Thanks to you both for the positive encouragement.... :-) I guess I am somewhat inured to traffic, having been a motorcycle commuter for years. I still have to remind myself that the bicycle doesn't have the motorcycle's acceleration to get out of problem situations.

The cycling part of the commute is 20 miles round-trip. Fortunately that is split up into six segments so it seems less strenuous (except the last leg, going up those hills - argh). I am not sure how long the entire commute is including the trains but I imagine it's close to 100 miles. The trains are very fast, though. When I take the motorcycle, it's a more direct route so it's about 75 miles each way.

Some folding bikes don't ride well but the Brompton is actually pretty good. It's not a super-fast ride but IMHO it's a good compromise between outstanding foldability and a zippy ride with a mini rear suspension, and even good cargo capacity. There are faster-riding folders or separables (e.g., Moulton, Airnimal, Bike Friday, some Dahons) but they don't fold nearly so quickly or into as small a package. You could definitely take a road bike on the LA Metro but for me that becomes an obstacle on crowded trains. I like to be able to fold the bike and sit down rather than standing to hold up the bike. Also, my folder has a lightweight cover so I can cover it up when it's folded. Usually that's not necessary but there are times when creepy guys start paying a little too much attention to the bike, and I like the option of turning it into a generic-looking package - people don't even know it's a bike when the cover is on. Also, on our local buses, the bus racks only accept two bikes at a time, so if the rack is full, you have to wait for the next bus. All the local buses and trains have to take folding bikes all the time. Lots of people, though, take their road bikes and that seems to work very well for them so I don't want to discourage that in any way. I guess it's just a matter of different strokes for different folks.