My wife is 8 months pregnant, and even then, even when she asks nicely, here in SF people will not give up their seats to let her sit down. They won't for elderly, even folks on crutches. I've seen it happen so many times. Keep in mind it is federal law to do so. Too bad you can't use that as an excuse to avoid an assault charge when some 30 something able bodied commuter refuses to give up his seat for some 90 year old lady.