San Diego (transit.511sd.com)
San Francisco (sfmta.com, bart.gov, caltrain.com)
Light rail, bus: Base fare $2, $0.75 senior. Cable car $6. Unlimited passes, including cable car, one-day $14, three-day $22, seven-day $28; good deals if you want to ride cable cars.
Regional rail: Fares based on distance. Bart, seniors 62.5 percent off, CalTrain, seniors pay half price, day pass double one-way fare.
Light rail, bus: Base fare $2 to $2.80, depending on distance; $0.75 for seniors requires ID issued in advance or online. Day passes cost twice one-way fares good for moving around town.
Subway: Regular fares based on distance and peak/off-peak times, pay $1 per ride extra without pre-issued SmarTrip card. Bus base fare $1.60 with SmarTrip $1.80 without. Senior discounts roughly 50 percent off require Senior SmarTrip card issued in advance at a few stations or online.
Also worth noting: Although not on the TripAdvisor list, in Philadelphia, seniors travel free on subway, light rail, and bus and for $1 per ride on regional rail within Pennsylvania. For other cities, Google "city public transit" for details.
(Send e-mail to Ed Perkins at eperkins(at)mind.net. Perkins' new book for small business and independent professionals, "Business Travel When It's Your Money," is now available through http://www.mybusinesstravel.com or http://www.amazon.com)