I believe we have the potential to eliminate a major fraction of traffic congestion in the near future, using technology that exists today which will be cheap in the future. The method has been outlined by myself and others in the past, but here I offer an alternate way to explain it which may help crystallize it in people's minds.

Today many people drive almost all the time guided by their smartphone, using navigation apps like Google Maps, Apple Maps or Waze (now owned by Google.) Many have come to drive as though they were a robot under the command of the app, trusting and obeying it at every turn. Tools like these apps are even causing controversy, because in the hunt for the quickest trip, they are often finding creative routes that bypass congested major roads for local streets that used to be lightly used.

Put simply, the answer to traffic congestion might be, "What if you, by law, had to obey your navigation app at rush hour?" To be more specific, what if the cities and towns that own the streets handed out reservations for routes on those streets to you via those apps, and your navigation app directed you down them? And what if the cities made sure there were never more cars put on a piece of road than it had capacity to handle? (The city would not literally run Waze, it would hand out route reservations to it, and Waze would still do the UI and be a private company.)

The value is huge. Estimates suggest congestion costs around 160 billion dollars per year in the USA, including 3 billion gallons of fuel and 42 hours of time for every driver. Roughly quadruple that for the world.

Road metering actually works

This approach would exploit one principle in road management that's been most effective in reducing congestion, namely road metering. The majority of traffic congestion is caused, no surprise, by excess traffic -- more cars trying to use a stretch of road than it has the capacity to handle. There are other things that cause congestion -- accidents, gridlock and irrational driver behaviour, but even these only cause traffic jams when the road is near or over capacity.

Today, in many cities, highway metering is keeping the highways flowing far better than they used to. When highways stall, the metering lights stop cars from entering the freeway as fast as they want. You get frustrated waiting at the metering light but the reward is you eventually get on a freeway that's not as badly overloaded.

Another type of metering is called congestion pricing. Pioneered in Singapore, these systems place a toll on driving in the most congested areas, typically the downtown cores at rush hour. They are also used in London, Milan, Stockholm and some smaller towns, but have never caught on in many other areas for political reasons. Congestion charging can easily be viewed as allocating the roads to the rich when they were paid for by everybody's taxes.

A third successful metering system is the High-occupancy toll lane. HOT lanes take carpool lanes that are being underutilized, and let drivers pay a market-based price to use them solo. The price is set to bring in just enough solo drivers to avoid wasting the spare capacity of the lane without overloading it. Taking those solo drivers out of the other lanes improves their flow as well. While not every city will admit it, carpool lanes themselves have not been a success. 90% of the carpools in them are families or others who would have carpooled anyway. The 10% "induced" carpools are great, but if the carpool lane only runs at 50% capacity, it ends up causing more congestion than it saves. HOT is a metering system that fixes that problem.

Metering works, but it's only used on freeways and a few downtown cores. To spread it to the rest of the city, the smartphone is the answer. In many cities, smartphone penetration is already extremely high, and it's forecast to get well above 90% by around 2020 in the USA. It becomes practical soon to expect everybody to have a smartphone and data plan, or even to consider simply subsidizing such a phone to everybody who does not have one. When you consider the hundreds of billions of dollars congestion is calculated to cost, the price of this subsidy is negligible.

Today, your navigation app looks at traffic data (often provided by other drivers running the app driving all the roads) and finds you the fastest route to your destination. The coordination is emergent rather than explicit -- a lot of other phones report they are taking one road and the going is slow, so your phone suggests you take another. Even without being universal, this is balancing traffic on the roads. The side streets which see extra traffic are doing their job better, though the people who live on them don't like it, pushing the idea that they have some ownership rights over those roads and they should not be used by non-local traffic. At the same time, we have come to understand we actually have a lot of road capacity which we don't use because there is no way to coordinate it.

In a metered world, your app doesn't just find a fast route, it would reserve a "slot" on it within a system run by the city or other road authority. A slot allows you to drive that route over a rough window of time. For example, it might reserve a slot for you to drive a particular mile of highway between 8:20 and 8:25am, and a slot to drive the next section between 8:22 and 8:27. If you've used tools like Waze, you have probably already become amazed at how good they are at predicting your arrival time and when you will be on every stretch of road.

The city would hand out these slots, and quite simply not hand out more slots on a road segment than it can handle. A typical freeway lane handles around 2,000 cars/hour in good flow -- around one every 2 seconds. For this approach, after the reservation coordinator has handed out a number just below that many slots, it hands out no more, and instead hands out slots on other roads. The other routes are often longer or slower, but they are almost guaranteed to be uncongested and so quite desirable compared to what we have today.

Allocating the slots

To make this work, there are a few problems that need to be solved:

1. How does the city hand out routes on its roads to people in a way that not only is efficient and fair and beneficial, but seems that way, and can get political approval?
2. How can we be sure everybody, including visitors, has a working GPS phone with power and data plan, or a way to use this without those tools?
3. How do we handle the many exceptions people have, with emergencies and sudden detours and stops in a way that's simple and rarely gets in your way?
4. Preserving privacy and other basic rights.

The first hard problem is that there will be 3,000 people who want a slot on a highway that only has the capacity for 2,000. How do we decide who gets one, and who has to take another route? That's not an easy problem, but it's not hard to do better than what we have today. Today, all 3,000 try to get on that road, and it collapses to stop-and-go traffic. Worse, once it becomes stop and go, its capacity reduces even further, dropping down to 1,200 an hour or worse. That heavy traffic pushes people onto other routes, or they sit and wait. Everybody loses. Today, their phone app helps them find another route. In the past, it was the traffic helicopter, or just the knowledge that commuters garner of what routes to avoid.

Markets

As these ideas are new, we don't know the best ways to allocate the slots. One of the most obvious ones is money -- drivers bid, and the top bidders get the fastest routes. Markets are powerful tools, and if not for the political problem that this makes the best roads mainly for the wealthy or very hurried, this would probably be the best solution. In addition, it would help pay for the roads, which is no small thing.

Lottery

A possible non-monetary method is a lottery. That means some days you win and get the fast route, and some days you don't. It's still a lot better than today, when everybody loses and gets the slow route, especially in some cities.

Winning and losing may also mean being allocated a better or worse start time. This only works when people think about planning their trip in advance, which is reasonable for things like the morning commute. This would allow you to know when your slot is the night before your commute, if you are able to plan ahead.

Imagine that you need to be at work at 9am, and the trip takes 30 minutes in good traffic, but in rush hour, it takes anywhere from 45 minutes to an hour. Right now, you just have to plan to leave at 8am to be sure, and you usually get in by 8:45 and sometimes 9. In the app world, when you win, you would get told, "You can leave at 8:30 tomorrow morning, and get there at 9, so sleep in." If you "lose" you are told you will leave at 8am, but get there at 8:30. Once again, everybody wins compared to what we have now -- some people just win more.

When demand is very high, or if you wait until your departure time to request a route, you might get told there is no route that can make it. You're going to be late -- as is often the case with traffic today, but you'll know it a bit sooner. You may be offered alternatives that will not make you as late, such as a seat in a carpool or a portion of the trip on a train. (You'll get to and from that train with robotaxis or services like Uber.)

Policies for priority

The city could give preference to certain vehicles, giving them either lower prices, or assured wins in the lottery. These could include:

• Transit vehicles, vans and sufficiently full carpools. (This would replace the carpool lane, in fact.)
• Taxi services (which don't reduce congestion but do eliminate parking and circling to find it.)
• Low emission vehicles.
• The mayor's limo. Just kidding -- at least I hope so.
• People having an emergency and using one of a limited set of "silver bullets" they get every month to get priority.
• Those who lost the lottery too much in recent times.

In a world where those who carpool or ride in small electric cars get guaranteed fast commutes at the most popular times, and those who want to ride solo in a Hummer have to take alternate routes, what sort of vehicles are we likely to see on the road more?

This approach also solves one of the greatest dilemmas that road planners have, known as [[w:induced demand]. It's often noticed that after an expensive project expands a freeway or even builds a new one, the reduction in congestion only lasts a modest amount of time. Soon everybody starts rerouting to the new road, and they even start building more houses in places that use it because of the nice commute. Soon it's just as congested as the old roads. With metering, you never allow more cars on the road than it can handle. Roads will induce demand, but never more than they can take.

The city can also set policy about what roads get the traffic. If the city decides to not hand out too many slots for commuters on quiet residential streets with political donors living on them, it can do that. There will be a political battle between the local users of those streets and the fact that the city can use them to add new capacity to the commute network effectively for free, saving the broader tax base a fortune.

It is worth noting this would reduce the need for things like speed bumps and other forms of traffic calming, which nobody likes. If a city blocks or limits commuter use of non-arterial streets, there may be less need for traffic calming, though there may still be a desire to slow down even the locals. Things like Portugal's velocidade controlada lights are a better idea.

Accidents

There is interesting potential to also improve what happens after accidents or other surprises. Of course, these apps could report accidents immediately, and the system could begin immediately rerouting traffic approaching the accident -- as we ask our mobile apps to do already. There is the problem of who gets to keep on the road and who gets rerouted. This could involve money (this might be politically more acceptable for special situations) or another lottery. The lottery could reward all the things already described, or it could even include factors like a demonstrated ability to not rubberneck and stay safe. Robocars of course would be great at that. Instead of money, the city could also offer rewards to those who accept a delay, like extra silver bullets or assured lottery wins in future. Some slop to handle accidents would be built into the system, but unusual events would make people late, but not as late as they make them today.

How to make this work?

The cheapest way to do this would be to have the phone enforce the route -- it knows where you are and can see if you divert from your reserved route. This approach has many problems, but the biggest one is that our phones must work for us, not against us. If we try to make them work against us, people will quickly hack them to stop that, and then the phones will have to fight that and it's a battle which nobody wins. In addition, this (and many other methods) have some serious privacy problems.

A better option could be random enforcement. Randomly located cameras or transponders could look at cars going past. If your car goes down a street where it doesn't have a slot it may get photographed and you will get a ticket. To protect privacy, the law should require that all other records are erased as soon as the slot has passed. To do an even better job, it may be possible to design protocols so that your phone can be pinged over bluetooth or a similar protocol, and it can provide credentials that show it has a reservation for the road it's on. If it can't, a photo is taken and a fine issued.

Another option is to use rewards instead of punishment. Those who agree to obey the system get perks, like access to special lanes, parking, bridges, licence fee discounts, parking or more. Ideally an irresistible set of perks would get almost everybody into the system. Note that a growing proportion of drivers are already obeying navigation tools simply because they promise to find the fastest route.

Being flexible

People are not automatons, however. They need to be able to drive without planning, or deal with surprise situations. They need to be able to make mistakes, missing turns. They need to be able to make unplanned stops. Outside of peak times, there is plenty of capacity to handle that, but at rush hour we would want to plan to tolerate a reasonable amount, but not have people routinely drive outside their reservation.

To help with that, every driver would get some number of "silver bullets" that they could use when they need to break the rules. You could use one of your bullets to get a fastest route, or change a route. To make an emergency trip or an unplanned or different than expected stop. To not make a trip that you reserved, since there will also be a penalty for that. Everybody should get enough bullets to make sure they don't have to worry too much about mistakes and surprises, but not enough to abuse. We might give more silver bullets to parents of young children or others who are likely to have surprises. The number can be fine tuned with time.

This system will also have some slop built in. If you miss your window by a small amount, you probably won't get a ticket. You'll get a warning, perhaps, and try to do better. Of course if traffic causes everybody to be delayed, or go faster than expected, the system will know that and adjust routes and not penalize.

People would of course get special access to their own local roads. You won't get barred from driving the streets close to your house or office, though a longer trip might be denied on some roads.

The system would not even apply off-peak. Your phone will know. It might be nice if there were a way to activate it during unusual situations as well, such as storms or traffic caused by major accidents or other surprises. Here, phones could wake up and alert people and request routes, but the routes might be only advisory unless people agree to them (possibly for a reward like more silver bullets.) That's because some people may not have their phone on when off peak. Of course, car computers with this function would always receive the word.

There may be roads in central districts that are always congested (or which are extra congested at the lunch peak) which merit the use of this system all day.

Not everybody has a smartphone -- yet, or always

This is true, but may not be true for long. Pretty much all phones sold before too long will have smartphone abilities. More to the point, eliminating congestion is so hugely valuable, that it's easy to justify subsidizing smartphones that can do this (and perhaps little else) to those who can't afford or don't want a smartphone. In addition, providing a free data plan good for this and nothing else is a quite reasonable thing a city or country could negotiate with providers.

Of course, phones are lost, data plans max out, phones break and batteries die. The batteries should not be a big issue as long as the car has a charger or a backup battery, but you want backup plans for any situation. The system would work from any computer or phone, letting you print out your route or giving you an easy to remember route that you can jot on paper. And finally, you could use a silver bullet to drive without routing, using any computer or voice phone you can get your hands on to declare this.

While this is something better to have in a phone, many cars would surely implement this service in their car infotainment systems. I also expect that many people will keep one of their old phones in their car, ready to boot up and do the job if their phone fails. (Again, the data plan usable only for this will be free for your old phone.)

Visitors to town who can't download the smartphone app could rent (or even be given, with a deposit) phones with plans at various stores on the way in and out of town. This is already done in many cities that have special electronic tolling systems. And yes, visitors could be given a bit of forgiveness as well. Their out-of-town licence plates could be given a pass on their first few days in town.

Much simpler approaches

Some research suggests that many of the benefits can be attained simply by handing out departure times, not whole routes. We have good ideas of what routes people take, and how that changes with increased traffic, so it may be sufficient to meter by telling people when they leave but little else. This is obviously much easier for people to adhere to and offers a much greater sense of freedom to drivers. Most people would still rely on navigation systems in their phones anyway, and they distribute traffic over the road network already.

A key challenge is enforcement. If a cordon camera detects a vehicle that has left at a different time than is scheduled, you need a solid case to issue a ticket. To do this well you need an unacceptable amount of surveillance -- either lots of cameras so that one near the house catches a person leaving outside their allocated slot, or very orwellian monitoring right in the car. If you catch them late in the drive there can always be excuses as to how they left on time but some delay arose. (They could be required to register an exception when there is such a delay.) Traffic data is now so good that they could not fabricate a story about heavy traffic.

The problem of popular roads getting congested still remains. While people will go to alternate routes if their app tells them they are faster, otherwise such a system has much less power to push people to nice but slightly longer alternate routes in advance.

Other exceptions

I noted above that this system gives cities tremendous power to offer preferential treatment to some vehicles, in particular multi-person vehicles and efficient, low emissions vehicles. This has been tried with carpool lanes, but that approach wasn't enough. Managed traffic, with no special lanes, can do a lot more.

Here are just a few things that could get rewarded:

• The more people in the carpool, the more reward. A 4-pool can get better routing than a 2-pool.
• You can insist that carpool be "real," which is to say contain multiple (potential) car owners from different addresses, and give fewer points to couples riding together, or parents with a kid, who get carpool rights today even though they don't actually take a car off the road.
• You could reward low-emission vehicles, or even calculate the emissions per person to give super rewards to 4 people riding an electric car.
• Of course public transit vehicles and private ones (vanpools, etc.) could get very high reward.
• People who ride transit could forward an electronic transit receipt to get more commute points. This would encourage people to mix transit with car commuting, since if they drive every day they get poor routes, but if they drive only 3 days/week, perhaps they get better routes those 3 days. Telecommuting could also be rewarded.
• You could go even further and take away points from big gas-guzzler personal trucks with solo drivers.
• Moving into dangerous abuse territory, cities could award commute priority points for things other than efficient road use; they could become a valuable urban currency. I call this dangerous because the temptation is high to do this and it would detract from the goal of improving traffic.

Carpooling would require all poolers to register as in the pool. Registering in the pool means you are not driving your car on this trip, and you must have a car or a carpooler certificate (given also to those who declare they could own a car but decided not to because of the ability to carpool.) AI tools in the enforcement cameras would confirm the car appeared to have the number of occupants promised -- this is now technically fairly feasible, and humans can inspect images that confuse the AI. This is how HOT lane enforcement is done today. One could imagine fancy tools where the carpoolers send radio signals at the enforcement points, but for now I want to avoid that.

Economics

Charging people for use of the roads is politically challenging, but an interesting concept from the electric utility world offers one solution. Power lines are not unlike highway lanes, and during peak load times, there is not enough capacity for all. In exchange for lower electricity rates, some companies agree they can be shut off during overloads. It could be possible, when charging road or vehicle taxes, to offer a lower rate, if the car owner volunteers that from time to time, they might be asked to take an alternate route, even if they already won a good one. (They would get a few emergency exceptions for when their travel is critical, but if not in a hurry, they could pause or reroute and take a bit more time.)

Too much control (and other issues)

In some ways, this system might give cities too much control over the roads. The temptation to meet political goals might well end up corrupted or abused. Mayors, city employees or influential parties might get more access to the roads than ordinary folk. The same interests that put speed bumps and traffic calming would go hog wild for the chance to get all those "bad people" off "their" roads. In spite of all efforts, the rich and powerful will find some ways to cheat or bias the system. Cities desperate for tax revenue, finding little solace in existing taxes on cars and gasoline, might love a new opportunity. Fads of public planning could turn into reality very quickly.

These systems generally require the state or national agency which licences cars if you want to fine cars from outside your city. As such, the larger governments will be the one setting the main policies and settling political battles.

Other road charging systems have been subverted in the past. Some places allow only cars with odd licence plates to drive odd numbered weekdays, and vice versa. The rich just make sure to buy two cars, one of each parity. That doesn't work here, as long as not using a slot after requesting it comes with a cost. The system would need to adapt to these and other hacks.

This is one of several issues that need more exploration. Related to this is the danger to privacy. Without care, this becomes a way to track and control every drive in the city, possibly every ride. Some other issues include:

• While most commuters have schedules of when they must be somewhere, there are those who need more flexibility. We want was to give it to them, but here money might be more acceptable politically
• As noted, people will figure ways to try to cheat this, and countermeasures that don't destroy privacy are needed
• This sort of system precludes significant speeding, in that you can't arrive way too early for your reservation slot. This may tempt governments into using it as a tool to rigidly enforce speed limits outside of rush hour, which is a big change in the dynamic. (During rush hour speed limits are usually not meaningful.)
• Any centralized system has a risk of failure. Of course, the "failure mode" of this system is the world we drive in every day today, but once we got used to a well working system of uncongested roads, the reality is that shutting the system off would cause worse traffic than we have now. Absent failure of the mobile data network, the private apps would still do their best to guide drivers, but that would not be enough.
• No doubt more will come up in the comments

New infrastructure

Such complete control over the road use offers the chance for much better use of existing infrastructure. It becomes possible in time to do things like redirect roads to be one-way in the peak direction, even before robocars. The lack of congestion could seriously increase capacity as well. In time, though, demand grows, and too many people can't get quick routes where they are going, and you want new infrastructure.

As noted above, this solves the induced demand problem of building new roads, but it also lets us get a lot more out of our roads. In the extreme, a city could mandate very heavy carpooling, vanpooling and bus riding. The inconveniences of such pooling -- which will get less and less with smartphone technology, high ridership, transfer points, Uber style services and eventually robocars -- would be easily compensated for by that predictable and uncongested commute. The reality is that our roads have immense capacity if you fill most of the seats. We're talking 3 times more capacity just filling the car seats and much more if you fill vans and buses. That's far greater than the capacity of any transit system, and it's free.

On to robocars

This proposal is designed for human drivers, but robocars will be even better at it. They will have fewer accidents, drive in very rational manners and reliably understand and follow directions. They will allow parking lanes to be cleared and converted to traffic lanes, and roads to be temporarily converted to one way in the peak direction. They will make pooling much more pleasant and be more predictable in their travel times. They will even let people switch vehicles, allowing somebody in a solo vehicle to switch to pooling to help when traffic gets too thick.

A world with minimal congestion is a marvelous robocar world. It's a world of short, predictable travel times between places. It's a world where it's very easy to combine people together when they are going the same way to make transportation efficient and cheap. Visions like the neighbourhood elevator I described for smooth medium density living become possible. It permits the ideal city that mixes walking, cycling and short convenient electric car trips that put an entire city of people, jobs, shops, recreation and more at your fingertips -- most of what people like from dense cities, without many of the issues people don't like about density. This does not mean nothing goes wrong, but it's much closer to an urban utopia than has been possible before.

The Connected Car?

My regular readers will know I am a general skeptic of "connected car" plans, yet this is an example of one. What makes it different?

• The only connection needed is getting a smartphone into every car, something that's already happening. That's very different from plans that require new gear built into every car.
• The connection is over the mobile data networks, which already exist and are getting better. There are no new protocols or need for line-of-sight communications or extra infrastructure.
• In theory, each city can have a different system if it wants, in fact multiple bordering towns can even have their own reservation systems as long as the navigation apps know how to deal with that. So there is not nearly as much need for standardization -- and much more room for innovation.
• Reservation slots will be minutes long, so special real-time protocols are not required.
• The connection is to the phone, not the car, or if in the car, to an isolated infotainment section, so there are not the security risks of having a connection to safety related systems. Robocars will require that connection, but they need it anyway since they still want to do traffic based navigation like everybody else.
• If transponders are used, they also can be isolated from all safety systems.

Much simpler -- allocating departure time

Others have proposed much simpler plans than this, simply allocating departure times for people based on their commute. Given knowledge of a commute, there are really only a limited set of roads a person is likely to take, and so you can manage road space to some degree just by making some people leave earlier or later. In addition, if you did that, most people would use tools like Waze, but it would not be compulsory to take their routes. They would balance traffic somewhat, though.

(Photos from wikimedia commons, under GDPL)