It’s been against the law in Maryland for more than four years now, but with winter biding its time before it grabs Southern Maryland in its icy grip, it’s worth reminding ourselves of it again: You’re not supposed to leave your vehicle idling when you’re not in it.

Passed by the General Assembly in 2015, and going into effect Oct. 1 of that year, the law does take into account some features of newer cars. If your vehicle has a remote ignition system, it’s OK by state law to let it warm up for up to five minutes.

Leaving the car running is also OK if it’s on private property and locked. Of course, that’s when that second set of keys or remote opener fob comes in handy — but don’t forget that car thieves have been working hard to hack into keyless systems.

In any circumstance, though, you are not supposed to let your vehicle idle for more than five minutes in Maryland. That’s for our safety, as well as for the environment.

But on a cold morning, who hasn’t started up the car to let it warm up and defrost while going back inside for a cup of coffee or to finish getting ready? An unlocked, running car seems like an inviting target for a thief, but that couldn’t happen in your own driveway, right? Think again.

AAA Mid-Atlantic warns against becoming easy prey for a “puffer,” a would-be auto thief who sees the plumes of condensation billowing from the tailpipe of an idling car.

And as it turns out, car makers and other automotive experts are now saying that letting a modern vehicle warm up at all is a waste of time and gas these days.

Your Uncle Fred might have needed to let his 1973 Plymouth Duster idle for 10 minutes on a frigid day before heading to work, but Popular Mechanics magazine states emphatically that today’s vehicles don’t need to be coaxed into action on an icy morning. The magazine says warming up the car before driving it is a relic of the past, “dating back to the time when carbureted engines dominated the road. Idling does surprisingly little to warm the actual engine” in vehicles that have rolled off the assembly line in the past 30 years or so. “It takes five to 15 minutes for your engine to warm up while driving, so take it nice and easy for the first part of your drive.”

Anybody who tells you otherwise, according to Popular Mechanics, is just trying to sell you more gasoline. Our 21st-century automobiles with their computerized fuel injection systems simply do not need to be warmed up, but just driven gently when you’re first out of the driveway.

At the same time, briefly warming and defrosting a car does make it easier to knock off any overnight ice that may have accumulated on the windshield and windows. And if your vehicle is equipped with heated mirrors, so much the better.

“If you average idling your vehicle 10 minutes a day during the three winter months, you are simply increasing the wear and tear on your vehicle by 11 additional hours,” said James Spires, regional manager for AAA Mid-Atlantic’s car care centers. “You are also wasting an average of about 5½ gallons of gasoline. If you must, the best way to warm a modern engine is to start it and allow it to idle for 15 to 30 seconds while you fasten your seat belt and check the mirrors. A little longer idle time may be appropriate in the winter if you need to clear snow and ice from the windshield and other parts of the car.”

Over the past couple of decades, Southern Maryland has tended to get some of its nastiest winter weather in February.

So when you need to get moving to start your day during those certain-to-be-coming cold snaps, use common sense and less gasoline while warming up your vehicle.

Then proceed safely. It’ll be spring before you know it.