If you haven't heard, we're expecting a little traffic here in west Los Angeles this weekend. Actually, we're expecting it all over the city. No, wait. All over the county. 

Forget it. The entire state is going to be paralyzed. Now everybody freak out!

I am writing, of course, about the two-day closure of Interstate 405 between the 101 and 10 freeways, otherwise known as "Carmageddon." This weekend, LA Metro turns off the busiest freeway in the country, like Niagara Falls running dry. 

The stanching of the flow of 500,000 cars daily will be a grand experiment in transportation planning and public relations, and as far as I'm concerned, there's not a single credible hypothesis. I'd like to think that I have special insight into what's going to happen because I live a two-minute drive from Ground Zero--the Sunset exit of the 405, where the cascade of cars from the Valley splashes down into the pool of gridlock that is the Westside--but I don't have a clue about whether this will be a blessing or a curse. 

It's quite likely the parallel routes to the 405 will be stuffed. I wouldn't drive Topanga, Coldwater, or Laurel canyons for all the oil in Saudi Arabia. The 101 and the 5 are likely to absorb traffic well beyond their carrying capacity. 

But it's the broader network effects that are going to be most interesting. For instance, if drivers want to get to Century City but take the 101, does that mean that all the east-west streets between Hollywood and Century city are going to be clogged?  Will through-traffic -- from, say, Santa Clarita to LAX, or even San Francisco to San Diego -- have to make massive detours, thus backing up the entire statewide freeway system? 

Or will most people just stay home and fire up the grill? 

Carmageddon has elicited some hopeful proclamations from folks who say that it presents a great opportunity to stay home, hang out with local friends, smoke a few joints, and contemplate the lamentable role of the automobile in modern life. I'm all for it. But I'm not sure that people who have to work Saturday and Sunday feel the same way. 

However fun or inconvenient it may be, all the speculation about Carmageddon weekend ignores important questions that policymakers may have missed in their original cost-benefit analyses. For sure, the improved freeway will be better than the old freeway. But you can't compare the new and the old. You also have to consider the costs that we have incurred in between. 

If you haven't seen the construction site, you'd be amazed at what's already been going on for two years. This isn't Texas, where another lane just requires laying down another strip of asphalt. And it's not even the San Francisco Bay, where you can build a new bridge right next to the old one. 

We're talking about demolishing houses. We're talking about cutting 200-foot-high chunks off hillsides and replacing them with retaining walls. They're tearing bridges down one half a time, so traffic can squeeze past until they rebuild them whole (that's what they're doing this weekend). On- and off-ramps have been jury-rigged. Lanes on surface streets have disappeared. 

In short, Carmageddon may be arriving this weekend, but we've been on a highway to hell for as long as this project has been underway. 

Everyone, save a few transportation planners, is familiar by now with the arguments about induced demand. Once the lanes are added, they could fill up almost instantly. But that's only half the problem with freeway construction. 

The other half--which is never mentioned or measured, as far as I know--is the time and money lost to drivers while the freeway is being improved. Even if the 405 doesn't clog up instantly and does flow freely for a few years after the project is finished, I find it hard to believe that the time savings will compensate for all the time lost during its construction. 

To whit, a 1.5-mile drive from my apartment to Westwood, via Wilshire Boulevard, that can take five minutes can now take over a half-hour. Walking is literally faster. Multiply that by the tens of thousands of other drivers who take that route daily. Then multiply it by the other chokepoints. We'd all need Buggatis and open roads for years in order to make up for what we're now enduring. 

Then there's the pollution. One of the arguments in favor of carpool lanes is that commuters consolidate their vehicles and that they'll pollute less because they're flowing freely. But the cars stuck on Wilshire are now polluting more. Again, unless every car stuck in traffic on the new 405 runs on hydrogen and fairy dust, the construction alone will have caused a net increase in pollution. 

In other words, by the time this thing has a chance to reduce pollution and traffic--if it ever does--it will already have generated plenty of pollution and traffic. 

So who benefits from this feat of engineering? I know that a certain construction firm is reaping $1 billion in revenue. But I'll get something more sublime. On Saturday evening, perhaps near sundown, I get to stroll across the Sunset bridge, peer into the twilight, and see, for once, what an empty freeway looks like. 

--Josh Stephens

Updated 15 July 1pm.