I would think that the shareroller is a good solution, at least for shorter trips.

My guess is that BART is train or buss? I do not often use them with the bike, and I tend to take the Brompton when I do. We are lucky that we can roll the unfolded bike (I always detatch pedals) all the way up to the buss/trains.

My reason for looking at a assisted trailer is that I own a 20" e-bike and it is heavy... plus I am sometimes thinking I want e-assist on one of the other bikes- but not enough to buy and install becouse I may not want it there all the time. Therefor I have recently been thinking of an e-assist trailer instead. Not sure what I`ll end up doing.

The bike i have installed the e-kit on is not really good for rolling folded, and I only want to lift it in and out of the car.

I am looking forwards to bikes that easely charge when riding plus solar cells also effective enough to charge while riding so we do not need the heavy batterys. Maybe solar cell clothing?