A recent newspaper column where people complained about carpool cheats got me thinking -- could cheating actually be a solution to some carpool problems?

For many years, the wisdom was that carpool lanes were helping traffic and the environment, but that wisdom has been changing, and it is now seen that the lanes actually hurt (at least the traffic) in many cases. As such, the new approach is to build "managed lanes" and in particular the High-Occupancy-Toll (HOT) lanes which let solo drivers pay to use the lane. In addition, low emission cars and motorcycles usually get to use the lanes solo.

Why does this help? It turns out that a typical configuration of 3 solo lanes and one carpool lane is performing badly when the carpool lane is well under capacity. The ideal road would have all 4 lanes running just under 100% capacity (which is around 2,000 cars per hour, or 8,000 for the whole road.) At rush hour, however, the lanes often collapse in congestion to stop and go, which can drop as low as 1,300 vehicles/hour.

Carpool approaches suggest that if you have one carpool lane running at less than capacity (and thus congestion free and highly attractive) that you will make people choose to carpool. Each carpool takes a car or two off the road, which is a win for congestion (and the environment.)

Consider one carpool situation, where the carpool lane is running free at 50% of capacity, and the other 3 lanes are at 100% of capacity. You're now moving 7,000 vehicles/hour instead of 8,000, but that would be OK if it's because you took more than 1,000 vehicles off the road.

Unfortunately that's not even remotely true. The vast majority of the carpools on the road are natural carpools that would have happened anyway. Couples or families travelling together. "Kidpools" where in almost all cases no car was taken off the road. The permitted solo drivers in low emission vehicles and motorcycles don't remove cars, but are greener. The number of "induced" carpools -- carpools that were created because of the attractive travel time offered by the carpool lane -- is quite low. Perhaps as low as 10%, but likely not more than 20%. HOV-3 lanes may have more induced carpools.

To make it worse, consider a carpool lane at 70% usage (good) but the 3 other lanes in congestion, and now getting 1,500 vehicles per hour. We've dropped our road to just 5,900 cars per hour. And at 20% induced carpools we only took 280 cars off the road, for a total of 6,180 instead of our ideal of 8,000. There is a zone of congestion where moving another 500 cars from the solo lanes to the carpool lane would relieve the congestion in the solos, and we would get closer to our 8,000.

That's what HOT lanes are about. By charging a fee, they move solo drivers who are willing to pay to use the underutilized carpool lane, and we remove them from the solos, increasing their throughput as well. It's a win-win-win. HOT lanes adjust the price -- if the carpool lane is starting to fill up, the price jacks up. The goal is to keep the carpool lane enough below 100% capacity that it flows smoothly, which is good for flow and also what makes it attractive in the first place to make those induced carpools.

With HOT, you can have 1,000 carpoolers and 900 paying solos and also 200 induced carpools so the lane is now delivering the equivalent of 2,100 vehicles/hour and everybody wins. Letting efficient solos use the lane doesn't involve money, but subsidizes efficient vehicles.

Without HOT, the bizarre conclusion is that cheaters are helping move traffic along. Cheaters only cheat when the carpool lane is going really well -- ie. underutilized -- and the solo lanes are getting congested. Cheaters take some load off the solo lanes and make use of the wasted capacity. They will not cheat if the carpool lane is not beating the solo lanes by a nice margin. If the carpool lane gets overloaded, they are going to leave it -- why risk the ticket?

I should note that I have never, ever deliberately cheated in the carpool lane. (Like most, once or twice I have forgotten what time it was for a minute or two.) I am not trying to justify cheating, and in fact one concern is that some cheaters will read this and imagine they are doing a service. Cheaters are helping the system, but in a completely unfair and inappropriate way.

Legitimizing Cheating

One reason we don't have more HOT lanes, now that people realize that they are better, is that it costs a lot of money to put them in. Part of that money is for infrastructure -- gantries, transponders, signs with prices, enforcement teams, operations teams. The biggest cost comes from the fact that generally people like to make HOT lanes truly separate from the main lanes, with a double line, and entry/exit only allowed at certain points. That means restriping or even new construction.

Many of the world's transit systems work on an honour system. You have to buy a ticket, but nothing checks this. Instead, if you are caught on board without a ticket, you pay a fat fine. The fine is often calculated to balance the enforcement level, so that a regular cheater will be caught enough that it's more expensive to cheat than to buy tickets. But often not a lot more expensive, as it turns out.

What if HOT lanes were the same way? Go ahead and cheat! Install random enforcement stations with cameras, and enforce enough so that any regular "cheater" gets fines which are calculated to collect as much or more money than the tolls.

The obvious flaw here is that this only works for the regular cheater. It's too random, and an occasional lane user (or tourist) would be taking a big gamble, without enough use to balance it out. So we can add payment by cell phone to even things out.

Online payment

Before leaving, or after arriving, tell your phone or browser you will be using or did use the lane. (The reason to do it in advance is you will get a better price.) Your phone can show you the price, and some road signs will display it as well. This gives you a token which includes the time and your licence plate. If you get a fine notice, you can nullify it by providing the token.

(If you don't care about privacy, you could register the licence plate directly. But I do care about privacy.)

This works with minimal new infrastructure. And payment via phone would be set to be cheaper than the average payment you would pay through random fines, so most people would do it. And all this happens with minimal new infrastructure, as long as you don't need to reconfigure the lanes.

Enforcement can involve cameras, which may or may not be recording. You need enough of them so that people don't just briefly switch out of the carpool lane just before coming to a camera, so this has some infrastructure cost. The camera would record the photo of the front seats of your car, and your plate. In isolate carpool lanes this does work better.

This is aimed at places where 2 is a carpool. It means something controversial. Carpoolers must share the front seat. And that means no kidpooling with children small enough to be required to ride in the back seat. Some people will hate that (parents) and some will love it (those who feel that kidpooling is unfair because it almost never causes an induced carpool.) This controversy can be some what mitigated by offering a discount to people who declare they are kidpooling (or better, multi-family kidpooling) with occasional checks.

It's also an issue for Taxis, Uber and people with chauffeurs. Forcing the latter to pay won't bother many people. Taxis can be given special status. Ad-hoc taxis, like Uber, can be told, "hey, just make the ride in the front if you want a free entry." Is that such a big burden? If so, alternate systems can be set up, including requesting a token over the smartphone which can be compared to audited records of fares.

The camera stations could also photograph in through the sides of vehicles. Tinted side windows would not get to be carpools. This is harder than just doing the front, and harder to hide. And there would still be occasional live human observers, to the extent that cost allows.

To avoid risk of people wanting to use phones while driving, we simply allow you to buy a retroactive token within a day of your trip. (You don't learn about your fine for a couple of days.) You could do that on the web, on a smartphone, by text (retroactive only) or even at any convenience store or gas station that has a payment machine. (This idea is not new. A decade ago I drove a toll road in Melbourne which lets you buy a toll pass at a gas station after you drive the road.)

Or, of course, just pay the fines if they are not that much more expensive, on average than buying tokens.

Even carpoolers could register that they carpooled, in case a problem comes up. Users will want to register an e-mail address or app address with the system under their plate to get notices of fines. If you don't, notices would come by postal mail. If somebody else registers your plate and you don't, it might delay notice of fines but you would fix this after the first one. If the typical toll is $3, and the fine is $300, you probably would get a fine notice you need to nullify perhaps every 75 uses on average. This makes paying cheaper. The smartphone app would also notice when you travel the route and remind you.

To protect privacy, the system would not remember tokens it issues, and it would erase all images once it was confirmed the car was legit (carpool, allowed vehicle or had a token.) Only the images of non-carpools who did not respond with their token would be retained for issuing fines to their car.

There can be problems with photo enforcement if it is dark (as it is during winter for portions of rush hour) or in places where the sun is at just the wrong angle. The latter can be fixed because we know just where the sun will be. The former is more challenging. Cameras would need to be placed in line with suitable street lights, and have larger lenses. During the day used cell phones in rainproof cases with tiny solar panels could do the job at low cost.