The plan looks pretty nice, and includes some beautiful features. Foremost among them is a new European-style train room that would be unprecedented in North America. Instead of boarding trains from a dim cavern below the parking garage, riders would board from a brightly-lit glass enclosure.

Despite that, I can’t help but feel a little bit nervous about the whole thing.

A hundred years ago, almost every major American city had a beautiful train station. Unfortunately many were destroyed during the 20th century. Of those that survived, the vast majority are mere shells of their former selves. Washington Union Station is one of the only exceptions. It’s an absolutely beautiful historic building that remains active, vital, and functioning as an extremely busy train station. In my opinion, it’s the best intercity rail station in America.

And so when plans come forward to dramatically change it, I get a little bit worried. So many of the country’s train stations have been ruined by redevelopment, it’s clearly a dangerous business.

But Union Station does legitimately need to be expanded. It’s a bottleneck that limits all of its rail users: Amtrak, MARC, VRE, even Metro. More capacity is needed, if not today then surely by this plan’s roughly 2030 timeline. So more slots for more trains have to be accommodated somehow.

So Union Station must expand, but carefully. The key concern with any potential redesign must be the continued health and vitality of the historic building. Amtrak must not allow its greatest station to suffer the fate of so many of its one-time peers. Expansion is fine, but the old building must not be replaced, even in function. Supplement, but don’t take over.

Thanks to historic preservation, there is no danger that Washington Union Station will be bulldozed and replaced by a modern version, as New York’s famous Penn Station was. But there might be a danger that Washington would follow the example of Denver, where that city’s Union Station will soon be converted to a hotel, and all of its rail functions moved to new buildings directly behind the old depot.

The key demand for any expansion of Union Station must be that the original building continue to function as an integral part of the depot. Most Amtrak, MARC and VRE passengers should continue to pass through it, and the concourse facilities should be as close as possible.

It’s true that many of the rail-related functions moved out of the original building decades ago. Nevertheless, the expansions so far have resulted in a seamless whole. Casual users don’t notice where the old building ends and the new one begins. Just about everyone passes through the original depot, which still includes ticketing, and remains where most internal Union Station circulation takes place.

Any expansion must work the same way.

So how does this new plan perform?

[Continue reading Dan Malouff’s post at BeyondDC.]

Dan Malouff is an Arlington County transportation planner who blogs independently at The Local Blog Network is a group of bloggers from around the D.C. region who have agreed to make regular contributions to All Opinions Are Local.