> It's not as hard as you make it out to be. I live in Japan where these (very effective) safety doors have been rolling out for more than a decade.

Japan has one of the largest passenger rail industries with massive capital investment. They are quite good at station design and engineering and I definitely applaud their use of enclosed platforms - which ironically came about more out of a desire to reduce wasted energy on air-conditioned subway stations ventilating into the tunnels.

> I don't think there is any need for computerized stop-assist. On at least some of the trains here, and I think most, it is up to the driver top stop the train. Once in a great while, they accidentally overshoot by a foot or two, apologize on the loudspeaker, and back the train up to align it properly.

Lighter trains can do so manually, but on the majority of lines in the JR network commuter trains and shinkansen have a computerized stop-assist that will get the train within a few inches of the desired point. Some lines do not use the computerized stop-assist (Yamanote, Chuo, etc.) as they are primarily above ground with longer platforms.

> There is not need for a homogeneous vehicle fleet, either. In fact, in Japan just about every line gets a unique train design (which does seem weirdly inefficient, but whatever). At first they we in fact designing different safety doors to match every train. But later, to cut costs and make it possible to have safety gates at stations featuring trains with different door configurations stop, they just designed wider safety gate that can open more on one side than the other.

In Japan, the majority of trains use very similar door configurations. They either have end-cap doors, or 2-4 doors with even distribution. Most commuter lines with the enclosed platforms employ a single type of rolling stock on a dedicated platform.

The Keisei railway and other private roads have platform gates, which are a bit different. Those are waist height and are simply to keep people from stepping to the edge when express trains pass. I think you are referring to these, and they are definitely useful, but see my final point as to why they aren't feasible for Caltrain.

> This brings to mind another simple optimization -- if your trains really suck so much ass that the driver is unable to stop them with reasonable precision, just make the safety gates six feet (or ten feet, whatever) wider than the train doors. (Easier if you make them lift up to open rather than opening laterally.) There is no need for the safety doors to be the same width as the train doors.

They don't suck ass, they are just quite heavy. A Caltrain rolling stock set is 160 tons for the locomotive and then 20 tons per car (est.) That is far, far heavier than any JR trainset in operation and much harder to stop. You don't get electro-pneumatic brakes to stop every car at exactly the same rate - instead you have dynamic brakes and air. Try to stop that with some precision :P

In the end, the main sticking point isn't the rolling stock anyway. The problem is that the platforms are open and anyone can walk on at anytime. There is no way in current Caltrain stations to restrict access with any degree of certainty. To change this would require grade separation and massive overhauls of each station at the very least.

Japanese trains exclusively use raised platforms and 99%+ of stations have restricted access (with only rural/flag stops being the exception). This makes it easy to use some sort of safety mechanism to restrict access to the tracks. Trains in the US are far different and don't really fit the same mold, unless you get to the Northeast and ride the NYC commuter trains (MTA, LIRR, ConnDot, etc.)

I have always felt enclosed platforms are necessary to move passenger rail forward in the US, but they are a long ways off - and likely will never happen regardless.