cars proceeding south through that intersection because they have a red light on their side as well. They can make a right on red, turning west, at the same time that you make a left turn on red heading west. Neither of you crosses the other person’s lane. And neither of you crosses an east-bound lane.

Every time I’m stuck at a red light and there’s no cross traffic coming at all and I’m frustrated I can’t just go, I wonder how much longer it will be until we have “smart intersections” with cameras and an AI system which can detect that there is no cross traffic coming and decide to just go ahead and change the light.

Sure, but it’s a feature, not a bug, that lights have different rules to stop signs. The decision on whether to use one or the other is based on considerations of traffic flow and road conditions at a each particular intersection.

There are already sensors in the pavement at some intersections. But the most significant step forward will also involve replacing human drivers with AI.

AFAIK, all large cities already use computers to regulate the timing of at least some intersections to accommodate for traffic. That includes timing so that if traffic is flowing at a given speed the succeeding lights on that street will turn (or stay) green to allow for as much forward movement as possible before stopping on major streets.

If you change even one light to magically turn green for you, the effect ripples out in all directions to change the pattern on all side streets and the streets that they cross and the streets that those cross. From the engineer’s pov, providing optimal passage for many cars over a large area is far preferential to giving you a green light. You’re not an ambulance or fire truck. They can legitimately tie up opposing traffic. You can’t, and shouldn’t.

Twenty-odd years ago, when my wife and I were first dating, we’d go up to Green Bay to visit my family. At that time, late at night, the stoplights in Green Bay would go into flashing mode, and that surprised my wife – she’d grown up in suburban Chicago, where the stoplights never did that. “Do they roll up the sidewalks after sunset in this town, too?”

(At least on the major streets, the stoplights in Green Bay now continue normal operation all night.)

Yes. Exactly. That is why we use stop signs, instead of lights. If I want people to proceed at their own discretion, there are other signals used for that purpose.

If you turn a red light into a stop sign, then why bother having lights in the first place?

It’s fairly common in areas where I have lived.

We basically have that now, except that they detect low traffic flow by counting the number of cars that go by instead of a camera and an AI system. Where I live, if you are pulling out of a side road and there hasn’t been much traffic on the main road, the light will almost always turn green for you almost immediately. The light will also be a fairly short cycle. The traffic lights go into this mode at night when traffic is generally light.

There are several different types of traffic sensors. Only the older ones are in the pavement.

The really old-fashioned type were the metal pressure plate. These were literally a steel plate on a spring, attached to a switch. They tended to wear out over time, often had too stiff of a spring to trigger for light vehicles like motorcycles, and were a big bump to drive across, which tore up the road around the switch plate. Most, if not all of them, have been replaced with something better over the years. I haven’t seen one of these since the 1970s or 1980s.

After the pressure plate, most traffic systems went to the underground wire loop. This was by far the most common type of traffic detector for the last several decades. The traffic controller basically measured the inductance of the loop, turning the whole thing into a giant metal detector. I have played around with loop detectors, and you can set their sensitivity so high that they’ll detect the steel in a work boot. They are supposed to be set so that they’ll trigger on a motorcycle but not on a bicycle, but I have run across many that aren’t set properly and won’t detect a motorcycle reliably.

RF detectors mounted up next to the traffic light were somewhat common for a while. The advantage of these is that they were much easier to install than loop detectors, since you didn’t need to dig up the pavement. They are also much easier and cheaper to repair, again because you never need to dig up the pavement. The down side is they aren’t quite as reliable at detecting vehicles as a loop detector.

The newest type is a camera, with some AI of sorts (they aren’t really all that smart though). The camera figures out what a “normal” view should look like given the time of day and the conditions, and detects significant changes in pixels as a vehicle. Again, the idea is that they are cheaper to install and maintain since you don’t have to dig up the pavement, and they are supposed to be more reliable than the RF detectors. One of these near me completely ignores me when I am on a motorcycle though.

Some of the paranoid tin-foil hat folks think that these cameras are recording your every move and it’s a way for the government to spy on everyone. Most of these cameras do not send video anywhere and can’t be used for spying or tracking people.