I question whether one second-hand tweet is a useful data point.

I have ridden BART most workdays for the past 7 years. I have encountered trains with stuck doors a several times, and on none of those occasions was the train put out of service. In fact, they even have pre-printed stickers that say something to the effect of "This door is not working; please use other door." I have seen these perhaps half a dozen times since I began riding BART regularly.

Note that these doors were stuck _closed_. It would be an obvious safety hazard if the door was stuck open - in that case I can well imagine that the operator would not move the train from the station.

Door stuck closed are also a safety hazard as they can hinder evacuation in case of fire or other emergency and make it more difficult for rescue teams to enter the train. Imagine a packed railroad car full of smoke, very bad visibility and panicking people inside. A stuck door can make the difference between life and death.

That actually seems reasonable to me. There's no easy way to swap a car out of the train in-station, and it would be next to impossible to keep everyone out of one of the cars in the train. Would probably be better if they had some way of quickly locking the door closed, but the trains don't seem to have that feature.

Meanwhile on Muni: http://www.youtube.com/watch?v=ZyQAy8PzgZ8

This has happened a few times this year. Although the video is dated April 1, I can vouch for the authenticity; this is my neighborhood line and I have gotten used to the recurring problems of particular rail carriages. If it were up to me I'd scrap the light rail on the west side of the city and put in buses instead.

It took me most of the way through that video to realize that one of the doors was open. It's frightening that the door malfunctioned and that the sensors apparently aren't working (or don't exist).

I've ridden Muni only a handful of times. On one of them, a homeless man threatened to cut my throat with a knife. Admittedly, it was because I stepped up when he began screaming at a non-white person (Middle-Eastern, perhaps, with some variant of head scarf) and her toddler.

Oh the sensors work - they make an earsplitting beeping when the door fails to close. But sometimes the drivers just take off anyway. This is a proble, with some of the older drivers who are only thinking of their pension in my view; there are a lot of hardworking and safety-minded drivers and station crew, but it only takes one irresponsible person to ruin the good work of many others.

I've been on trains where both doors in a car broke and the train kept going. The mechanic was fixing the door as the train went along, even.