The carpool lane on the southbound 405 through the Sepulveda Pass. Photo by Matt Pagel, via Flickr.

For all the hype and talk about this weekend’s upcoming 405 closure — aka Carmageddon — I’ve also been a little surprised there hasn’t been more discussion of a pretty basic question: is the 405 project really worth the hassle of closing the freeway?

I think so.

The I-405 Sepulveda Pass Improvements Project may not be a panacea for all that ills the oft-congested 405. But I think it’s certainly better than the status quo, which most reasonable people would agree is pretty bad — unless you’re really into mind-melting, greenhouse gas-spewing traffic jams.

The project’s big ticket item is the addition of 10 miles of carpool lane on the northbound side of the 405 to match the carpool lane that has already been built on the southbound side (don’t ask why they weren’t built at the same time). The project is also realigning and/or expanding 27 on- and off-ramps on the 405 between the 10 and 101 freeways and widening bridges over the freeway, including the Mulholland Drive Bridge that is being partially torn down this weekend.

In my view, the ramp improvements are a vastly under-rated part of the project. One of the ironies of our freeway system is that it’s intended to get people where they’re going in a speedy fashion. But throughout So Cal, the junction of freeways and surface streets often causes significant traffic disruptions because of all the cars trying to get on and off the freeway.

It’s a particularly noxious situation on the Westside where surface streets carrying freeway-like volumes of traffic. Better ramps and traffic signals and wider bridges over the freeway should improve that situation.

But the real hot-button issue with the 405 project is the addition of the carpool lane.

It’s generally agreed (although there are certainly skeptics) by most engineers that at peak hours carpool lanes can carry more people than a regular traffic lane. The reason is obvious: There are more people per vehicle in the carpool lanes.

Speed is a separate issue. As anyone knows who has driven a local freeway during the height of rush hour, the carpool lane can — and often does — get as congested as the regular lanes.

The idea behind carpool lanes is to offer greater speed as an incentive for people to carpool. So it’s not a good thing when traffic in those lanes slows down. That said, the carpool lane is still partially succeeding by carrying more people than the other lanes — at least at some hours. If there is only so much room to build freeways, that’s a good thing.

I also suspect that over the course of the day, most carpool lanes offer faster trips than do the regular lanes, particularly in the busier freeway corridors. The reason is simple: as critics of HOV lanes often note, the lanes are not always at full capacity — meaning there’s room to actually drive.

“I don’t think of this as just a local project for the 405,” says Borja Leon, the Deputy Mayor for Transportation for Mayor Antonio Villaraigosa. “It’s really a regional project. Once we put together a regional carpool lane network, it really starts giving more options for those trying to carpool from point A to point B anywhere in the region.

“If there is a real network of carpool lanes, people will start believing in it and will consider it as an option,” Leon added.

The good news on that front is that there are now more than 500 miles of carpool lanes in L.A. County — there was just 58 in 1993 — and more are on the way. However, on the down side, there are still key corridors without them, including the Santa Monica Freeway and the Ventura Freeway.

Carpool lanes aren’t just used by carpoolers. Buses and van pools use them and may use them more as more lanes are built. There is also the option to manage the lanes differently in the future to make them as effective as possible.

Of course, if you don’t have a carpool lane to begin with, you also can’t manage it differently.

For example, the Metro ExpressLanes project is turning the carpool lanes on parts of the 10 and 110 freeways into so-called HOT lanes in which single occupant vehicles can use extra capacity in the lanes in exchange for a toll. It’s an experiment. But it has worked in other places and it makes sense to spread traffic better around all of a freeway’s lanes.

The other point I want everyone to consider is that the 405 carpool lane and other improvements is hardly the end of the story for the 405 corridor. The Measure R sales tax increase approved by L.A. County voters in 2008 included more than a billion dollars in funding for a transit project to connect the Westside and San Fernando Valley via the Sepulveda Pass.

Formal studies have yet to begin, but when they do, many transit options will undoubtedly be considered and scrutinized. It doesn’t take much imagination to guess what some might be. Enhanced bus service in the corridor. A subway. Maybe even — just to be pie in the sky — a tunnel with toll lanes and rail or bus lanes.

As someone who moved to the L.A. area in 1994, I can’t even begin to offer a rationale explanation of how it got to be the year 2011 without a serious transit option through the Sepulveda corridor. I do know, as has been widely discussed in recent weeks, that Carmageddon likely wouldn’t be the big hoo-ha that it is if such transit service existed.

And here’s the thing: that transit project won’t exist any time soon unless Congress gets serious about helping local areas build transit. The America Fast Forward program could do that if — and it’s a big if — the Congress and President Obama make it law as part of the next big transportation spending bill.

As for this weekend of traffic inconvenience, it will pass. In the cosmic scheme of things, think of it this way: the freeway has been open pretty much nonstop for nearly 50 years and there are very few other pieces of public infrastructure that can stand that kind of daily beating without shutdowns.