It's strange to think that an electric commuter rail line rivaling BART in efficiency, speed, and comfort ran over 100 years ago between San Francisco and San Mateo, but run it did. The 40 Line, or San Mateo Interurban, began in 1892 with an initial segment operating between Market and Steuart Streets out to the county limits on San Jose Avenue. Three years later, the line reached Baden in present-day South San Francisco, and by 1903 service was opened all the way to downtown San Mateo. During the line's heyday, there was talk of extending it down the peninsula from San Mateo to Palo Alto to...