Photo by tbone_sandwich on Flickr.

Imagine we needed to evacuate downtown DC and Arlington quickly, in the middle of the day. What would be the best way to do that?

We know what wouldn’t work: telling all employees to go home at the same time. That’s pretty much what happened Tuesday after the earthquake. No bridges or roads were damaged, though some traffic signals had switched to flashing red or had lost time synchronization.

The Metro ran at 15 mph, causing huge crowds and long waits for those riding. But that couldn’t have much affected the numbers of cars on the road, since anyone who didn’t drive into work wasn’t going to drive back home.

Can our transportation network possibly move so many people at once?

Roads are a very flexible form of transportation, but are inefficient in their use of space. Each car takes up a lot of room. The New York Subway’s 22 tracks carry as many people as at least 167 lanes of car tunnels would.

If people drove evenly throughout the day, the road network would work optimally, but they don’t. Buses and trains work better for moving people in a shorter time period to a small number of locations, because they cost more to run but can fit more people in a smaller space.

There are ways to make the road more efficient. More people could occupy each car. That’s the logic behind the HOV rules and slugging on I-395 and other roads. Thanks to slugging and high bus volume, 95/395 is one of the most efficient roadways for its size in the nation (but will actually get less efficient with HOT lanes).

Instead of pushing more carpooling, VDOT actually waived the HOV restrictions on its freeways on Tuesday. That doesn’t make a lot of sense. It’s like they just threw their hands up and said, “Wow, earthquake! Let’s just ignore everything we do to make our roads work better!”

If we knew ahead of time that we’d have to evacuate DC in a hurry one day, but didn’t know when, we might actually plan for stricter HOV restrictions than usual. Take a few main arteries and make them exclusively HOV-3 or HOV-4 for the evacuation. Ask workers and residents to find “evacuation buddies” who work in the same office or live in the same inner neighborhood. These people would share the car when evacuation time came.

Once those carpools get to suburban residential areas, people will have to get home, but depending on the type of disaster, just getting everyone out might be most critical. The drivers can give rides that one time to their passengers, or they can wait in places like libraries for family members to pick them up.

Buses could also use the HOV roads, allowing them to travel much faster back to commuter lots and make a return trip to pick up even more people.

Not surprisingly, advocates for more roads and sprawl, like the Northern Virginia Transportation Alliance, immediately jumped on the issue to call for new Potomac River bridges as part of their long attempts to build an Outer Beltway. Such bridges wouldn’t actually alleviate existing traffic congestion, but would instead just drive more sprawl development and make the evacuation challenge that much harder.

During the earthquake, Ezra Klein cleverly tweeted, “This earthquake has clear policy implications that back up my previously held political opinions.” That’s certainly true for NVTA.

I actually learned something from the earthquake that doesn’t back up previously-held opinions: we can’t count on Metrorail for an emergency. Especially with today’s safety concerns, Metro is going to err on the side of limiting its operations in unusual circumstances. That’s probably the right move if it’s not a matter of life and death. But it means we need to think about evacuations another way.

We also need to think about when evacuations are necessary. Often they’re not. One of the best things the federal government can do is not to send everyone home at the exact same time. Instead, the response from OPM seems to be to pull the “everyone go home” handle at any sign of trouble. We know that this causes gridlock.

DDOT Director Terry Bellamy said at a press briefing, “You can never build your way out of an event. I know there was a lot of talk about building more bridges across to Virginia, buidling more bridges into Maryland, but you never know where the event is going to occur,” the WBJ reported.

Transportation Planning Board coordinator Ron Kirby told the Post, “Not only can [sending everyone home at once] not be done, we should not try it. … If you give [people] very good timely information, they are going to make their own decisions in ways, in general, that are going to be better for them and better for the system as a whole.”

Kirby also faults Metro for not communicating more; he might not have been on Twitter, because they actually did an excellent job of communicating there. They also sent multiple press releases out over their press list throughout the afternoon and evening. If you were at a train station or on a bus, was communication good or bad there?

The best way of all to get home after a major event like an earthquake? Walk or bike, if you can.

David Alpert is Founder and President of Greater Greater Washington and Executive Director of DC Sustainable Transportation (DCST). He worked as a Product Manager for Google for six years and has lived in the Boston, San Francisco, and New York metro areas in addition to Washington, DC. He lives with his wife and two children in Dupont Circle. Unless otherwise noted, opinions in his GGWash posts are his and not the official views of GGWash or DCST.