This is a commuter rail line: San Jose’s Altamont Commuter Express (ACE). It connects nine stations, one of them sort of close to a medium-sized employment center, one with a light rail connection to a suburban employment center, and seven which are basically no more than parking lots. There are six trains a day: three towards San Jose in the morning, three away from San Jose in the afternoon. The last train leaves at 5:35 p.m., and there’s no weekend service.

This is also a commuter rail line: Tokyo’s Yamanote Line. It connects 29 stations. All of them are in walkable places, including several major employment centers; all but 2 have connections to other rail transit lines. Trains run every 2.5 minutes at rush hour, and nearly as frequently the rest of the day, from 4:30 am to 1:20 am, seven days a week.

Yes, these are both commuter rail lines. But “commuter rail” is a technology, and what matters in transit is not technology but level of service. There is no doubt that a train every 2.5 minutes is different than a train every half hour (or no train at all), that a station that’s within a 5 minute walk from thousands of jobs is different that a station in an open field, that a connection to a reliable transit service that runs every 5 minutes is different than a connection to an occasional shuttle bus that gets stuck in traffic.

These two lines are the same basic technology, but entirely different sorts of operations. And the numbers back that up: ACE carries 3,700 trips a day, while the Yamanote Line carries 3,500,000. It’s not technology that really matters, it’s service. And there’s a whole range of service: these are two ends of a spectrum with many other possibilities in between.

“We need commuter rail” is an incomplete statement. So is “we need commuter rail to Galveston.” “We need rail transit from Houston to Galveston that runs every 20 minutes all day every day, makes the trip in about an hour, and connects conveniently to UTMB, NASA, Downtown Houston, UH, the Texas Medical Center, and Uptown Houston” is the kind of statement you can design a line around.