Mayor Vincent Gray invited everyone aboard his time machine on Tuesday to check out a “Vision for a Sustainable D.C.” By the year 2032, if all goes according to this plan, we’ll have cut our obesity rate, energy consumption and greenhouse gas emissions all by 50 percent, attracted 250,000 new residents and made every D.C. waterway fishable and swimmable.

Of course, the part of the strategy to turn Washington into the “healthiest, greenest and most livable city” in the country that caught my attention was the transportation goal: 75 percent of all trips made by walking, biking or transit. That doesn’t seem so out there to me — most of my friends already hit that number, and if people don’t, it’s an awesome aspiration.

But several commenters at think the idea is just nuts. “And how do tourists — especially retired couples, disabled people and families who drive their cars to get to the nation’s capital — fit into this vision of D.C. without cars?” asked Kathy8. “Which tourists are going to bike to a restaurant?” wondered 8-Man2. And that charmer junkie4politics opined: “This city just doesn’t get it that no matter what they say or do, cars and trucks are, and always will be, as big a part of the fabric of this nation as baseball and apple pie.”

I’d argue that it’s these folks who don’t get it. Reducing the number of car trips doesn’t mean eradicating the automobile (just as cutting obesity doesn’t mean saying goodbye to delicious apple pie). Tourists are already biking not only to restaurants but to all of D.C.’s destinations thanks to the rapidly expanding Capital Bikeshare program, which finally managed to install some stations on the Mall. Seriously, my — pregnant! — friend visiting last week got around exclusively with CaBi.

And Kathy, honey, you’re exhibiting a fundamental lack of understanding of public transportation. Many seniors and disabled people can’t drive cars, so they need trains, buses and Washington’s future streetcar network more than any of us.

Granted, the current system has some accessibility issues (along with quite a few other issues, as the derailment this week reminded us). A recent study by ergonomics consultants Alison G. Vredenburgh and Ilene B. Zackowitz — and highlighted by the local blog, which is devoted to disabled Metro rider advocacy — noted the potential headaches caused by broken elevators, no place to secure wheelchairs on trains and the wide gaps between the platforms and trains.

The fixes to these problems aren’t going to arrive in a car. But hopefully, they’ll come via time machine. Over the next 20 years, the city and WMATA and all of us will have to make changes to bring this sustainable vision to life.