# What would be the consequence of a traffic light system where the users with green light pay the users with red light?

Traffic lights are mechanisms that control the usage of intersections. I'd like to perform a thought experiment for an alternative mechanism. The basic idea is that the intersection is a shared resource. Therefore, if some people are using it, they need to compensate the people who are prohibited from using it.

In this thought experiment, we still use traffic lights, but they don't have a fixed pre-programmed schedule. Instead, they react in real time to the current situation, in the following way:

Each driver in a road that is coming into an intersection can choose (using some simple, non-distracting device in the car) a certain amount of money that she/he will pay once the car has gone through the intersection. The money will be transferred to all drivers in all blocked roads (using some automatic payment software), distributed evenly among them. Drivers can update the price that they are willing to pay at any time. The light will always be green for the road whose total sum of money (of all drivers) is largest.

I know that the rules of this system were not well-defined. I'm interested in whether this system is reasonable and can be stable, or whether it will cause chaos and misuse. I'm less interested in the technical problems such as how you make sure that all cars have this system installed or how drivers can perform the update of the payment in real time (although you can certainly share your thought on these aspects too).

• Comments are not for extended discussion; this conversation has been moved to chat. – Monty Wild Feb 25 at 20:28
• Doesn't this break down immediately when you think about a smaller road crossing a busy larger road? The smaller road will simply never get a green phase... – fgysin reinstate Monica Mar 18 at 14:18

## Mixing Money and Public Infrastructure always has unseen results that you don't expect

I'm going to put a different take on this, and refer instead to human nature.

The issue with money being mixed with public infrastructure is that systems become exploited in a way that many in government DON'T expect. 2 examples:

• Toll Roads - Private Toll roads in Australia were meant to allow infrastructure to be built using private funds, however charging for the use of the road for profit leads to people finding odd routes through the city to save money, increasing traffic load on suburbs and small arteries. Sydney now has so many choke points throughout single house suburbs that to get to the airport takes hours from the CBD (most people would prefer to save a few dollars and sit in traffic for hours). The preferred Australian method is now PPP (Public private partnership).
• Congestion tax - Jakarta once introduced a congestion tax that meant any car with only 1 person needs to pay a toll. What happened was an entire industry developed where people made a living by standing on the side of the road and charging less than the congestion tax to hitch a fake ride. This developed into thousands of people, taking unnecessary trips, to earn money by people to reduce their tax. Jakarta removed this tax as soon as they realised congestion was increased as a result, not less.

These examples in my view support the notion that public infrastructure should be independent of money and individual self-interest. As soon as this is introduced people start exploiting it.

For instance, should you consider in your bidding system:

• A whole new industry where people drive only to low-traffic points to be blocked simply to earn money, perhaps even paid by others including companies
• People choosing the most convoluted route possible to earn money.
• People intentionally crashing cars to block routes.
• 'Shadow' apps that seek to game the system that people sign up to in order to bias peoples journey to either earn more money or group people together to bid together
• Courier companies, trucking companies, attempting to use low frequency routes to save money, or grouping together into syndicates to take advantage of the system.

These may counter-intuitively have opposite effects, and it would be more ideal if money is removed from your bidding system. My ideal is if an AI is in charge of all traffic lights, it should be possible to optimise all traffic light operations to achieve the goals you want through simulation and constant adjustment, depending on the goals you want to achieve.

• For what it’s worth, “CBD” is not “central business district” to most Americans. I heard that usage for the first time on TV yesterday, and I’m 65 years old. – WGroleau Feb 23 at 16:55
• On the other hand, if you want your story to show an ultra-capitalist dystopia... – user253751 Feb 24 at 11:49
• Side question: What exactly is the difference between PPP and private toll roads in Australia? How does this solve the problem with people avoiding toll roads and jamming "free" roads? – I'm with Monica Apr 22 at 12:22
• @I'mwithMonica PPP is where use of the road is free (public), but the building of the road could be private, the financing for it could be private, or the maintenance is private. This then allows at least a major portion of the project to be based in the private sector and thus take advantage of competitive tendering environments, but without the consequence of the entire endeavour being private (and thus needing to recoup cost to make profit). By making its 'use' free this does not then disproportionately affect the traffic system. – flox Apr 22 at 14:22
• @flox, so in this scenario the government pays the toll for everyone. The private sector still makes a profit, probably. Why else would they do it? - So the only thing actually missing from the equation is the risk for the private party: In the former situation, they don't collect tolls, if they are too high. Now the "toll" is pre-agreed and will be coverd, if anyone uses the road or not? - Seems not so great to me. - But that's a political discussion. Thanks for the clarification! – I'm with Monica Apr 22 at 14:32

While an interesting thought, I can see a few major flaws with this system:

You are never the only one to arrive at an intersection. You will almost always be behind someone. They might not have the same financial status or preferences, and might opt to wait instead. This means you might have to pay not only your share, but also their share to get a green light.

Also, some people might opt to wait at an intersection for an extended period instead, as an easy way to collect some money. They will hold up the people behind them, and this will lead to increased road rage and potentially dangerous situations.

Also, this might be highly ego-dependant as well. I could imagine an insanely rich person driving around assuming every light will be green for them based on the amount they are willing to pay. If this doesn't happen for any reason (an even richer person comes along for example) they might not pay enough attention, and might not stop in time.

• "you might have to pay not only your share, but also their share to get a green light" - this imho is a feature, not a flaw. – Alexander Feb 21 at 17:57
• That rich guy is probably going to collide with an emergency vehicle since they probably always get to go. Added irony if that emergency vehicle is responding to another rich guy hitting an emergency vehicle... – Muuski Feb 21 at 22:14
• @Plutian regarding your second point: don't you think that this situation won't happen since waiting means willing to pay only 0$, which would mean that the other side need to pay just a bit over that, which would mean that the waiting driver doesn't really earn money and therefore is wasting their time waiting? And if it were so easy to make money this way, many people would try and this would make it far less profitable since the payment is distributed among all of them – Lior Feb 21 at 23:23 • @Lior you would be surprised what people do for money, even the smallest amounts. – Plutian Feb 22 at 0:00 • @NotThatGuy it's not the total cost of the lane I'm aiming at, but the mean between the cars. If you have an intersection with 5 cars crossing from two sides, and all pay$10, you will end up with $50 a side. If one guy doesn't pay, the rest in his lane will have to pay his share as well as an increase if they want to go first. – Plutian Feb 22 at 19:55 This system is probably the way of the future with the exception of traffic lights, which will become nonexistent as soon as we only have self driving cars. Automated negotiation of right of way for autonomous driving is a real research subject. Sadly I can't find the video but my university is testing a system where AI driven cars negotiate in some fashion in real time who has the right of way. The negotiation include how much energy they need to spend and how much time they win and loose. A result was that trucks will tend to "pay" more since braking and accelerating costs more for them. So far the system has only been tested on a single intersection with a few self driving cars. But the result is that at high speed negotiations the cars don't stop anymore at all. One will break a little bit to give just enough room for the other to quickly pass through. Not the video I was looking for, but this is the gist of it: Autonomous intersection • Would hate to be a pedestrian in that intersection! – elemtilas Feb 21 at 14:52 • automated, otherwise you can game the system. The 'simple device' becomes extremely complicated but it remains 'non-distracting'. The car has to drive itself but there could be a selector switch for how much you're willing to pay for Traffic signal preemption, which must still be governed by an algorithm to allow EMS to override it. - Speeding is already pay for play, as long as you get less than 3 tickets a year and can afford them; this would just make it official. – Mazura Feb 21 at 20:26 • It's only a matter of time before autonomous vehicles negotiate who to hit in case of an accident depending on who can afford to pay the most. – Bob says reinstate Monica Feb 22 at 19:23 • Sort of related :-) : Long ago a new motorway was being constructed along a gulley in our city. It largely went under existing gulley crossing bridges but at the town end it crossed a major road. There were traffic lights and construction traffic (typically large motor scrapers carrying soil one way) had immediate access and resulted in a red light for road traffic. Our dirt bikes were also able to activate the lights as we rode to and from town along the dirt :-). Fun but embarrassing - many cars queued to allow a dirtbike to pass through. (True story). – Russell McMahon Feb 23 at 11:56 • Minor correction: traffic lights will not become nonexistent as soon as we have self-driving cars, they will become nonexistent as soon as we only have self-driving cars – jla Feb 24 at 5:25 The big problem here is that it will greatly reduce the throughput of intersections. A major part of designing intersections is balancing throughput with latency. A traffic light that never switches maximizes throughput in one direction -- vehicles never need to stop for the light -- but maximizes latency in the other -- vehicles wait forever for their turn to pass through the intersection. As switching frequency increases, latency goes down, but so does throughput, as vehicles need to stop for the light more often. I expect that your bidding system will cause frequent changes of the light. This is great for minimizing wait times, but reduces the total number of vehicles that can pass through. The intersection spends most of its time in the "switching" state when no vehicles can enter, and those that do enter are usually accelerating from a stop, so the average speed is quite low. It will provide little benefit, if any, over a four-way stop. • There is latency in only one direction. As switching increases, latency is introduced in the other direction increasing the average latency. Switch fast enough and the whole system becomes latency because vehicles don't have enough time to pass through the intersection before the other way has a green. – CJ Dennis Feb 23 at 3:39 # It kills one of the main uses of traffic lights One of the best uses of traffic lights over stop signs is to allow intersections of very large (high volume) roads with very small (low volume) roads. If I am the only car at a stop sign intersection with a 3-lane, packed road, I will never get to go. Stoplights fix this problem by forcing the high volume road to stop. Well-programmed stoplights allocate green light time in proportion to the average amount of traffic on each road, so cars on the smaller road may wait a long time, but not forever. However in your system, aside from the mega-rich, there is no way that one car could outbid 30 other cars competing for that intersection, so they would be stuck there forever. ## maybe consider a non-money system that allows hyperinflation Instead of money, what if your system uses "credits", or a "stopped time bank". In the simplest implementation, ignore any kind of bidding for the moment. Whenever you are forced to wait at a traffic light, your account is credited with the number of seconds that you had to wait. If your credit exceeds the summed (or maybe average?) credit of all other cars at the intersection, you receive the right-of-way, and the amount of time is deducted from your account. This would be hyper-inflationary because credit would be multiplied: time is deducted from a single account and added to multiple ones. You could instead deduct the amount of time times the number of drivers at the red to keep relatively constant levels. If you wanted to retain a bidding system, you could possibly bid by the maximum multiplier you are willing to pay. • "there is no way that one car could outbid 30 other cars competing for that intersection, so they would be stuck there forever"...Wrong, your credit idea is built into the system because a person who is trapped at a light is getting paid by those 30 cars and can eventually afford to outbid them. – Muuski Feb 21 at 22:08 • Hyperinflation by definition means the economic model isn't stable. You'd need some kind of dampening factor to keep edge cases from blowing up the whole system. – Chuck Adams Feb 22 at 17:24 • To help with hyperinflation, you could set it to reset daily/weekly etc. – Bob Kerman Feb 24 at 3:23 It will cause chaos. One of the things that traffic lights do is restrict the volume of traffic on the road beyond the signal. There is a counter-intuitive characteristic of traffic (typically on freeways, but a signalled road will exacerbate the problem) that when volume gets to a certain point it goes from free-flowing to stopped, and you can make people arrive at their destinations faster by forcing them to wait before entering, to keep the overall volume below the changeover threshold. Allowing traffic flow to be determined by individual self-interest will result in major routes being completely saturated and immobile, because nobody is going to voluntarily block their own progress, or take a significantly longer route (except for the few weirdos like me). If you instead allowed drivers to bid on their entire route, and used some central control to allow those paying more to travel on lightly used (faster) roads, then you'd have something that would probably work. • The last paragraph sounds a lot like how some cities allow single drivers to pay to use the HOV lane/express lanes on a highway, with prices scaling based on the current traffic level, in an attempt to keep overall general lane traffic down. – Troyen Feb 22 at 1:27 • Okay, so only the 10 highest bidders per minute are allowed to pass through... – user253751 Feb 24 at 17:57 Circular intersection also called "Roundabaouts" or "elipticalbouts". Also this is not a thought expirement. This is Auction experiment. So - how much you are willing to give for a$1. The best profitable option is of course 1 cent. But if two people are participating the best option would be to give 99 cents.
But people don't think this way. They want to gain as much profit as they can while spending as low as they can. So they incremeant with 1-5 cent.
And at certain point they are willing to pay over one dollar just to win.

So when you want to ear money you set the amount you want to pay at one cent. Or none if it's possible. Anyone else with higher amount will pay you. Even when you are not willing to cross the intersection you will just milk all people with "pass = higher than 1 cent".

While you will not spend a dime because you will wait for others, behind you, to pay for green light. And people will think
"I need to give few bucks because the guy ahead is stuck so I just need to overbid the dude on the other side".

In the end the "milkers" will literally earn cents while forcing other to spend dollars and let others earn dollars "Hey, I just got paid $5 becasue I have pass set to 5cents". Blocking the roads. Making millions of loss for everyone. THe way you install the thing is just install it. Make it mandatory. Ever heard about FAP or DPF filters? Mufflers? Lights? Belts. Oh, (said in my best Colombo voice) just one more thing. People who have plots at the intersections could just make a right turning road and just charge people flat rate of 2 cents. • The$1 auction experiment only works that way if the loser also has to pay their bid. – user253751 Feb 24 at 11:49

using some simple, non-distracting device in the car

First I want to address this specifically. It's not possible to not be distracted. That's just not a thing. I'm a driver, and I'll make the bold claim that anybody that says otherwise is either deluded or lying. I've caught myself spacing out trying the turn the radio up, imagine what it'll do to people having to do math on the road.

That said, let's imagine it magically just works. There are still a lot of problems with this idea, because the road is a harsh mistress and there are a lot of variables you have to account for:

• Different roads have different amount of traffic. Small roads could simply never get the right of way because there's not enough people to offset a big 8-lane boulevard.
• Sometimes you have to turn left and cross traffic, so in a standard 4-way intersection you're competing with 3 other streams of cars...
• ... plus pedestrians.
• ... plus public transportation.
• ... plus any lobby group (e.g. taxis, delivery, etc.) that manages to get a special status, either de facto or de jure.
• Emergency vehicles cannot wait.
• And then there's all the ways someone can game the system, including organised crime.

Just figuring out an ideal system (i.e. one where people don't become maniacs and respect the rules) that guarantees everybody can eventually pass within a reasonable time frame without creating undecypherable gridlocks is going to be a big enough headhache.

And if you manage that without it being overtaken by corporations that'll make it worse than broadband in the US (in a nutshell: terrible service, terribler price, terriblest customer service, also don't try to actually compete and offer a better service than us because we'll sue you), in this perfect ideal world, it's still a massively terrible idea.

Why? because it's...

## Straight up inegalitarian

I'm sure we can agree the rich have it good enough that we don't need to give them more power. The problem of your system is simply that movement ceases to become a right and becomes a commodity. That's bad. That's really bad. It's bad because it will accentuate inequalities that already exist and put even more weight on already underprivileged communities.

Some people can't afford a car and have to take a bus. Your system will more than likely jack up the prices of bus passes because the busses need to cross intersections. Some people can barely afford owning a car, but now they'll be unable to afford driving it. Now their mobility is reduced to where the bus takes them, the same busses that already got more expensive. For those that can still afford driving, it means reducing their purchasing power, and it means increasing their commute time.

Your system is going to make the cost of going to the movies become prohibitive for a larger number of people. Same for museums, or libraries, and eventually groceries, delivering mail and packages. But more importantly also just going to work or to school.

Your system doesn't answer to a problem (which already is reason enough to not implement it). Instead, it creates one, it creates a new class of people that can't afford going to work anymore, and another class barely above that can't afford leaving their house except to go to work. It simply creates more poverty and exclusion, and that is really, really, really bad.

In comments, the argument has been made that the money you can earn could offset the cost.

Firstly, you might be getting cents or fractions of a cent for every car that snobs you. That's true. But you are also paying to turn your light green in the end, and you have to factor in the cost of energy spent idling unnecessarily. So I wouldn't necessarily assume the economics of crossing an intersection are beneficial to you, let alone the economics of a complete trip.

But even assuming you make any significant (in the statistical sense, i.e. more than crumbs) amount of money stopped at red lights, that means someone loses. And it won't be just the filthy rich. It could also be someone poorer than you, that has to pay the premium because they can't afford to be late to work again and lose their job. And you won't probably not care about them until it's you that has to make haste and spent all the money you've earned so far to go through.

And that's when you account for the other variable of the equation: time. Time is money, we've all heard that, and in a sense work is the literal proof of that. So what is behind an extra half an hour of commute? It's 30 minutes of a sitter's wage. Or it's 30 minutes you don't have to study. Or it's 30 minutes away from your loved ones. It's little things like getting less sleep or not having time for extracurricular activities.

And here we are again, taking about more poverty and exclusion, which is still really, really, really bad.

• Note: The effect of giving rich people more power might be cancelled out by the effect of giving poor people more money. – user253751 Feb 24 at 17:58
• @user253751 Don't be silly. The rich would never willingly give their money to plebeians. They would just lobby for a special "charitable donation" route so that all the money they pay to get priority ultimately winds up back in their own pockets. :3 – Tezra Feb 24 at 18:09
• @user253751 Except this affects everything that moves on the road, people and goods. So you can imagine the price of groceries goes up, so does the price of hygene products, medication, schools books, and so on. You can also imagine that a blackmarket would develop, meaning crime. The whole thing has far reaching effects. – AmiralPatate Feb 25 at 8:17
• @AmiralPatate Both rich and poor people will pay extra for their groceries, hygiene products, medicine, ... in fact rich people will pay more if they consume more. Remember that absolute price levels don't matter. It doesn't matter whether bread costs \$1 and wages are \$10, or bread costs \$20 and wages are \$200. – user253751 Feb 25 at 10:34
• @user253751 The rich by definition can afford the extra cost. That's why they're rich. There's also a difference between 9 bucks left and 180, unless you assume the price of every good, service and wage inflates at the exact same rate, which doesn't seem realistic. But that's besides the point, and I made an edit to adress the whole "but you can earn money" angle. – AmiralPatate Feb 25 at 13:14

I don't think that SPECIFIC situation works because of the nature of an intersection, but let me state the same type of plan in a slightly different scenario:

On freeways I often encounter a ramp to another freeway that backs up (Sometimes for quite a long way). A common response is for people to get out of the lane and into a faster lane, but then to try to cut back into the slow lane before the ramp (We all know this is the cause of much of the slowdown in the first place, but let's ignore that part for the sake of this discussion).

This is clearly a person who thinks their time is more important than that of everyone else in the lane. Some recently described this action as "stealing 10 seconds of life from each of 30 people in order to give themselves an extra 5 minutes of life"--something you'd expect from a supervillain-style bad guy.

However if everyone in those cars could put a price on letting someone go to the front--then someone willing to pay everyone they are going to slow down could make sense.

I could imagine a system that automatically negotiated how much you had to pay against how fast you wanted to arrive to come up with a small amount of cash that is transferred.

I suppose (as with your intersection example) that NOT using the street at all is the best thing you can do, and you should therefore be paid the most for staying home.

Interesting thought experiment.

• You are already paid for staying home. It is called the price of petrol/gasoline. – user253751 Feb 24 at 11:51

a certain amount of money that she/he will pay once the car has gone through the intersection.

Ok, so I'll bid one million dollars every time I see a blocked intersection down the road, but change the bid to $0 once I'm close enough to make it through the intersection even if the green turned yellow at that moment. Or I could start a VIP business: run a few hundred cars in a loop through all major intersections, so that whenever a car of some of my clients gets to any of those intersections, a nearby driver of my facilitator car would bid a huge sum of money to let the client pass free, and then rescind the bid so that it's never paid. With a few modification I think it could be pretty good. Here are a few things I think need to be adjusted/kept in mind: • other traffic laws must still be obeyed, some one can't just park on a traffic light to collect money • the amount of money you are willing to pay has to go to everyone waiting at the light AND be influenced by the amount of time the light has been red, so a congested traffic light will increasingly expensive to to keep green and a single guy trying to merge into traffic won't be stuck forever(this is important for things like voter finagling by having a few rich people block access to voting areas that will vote against their interests) • use a second-price auction model to encourage people to pay their real valuation It would defiantly be interesting to see how this works out with actual people, some one should make a social experiment or/and game about this • A second-price auction model will affect the income from the$0 queue earners, as if they are the only one in the queue they will only ever be paid 1c per car that passes them. This may be a benefit of this system – Kyyshak Feb 24 at 15:11
• @Kyyshak Like the answer says, a second-price auction encourages people to pay their real valuation. The person who can afford to pay \$10 won't be discouraged from bidding \$10, by the chance that he might have to pay \$10 when \$1 would've been enough, because there is no such chance. – user253751 Mar 2 at 16:38

The solution may be more plausible if you abstracted the money away by one level.

Imagine that every traffic light at an intersection has an automated load-balancing system. It automatically balances the times each light is Green/Red to maximise throughput through the intersection and reduce wait time. It operates mainly on number of cars waiting vs. number of cars going through the intersection. Obviously it would have to be programmed so that single cars waiting on side streets at major intersections and pedestrians still get a chance to cross the road in a reasonable time. This all happens automagically using image recognition software and little GPS/RFID tags in each car to determine who is at the intersection.

Where does the money come in?

Simple - there are multiple tiers of car registration and licensing. When registering your vehicle with the Department of Transport, there is an option to pay an additional annual fee to receive favourable treatment. This isn't an absolute, but for example, maybe the first tier above basic makes your car count as two vehicles for the purposes of load balancing, the next tier three etc. etc.

Emergency vehicles would receive absolute priority, and there would be a hard upper limit on the priority given to private vehicles.

Basically the payment isn't done at the intersection, but as an annual fee.

• "Emergency vehicles would receive absolute priority" - surely if I'm willing to pay more than the value of a human life, I should have priority over emergency vehicles, right? :) – user253751 Feb 24 at 11:53
• To follow the idea to it's dystopian conclusion - Yes; if you're a (b/m)illionaire, and you're willing to pay enough, you can get absolute right of way at traffic lights, even over ambulances. – Chromane Feb 24 at 23:43
• Not even more than the "value of a human life", but more than the other person is willing to pay to save their own life. And since that person is currently incapacitated, the ambulance will have to make a bid on their behalf and bill them for it later. – user253751 Feb 25 at 11:16
• The idea of my suggestion is that instead of on-site bidding, priority is determined before hand by who is willing to pay the larger registration fee for their vehicle. So you'd pay a huge, once-off fee, and have priority over the ambulances all year! – Chromane Feb 27 at 5:57
• Also makes ambulance rides mandatory if you you saved money on your car registration. – user253751 Feb 27 at 16:05

Intersection control is just CPU scheduling in disguise, for which there is ample research already existent. The limited resource (intersection, CPU) is allocated to multiple clients (cars, jobs) in order to maximize utilization of the resource, among other things. There are costs associated with changing jobs (stopping and restarting traffic), there are varying priorities among clients (both self- and system-assigned values), along with escalating priorities if something is forced to wait overlong...

Huge fun!

• Your answer describes the hypothetical situation and does not address its consequences which is the subject of the question. – a4android Feb 22 at 21:35
• This could be developed into a good answer. Maybe add some discussion about how similar CPU scheduling systems work and what effects they have. – Ryan_L Feb 22 at 22:11

# Gridlock

Well, the first problem that comes to mind is gridlock. A lot of math and light coordination goes on to optimize traffic while preventing gridlock, especially in large cities.

# Disenfranchising the poor

The sad fact is this policy clearly benefits the financially well off. This means you could force poor people into a situation where they can't hold a job because "if they drive, they will be late" or "if they walk/bike, they will be sweaty when they get to work".

# Congestion

As it turns out, the best way to minimize road time is for everyone to drive to a random place, and then drive to their destination. While this is a longer path, it makes every part of the network (road) equally used, and prevents congestion. Since your method makes people pay per light, everyone will optimize their route for minimum lights, and thus maximize congestion.

# Crime

Where there is money, there is crime. So all I'll say here is you've just made street lights an active target for theft/abuse. Other answers contain plenty of examples, and even all of those only scratch the surface of what could be done.

• Has anyone been fired for being sweaty because they walked or biked to work? – user253751 Feb 24 at 17:59
• @user253751 If you work in the service sector, yes. They will fire you for far less. – Tezra Feb 24 at 18:05

Traffic flows are very complex. There are fairly simple situations in which adding an additional road can increase journey times compared to the road not existing.

Any good traffic control system does many things, such as times the lights at successive junctions so that (as much as is achievable) drivers reach the next light at green. This keeps traffic flowing, reducing congestion, and keeping drivers happy.

They also balance traffic flowing onto/off main routes.

This system you propose would probably lead to a significantly increased journey time for most if not all drivers.