By the time this story runs, I’ll be reclined for the next four hours on a late-morning train to New York. From Boston, there is no better way to get there than Amtrak. No unwashed floors from the thousands of people waddling past airport security in their dirty socks, belts in hand, like a huge middle-school locker room. No crowded, stale Peter Pan buses that stop at that same Roy Rogers halfway through the trip. And no traffic, not at any time in the day.

Amtrak, despite its high-speed dreams that will never be realized, is the most relaxing form of travel. You pay your fare, show up and walk aboard without hassle. The trip is quiet, smooth, clean and, even when fully booked, offers enough room to stretch out. The price is usually silly, to the point where it’d be more economical to drive a Bugatti Veyron for those 220 miles and park it in a New York garage. Seriously, we’re talking tickets costing more than $100, without any Acela frills, one-way.

But aside from price, many Amtrak cars have a pretty neat feature most road cars don’t: an automatic start/stop system that can shut the diesel engine down at idle. I’ll leave the specifics of electric traction motors to the train enthusiasts, but the point is simple: Turn off the belching engine when it’s not being used to pull.

More than 30 states have anti-idling laws in effect, mostly aimed at diesel-powered commercial trucks and school buses. Yet outside of specific, controlled areas -- say, the cab stands at Boston Logan Airport, which have signs posted and lots of state troopers watching -- it’s a pretty difficult rule to enforce, especially when it’s cold out.

When I run along the Charles River during rush hour, I restrict my breathing while passing the hundreds of drivers trapped in traffic. Huffing fumes, even for a matter of seconds, is enough to make me nauseated, not to mention whatever it’s doing to my lung tissue. In Mexico City, you are practically licking the tailpipe of every 1960s Beetle and overloaded bus in the capital. The air quality is so horrendous and the traffic so absurd (when turning, drivers crowd intersections three rows deep to get across) that you never, ever get a fresh gulp of air. Other major cities in India and China, from what I keep reading, are even worse. No one can move, no one can breathe.

So it’s with great pleasure that I see auto start/stop systems making their way to U.S. cars such as the 2013 Ford Fusion, even though it’s a $295 option. Today, automakers realize that slapping the word “hybrid” comes with clear expectations -- namely, superior fuel economy, higher prices and draining performance. When General Motors rolled out the Chevrolet Malibu and Saturn Aura hybrids in 2007, the cars sold at a $4,000 premium, the norm for most hybrids at the time, but delivered comparatively meager fuel savings. There was no mind-blowing surge in fuel economy as on the 2010 Ford Fusion Hybrid, just a few ticks in the city rating. They failed.

Or did they? Although sales flopped, the technology was simple and cheaper than the complexity of a full-fledged hybrid. A larger starter motor and a tiny battery pack made for a decent auto start/stop system -- if not an actual hybrid that could travel on electric power. There were no major powertrain modifications.

Now, GM has beefed up the system with a larger battery on the 2012 Buick LaCrosse and upcoming 2013 Chevrolet Malibu and called it eAssist. But even without a battery, is there any marketing shame to selling a cleaner car in the city? Are people really going to think their engines are dying when another part of their brains know that they’re actually saving precious gas money? I think not. These nonbattery systems, for minimal cost, are worth it to the mom jogging along the river with her baby.

Of course, when automakers fit bad auto start/stop systems, it’s easy to think something’s broken. The Honda Insight shudders the steering column, hard, when shutting down and restarting, at least it did when I drove one two years ago. So did the now-discontinued Nissan Altima Hybrid. A Porsche Cayenne Turbo, after I found the start/stop button among 44 other buttons on the console, was plain goofy trying to restart its giant 4.8-liter V8 engine, revving it high as if the engine were cold. It felt as if the Cayenne were burning more fuel.

Two of the best auto start/stop systems happen to be on the two best hybrids, the Toyota Prius and Ford Fusion Hybrid. Their smoothness and very mild vibrations when pulling away from a stop on gasoline are noticeable only to journalists looking for flaws, and to hypermilers. The Volvo V60 I tested in Sweden over the winter -- a manual transmission, mind you -- was just as brilliant and rattle-free. In traffic, these systems are a real blessing, and you never lose air conditioning or any other electrical functions.

Porsche and Mercedes-Benz, by making the driver switch on this fuel-saving feature every time, have it wrong. BMW, in its new 3 Series, switches the system on by default, as does Ford. Automatic start/stop systems should work exactly as they sound: seamless, and without disruption. Otherwise, what’s the point?