I've written a few times about the "Selfish Merge" problem. Recently, reading the new book Traffic: Why We Drive the Way We Do by Tom Vanderbilt, I came upon some new research that has changed and refined my thinking.
The selfish merge problem occurs when two lanes reduce to one. Typically, most people try to be "good" and merge early, and that leaves the right lane, which is ending, mostly vacant. So some people zoom ahead of everybody in the right lane, and then merge at the very end. This is selfish in the sense that butting into any line is selfish. Even if overall traffic flow is not reduced (and even if it is increased) the person butting in moves everybody back one slot so they can get ahead by many slots. This angers people and generates more counter-productive behaviour, including road rage, and attempts to straddle the lanes so that the selfish mergers can't move up to the merge point.
In Traffic, Vanderbilt writes of surprising research that changed his mind, which showed that, in simulations, some merging forms provided up to 15% more traffic throughput than proper attempts at a zipper merge. In particular, a non-selfish merge fully using the vanishing lane worked better than the typical butt-in situation described at the top.
In this merge, which I'll call the "slow and fair merge," drivers are told to use both lanes up to the merge-point, and then to fairly "take their turn" at the merge point entering the continuing lane. Nobody is selfish here, in that nobody butts ahead of anybody else, but both lanes are fully utilized up to the merge point.
This problem is complex, I believe, because there is a switch-over point, which I call the "collapse" point. This is the point at which the merge flow becomes high enough that traffic collapses to "stop and go" mode, before and at the merge-point. Before that point, in lighter traffic, there is little doubt (for reasons you will see below) that the "cooperating fast zipper" merge results in the best traffic flow. In particular, there are traffic volumes where you could either have cooperating zipper or "slow and fair" but cooperating zipper would do a fair bit better. There are also traffic volumes where cooperating zipper just isn't possible any more, and we will either have "slow and fair" (which has the best volume) or "selfish merge" which has a worse volume.
Real world experiments show different results from the theoretical. In particular, many drivers, used to the anarchic selfish-merge approach, don't understand fair and slow, even when signs are explicit about it, and so they resist using both lanes and try to merge early. They also try to straddle, devolving to selfish merge. An experiment with digital signs which changed from advising drivers to zipper-merge in light traffic to advising "use both lanes" and "merge here, take your turn" in heavier traffic was disobeyed in fair and slow mode by too many drivers. The experiment ended before people could learn the system.
Ford is making a new car-limiting system called MyKey standard in future models. This allows the car owner to enable various limits and permissions on the keys they give to their teen-agers. Limits included in the current system include an 80 mph speed limit, a 40% volume limit on the stereo, never-ending seatbelt reminders, earlier low-fuel warnings, audio speed alerts and inability to disable various safety systems.
As part of my research into robotic cars, I've been studying the energy efficiency of transit. What I found shocked me, because it turns out that in the USA, our transit systems aren't green at all. Several of the modes, such as buses, as well as the light rail and subway systems of most towns, consume more energy per passenger-mile than cars do, when averaged out. The better cities and the better modes do beat the cars, but only by a little bit. And new generation efficient cars beat the transit almost every time, and electric scooters beat everything hands down.
Note to new readers: This article explores the consequences of using so much fuel to produce our food. If you come out of it thinking it's telling you to drive rather than get some exercise, you didn't read it! But if you like surprising numbers like this, check out the rest of my Going Green section and other sections.
Rental car companies are often owned by car manufacturers and are their biggest customers. As cars get more and more computerized, how about making rental cars that know how to personalize to the customer?
When Hertz assigns me a car, they could load into its computer things like the dimensions of my body, so that the seat and mirrors are already set for me (simply remembered from the last time I rented such a car, for example.) If I have a co-driver, a switch would set them for her. The handsfree unit would be paired in advance with my bluetooth phone.
I have written before about the selfish merge which is a tricky problem to solve. One lane vanishes, and the merge brings everybody to a standstill. Selfish drivers zoom up the vanishing lane to the very end and are let in by other drivers there, causing the backup. The selfish strategy is the fastest way through the blockage, yet causes the blockage.
In many cities, the transit systems have GPS data on the vehicles to allow exact prediction of when trains and buses will arrive at stops. This is quite handy if you live near a transit line, and people are working on better mobile interfaces for them, but it's still a lot harder to use them at a remote location.
Many cities (and airports) have official taxi monopolies. They limit the number of cabs in the city, and regulate them, typically by issuing "medallions" to cabs or drivers or licences to companies. The most famous systems are in London and New York, but they are in many other places. In New York, the medallions were created earlier in the century, and have stayed fixed in number for decades after declining from their post-creation peak. The medallion is a goldmine for its "owner." Because NY medallions can be bought and sold, recently they have changed hands at auction for around $300,000. That 300K medallion allows a cab to be painted yellow, and to pick up people hailing cabs in the street. It's illegal for ordinary cars to do this. Medallion owners lease the combination of cab and medallion for $60 to $80 for a 7-9 hour shift, I believe.
Here in San Francisco, the medallions are not transferable, and in theory are only issued (after a wait of a decade or more) to working cab drivers, who must put in about 160 4-hour shifts per year. After that, they can and do rent out their medallion to other drivers, for a more modest rental income of about $2,000 per month.
On the surface, this seems ridiculous. Why do we even need a government monopoly on taxis, and why should this monopoly just be a state-granted goldmine for those who get their hands on it? This is a complex issue, and if you search for essays on taxi medallions and monopoly systems you will find various arguments pro and con. What I want to get into here is whether some of those arguments might be ripe for change, in our new high-tech world of computer networks, GPSs and cell phones.
In most cities, there are more competitive markets for "car services" which you call for an appointment. They are not allowed to pick up hailing passengers, though a study in Manhattan found that they do -- 2 of every 5 cars responding to a hail were licenced car services doing so unlawfully.
In the SF Bay Area, there are carpool lanes. Drivers of fuel efficient vehicles, which mostly means the Prius and the Honda Civic/Insight Hybrids can apply for a special permit allowing them to drive solo in the carpool lanes. This requires both a slightly ugly yellow sticker on the bumper, and a special transponder for bridges, because the cars are allowed to use the carpool lane on the bridge but don't get the toll exemption that real carpools get.
In one of my first blog posts, I wrote about virtual right-of-way, a plan to create dedicated right of way for surface rail and bus transit, but to allow cars to use the RoW as long as they stay behind, and never in front of the transit vehicle.
I proposed one simple solution, that if the driver has to step on the brakes because of a car in the way, a camera photographs the car and plate, and the driver gets a fat ticket in the mail. People would learn you dare not get into the right-of-way if you can see a bus/train in your rearview mirror.
Parking at airports seems a terrible waste -- expensive parking and your car sits doing nothing. I first started thinking about the various Car Share companies (City CarShare, ZipCar, FlexCar -- effectively membership based hourly car rentals which include gas/insurance and need no human staff) and why one can't use them from the airport. Of course, airports are full of rental car companies, which is a competitive problem, and parking space there is at a premium.
Right now the CarShare services tend to require round-trip rentals, but for airports the right idea would be one-way rentals -- one member drives the car to the airport, and ideally very shortly another member drives the car out of the airport. In an ideal situation, coordinated by cell phone, the 2nd member is waiting at the curb, and you would just hand off the car once it confirms their membership for you. (Members use a code or carry a key fob.) Since you would know in advance before you entered the airport whether somebody is ready, you would know whether to go to short term parking or the curb -- or a planned long-term parking lot with a bit more advance notice so you allocate the extra time for that.
Of course the 2nd member might not want to go to the location you got the car from, which creates the one-way rental problem that carshares seem to need to avoid. Perhaps better balancing algorithms could work, or at worst case, the car might have to wait until somebody from your local depot wants to go there. That's wasteful, though. However, I think this could be made to work as long as the member base is big enough that some member is going in and out of the airport.
I started thinking about something grander though, namely being willing to rent your own private car out to bonded members of a true car sharing service. This is tougher to do but easier to make efficient. The hard part is bonding reliability on the part of all concerned.
Read on for more thinking on it...
It does get hard to be a privacy advocate when it's easy to think of interesting apps that make use of tracking infrastructure. Here's one.
How often have you wanted to talk to somebody in a car next to you on the road? Consider a system where people could register their licence plate(s) with their cell phone account. Then, if they had done this, you could call a special number on your own cell phone, and enter the numeric part of their licence plate.
Every driver of a regular car knows this frustration well. You're behind a big SUV or Minivan and you can no longer see what's happening ahead of you, the way you can with ordinary cars. This is not simply because the ordinary cars are shorter, it's because you can see through the windows of the ordinary car -- they are at your level.
More cars are being made "drive-by-wire" where the controls are electronic, and even in cars with mechanical steering, throttle and brake linkages, there also exist motorized controls for power steering and cruise control. (It's less common on the brakes.)
As this becomes more common, it would be nice if one could pop in a simple, short duration control console on the passenger's side. It need not be large, full set of controls, it might be more of the video game console size.
Transit is of course more efficient than private cars, many people on one vechicle. But because a round-trip for a couple or family involves buying 4 to 8 single tickets, couples and families who have cars will often take their cars unless parking is going to be a problem. For example, for us to go downtown it's $6 within SF. For people taking BART from Berkeley or Oakland it's $13.40 for 2 people. Makes it very tempting to take a car, even if it costs a similar amount (at 35 cents/mile, 15 of those for gasoline in a city) for the convenience and, outside of rush-hour, speed.
Through the SV100 I was given an interesting product called the [Trafficgauge](http://www.trafficgauge.com/" rel="nofollow) to review. It's a small thick-PDA sized live map of the highways of your area, with indicators as to where there are traffic slowdowns. They cover about a half dozen cities.
I've been writing a bunch about transportation of late, and I got the chance to have lunch with Robin Chase, founder of Zipcar, and talk about the economics.
She proposes that we really need to make the true cost of our transportation visible to solve many of our problems (congestion, pollution, etc.) It's often been described just how much of a subsidy the U.S. and in particular California gives to the car driver, but to most people it's not too visible.
She's particularly interested in changing the rules on parking. We subsidize parking a lot. Most people are aware of the use of roadsides for free or cheap parking on public land. Robin proposes getting rid of the requirements that force building developers to provide adequate parking for their building. Most people think these are a good idea, because otherwise developers would not provide parking, and the cars coming to the building would suck up all available parking in the area and there would quickly not be any.