Caltrain is the commuter rail line of the San Francisco peninsula. It's not particularly good, and California is the land of the car commuter, but a plan was underway to convert it from diesel to electric. This made news this week as the California Republican house members announced they want to put a stop to both this project, and the much larger California High Speed Rail that hopes to open in 2030. For various reasons they may be right about the high speed rail but stop the electric trains? Electric trains are much better than diesel; they are cleaner and faster and quieter. But one number stands out in the plan.

To electrify the 51 miles of track, and do some other related improvements is forecast to cost over 1.5 billion dollars. Around $30M per mile.

So I started to ask, what other technology could we buy with $1.5 billion plus a private right-of-way through the most populated areas of silicon valley and the peninsula? Caltrain carries about 60,000 passengers/weekday (30,000 each way.) That's about $50,000 per rider. In particular, what about a robotic transit line, using self-driving cars, vans and buses?

Paving over the tracks is relatively inexpensive. In fact, if we didn't have buses, you could get by with fairly meager pavement since no heavy vehicles would travel the line. You could leave the rails intact in the pavement, though that makes the paving job harder. You want pavement because you want stations to become "offline" -- vehicles depart the main route when they stop so that express vehicles can pass them by. That's possible with rail, but in spite of the virtues of rail, there are other reasons to go to tires.

Fortunately, due to the addition of express trains many years ago, some stations already are 4 tracks wide, making it easy to convert stations to an express route with space by the side for vehicles to stop and let passengers on/off. Many other stations have parking lots or other land next to them allowing reasonably easy conversion. A few stations would present some issues.

Making robocars for a dedicated track is easy; we could have built that decades ago. In fact, with their much shorter stopping distance they could be safer than trains on rails. Perhaps we had to wait to today to convince people that one could get the same safety off of rails. Another thing that only arrived recently was the presence of smartphones in the hands of almost all the passengers, and low cost computing to make kiosks for the rest. That's because the key to a robotic transit line would be coordination on the desires of passengers. A robotic transit line would know just who was going from station A to station J, and attempt to allocate a vehicle just for them. This vehicle would stop only at those two stations, providing a nonstop trip for most passengers. The lack of stops is also more energy efficient, but the real win is that it's more pleasant and faster. With private ROW, it can easily beat a private car on the highways, especially at rush hour.

Another big energy win is sizing the vehicles to the load. If there are only 8 passengers going from B to K, then a van is the right choice, not a bus. This is particularly true off-peak, where vast amounts of energy are wasted moving big trains with just a few people. Caltrain's last train to San Francisco never has more than 100 people on it. Smaller vehicles also allow for more frequent service in an efficient manner, and late night service as well -- except freight uses these particular rails at night. (Most commuter trains shut down well before midnight.) Knowing you can get back is a big factor in whether you take a transit line at night.

An over-done service with a 40 passenger bus every 2 seconds would move 72,000 people (but really 30,000) in one hour in one direction to Caltrain's 30,000 in a day. So of course we would not build that, and there would only be a few buses, mainly for rush hour. Even a fleet of just 4,000 9 passenger minvans (3 rows of 3) could move around 16,000 per hour (but really 8,000) in each direction. Even if each van was $50,000 each, we've spent only $200M of our $1.5B, though they might wear out too fast at that price, so we could bump the price and give them a much longer lifetime.

Energy

These vans and cars could be electric. This could be done entirely with batteries and a very impressive battery swap system, or you could have short sections of track which are electrified -- with overhead rails or even third rails. The electric lines would be used to recharge batteries and supercapacitors, and would only be present on parts of the track. Unlike old 3rd rail technology, which requires full grade separation, there are new techniques to build safe 3rd rails that only provide current in a track segment after getting a positive digital signal from the vehicle. This is much cheaper than overhead wires. Inductive charging is also possible but makes pavement construction and maintenance much more expensive.

Other alternatives would be things like natural gas (which is cheap and much cleaner than liquid fuels, though still emits CO2) because it can be refilled quickly. Or hydrogen fuel cell vehicles could work here -- hydrogen can be refilled quickly and can be zero emissions. Regular fossil fuel is also an option for peak times. For example the rush hour buses might make more sense running on CNG or even gasoline. The lack of starts and stops can make this pretty efficient.

Stations, anywhere

In such a system, you can also add new "stations" anywhere the ROW is wide enough for a side-lane and a small platform. You don't need the 100m long platform able to hold a big train, just some pavement big enough to load a van. You can add a new station for extremely low cost. Of course, with more stations, it's harder to group people for nonstop trips, and more people would need to take two-hop trips -- a small van or car that takes them from a mini-station to a major station, where they join a larger group heading to their true destination.

Of course, if you were designing this from scratch, you would make the ROW with a shoulder everywhere that allowed vehicles to pull off the main track at any point to pick up a passenger and there would barely be "stations" -- they would be closer to bus stops.

Getting off the track

Caltrain's station in San Francisco is quite far from most of the destinations people want to go to. It's one of the big reasons people don't ride it. Vans on tires, however, have the option of keeping going once they get to the station. Employers could sponsor vehicles that arrive at the station and keep driving to their office tower. Vans could also continue to BART or more directly to underground Muni, long before the planned subway is ready. Likewise on the peninsula, vans and buses would travel from stations to corporate HQ. Google, Yahoo, Apple and many other companies already run transit fleets to bring employees in -- you can bet that given the option they would gladly have those vans drive the old rail line at express speeds. On day one, they could have a driver who only drives the section back and forth between the station and the corporate office. In the not too distant future, the van or bus would of course drive itself. It's not even out of the question that one of the passengers in a van, after having taken a special driving test, could drive that last mile, though you may need to assure somebody drives it back.

At-grade crossings

I noted above that capacity would be slightly less than half of full. That's because Caltrain has 40 at-grade crossings on the peninsula. The robotic vehicles would coordinate their trips to travel in bunches, leaving gaps where the cross-street's light can be turned green. If any car was detected trying to run the red, the signal could be uploaded to allow all the robotic vans to slow or even brake hard. Unlike trains, they could brake in reasonable amounts of time if somebody stalls on the old track. You would also detect people attempting to drive on the path or walk on it. Today's cameras and cheap LIDARs can make that affordable. The biggest problem is the gaps must appear in both directions (more on that in the comments.)

Over time, there is also the option in some places to build special crossings. Because the vans and cars would all be not very high, much less expensive underpasses could be created under some of the roads for use only by the smaller vehicles. Larger vehicles would still need to bunch themselves together to leave gaps for the cross-traffic. One could also create overpasses rated only for lightweight vehicles at much lower cost, though those would still need to be high enough for trucks to go underneath. In addition, while cars can handle much, much steeper grades than trains, it could get disconcerting to handle too much up and down at 100mph. And yes, in time, they would go 100mph or even faster. And in time, some would even draft one another to both increase capacity and save energy -- creating virtual trains where there used to be physical ones.

And then, obsolete

This robotic transit line would be much better than the train. But it would also be obsolete in just a couple of decades! As the rest of the world moves to more robocars, the transit line would switch to being just another path for the robocars. It would be superior, because it would allow only robocars and never have traffic congestion. You would have to pay extra to use it at rush hour, but many vehicles would, and large vehicles would get preference. The stations would largely vanish as all vehicles are able to go door to door. Most of the infrastructure would get re-used after the transit line shuts down.

It might seem crazy to build such a system if it will be obsolete in a short time, but it's even crazier to spend billions on shoring up 19th century train.

What about the first law?

I've often said the first law of robocars is you don't change the infrastructure. In particular, I am in general against ideas like this which create special roads just for robocars, because it's essential that we not imagine robocars are only good on special roads. It's only when huge amounts of money are already earmarked for infrastructure that this makes sense. Now we are well on the way to making general robocars good for ordinary streets. As such, special cars only for the former rail line run less risk of making people believe that robocars are only safe on dedicated paths. In fact, the funded development would almost surely lead to vehicles that work off the path as well, and allow high volume manufacturing of robotic transit vehicles for the future.

Could this actually happen?

I do fear that our urban and transit planners are unlikely to be so forward looking as to abandon a decades old plan for a centuries old technology overnight. But the advantages are huge:

• It should be cheaper
• Many companies could do it, and many would want to, to fund development of other technology
• It would almost surely be technology from the Bay Area, not foreign technology, though vehicle manufacturing would come from outside
• They could also get money for the existing rolling stock and steel in the rails to fund this
• The service level would be vastly better. Wait times of mere minutes. Non-stop service. Higher speeds.
• The energy use would be far lower and greener, especially if electric, CNG or hydrogen vehicles are used

The main downside is risk. This doesn't exist yet. If you pave the road to retain the rails embedded in them, you would not need to shut down the rail line at first. In fact, you could keep it running as long as there were places that the vans could drive around trains that are slowing or stopping in the stations. Otherwise you do need to switch one day.