Two young parents with three children got on the Green Line at Western Avenue in St. Paul the other day, heading west. It was midday — nowhere near either of the two rush hours. The mother juggled an awkward wheeled suitcase, and several other members of the party were carrying toys and other items. "Wonderful," I thought from my seat half a car length away: part of what the Green Line is designed for — a sleek connectivity among diverse populations and neighborhoods, linking all of them to the center of the Upper Midwest's biggest business city, the State Capitol and its downtown, and the large Big Ten university campus between them.

My uncomplicated smugness over our new, 21st-century urban amenity turned to horror at what happened when we reached the Lexington Parkway station. I watched the family gather up its things and head for the door. But just after the first young child had exited onto the platform, one or two people pushed by, entering the car, and the doors closed. The father, still inside, groped around on the door, banging on it trying to open it as the train left the station, stranding his 5- or 6-year-old on the platform.

The mother raced to the front end of the car as if in search of a driver, but we were in the third and last car. Frantically looking about, she found a small emergency call box near the opposite door, pressed a button, and shouted something into it as the train rolled forward, now a block or more from the Lexington Station. "I can't understand what you are saying," a voice said back.

"Where are you?" the mother screamed into the little box, apparently not sure if the voice of authority was even on the train. There was no response.

By then the train was halfway to its next stop, Hamline. I could not figure out how to help, fearing that any interrupting distraction might further impede this panic-stricken family. Better to let them focus on reuniting, however they might work that out, I decided.

Maybe the kid was crying on the Lexington platform and some adult was there to somehow understand and help . The family huddled at the door and bolted from the train at Hamline, the two youngest children out ahead of the parents. After the doors closed, I heard the father shouting, either calling impossibly far down the line to Lexington or just venting; I could not make out his words.

I love the Green Line. I'm eager for the A Line bus rapid transit to become a reality, since we live just a block from one of its proposed Snelling Avenue stations. How perfect to get so readily to either of the light-rail lines. But I'm haunted by what happened on a nearly empty train, that stranding of a child on a probably empty platform. If his or her parents were so unsure how the system works, what must that little child have thought? What did she or he do? How did the parents reunite?

I doubt that some kind of emergency cord or brake is practical. It's not hard to imagine the abuses or accidents that would occur. I'm tired of the "if we can put a man on the moon, then why can't we … ?" cliché for every technical problem. Some problems are not just technological.

But surely Metro Transit can devise some combination of technological connectivity, driver training and public education to make such events, if not impossible, at least far less likely.

Less than two months into its operation, this line serves a somewhat different population than does the Blue Line, which connects the Mall of America and suburbia with the airport and downtown Minneapolis, passing only briefly through denser neighborhoods. While officials tweak the system to enable much-desired faster travel between the Green Line's two endpoint downtowns, they must also consider riders such as that family only going a few stops.

We cannot leave such customers in the dust, or their children abandoned on what is for them a dangerous platform.

James McKenzie, of St. Paul, is a retired academic and a writer.