Update below: MTA says it's up to the city of Los Angeles to decide whether to allow trains to preempt vehicle traffic, and L.A. has decided not to.

The Expo Line will open all the way to Santa Monica on May 20, connecting downtown to the beach via public transportation for the first time since the 1950s.

The Metropolitan Transportation Authority says the ride will take 46 minutes — though maybe more like 48 minutes under real-world conditions. They argue that will be a vast improvement over travel times on the 10 freeway. (Ask any MTA official, and they'll tell you the last time they drove to Santa Monica it took 80 or 90 minutes.)

But is it, in fact, a significant improvement? Inrix, the traffic-monitoring service, recently came out with its scorecard of the most congested corridors in the country. During peak hours (6 to 10 a.m. and 3 to 7 p.m. weekdays) it took 39 minutes, on average, to go the 15 miles between 20th Street and Alameda Street.

That's not the exact same starting and ending point of the Expo Line — but it's close. The train will run 15.1 miles from Fourth Street and Colorado Avenue to Seventh and Flower streets. Because we don't have better traffic data, let's call it roughly comparable.

So: 39 minutes, on average. Now, traffic can also be much worse than the average. Inrix found that on Wednesday at 5 p.m., it takes 73 minutes. It can also be much better. When there's no traffic, you can do the same distance in 15 minutes.

Of course, when you're in a car, you have to find a place to park, and that takes time — maybe more time than it takes to wait for a train. So this is not a door-to-door comparison.

Still, the point is that the train is going to have to compete to win over passengers, and it's not a slam-dunk case that it will be faster than driving on the 10. If traffic is really bad, then yes. If it's good, then no. And if it's a normal commuting time, then, well, maybe.

Is there anything that could be done to shave a few minutes off the train's 48-minute travel time? As it happens, there could be. The Expo Line currently runs pretty fast between Culver City and Western Avenue. But east of there, as it gets into USC and especially downtown, it starts to bog down. The segment between Vermont and Seventh Street is about 30 percent of the distance between Culver City and downtown, but it takes 50 percent of the time.

The train runs at street level through downtown, and it stops for cross traffic, almost like a bus. It's not uncommon for the train to sit at Jefferson Boulevard, or Adams Boulevard, or 23rd Street, or 18th Street, or 12th Street, for 20 or 30 or 40 seconds waiting for the light to change. It's not as if these are all major thoroughfares. At USC, the trains stop at Watt Way, which is a campus entrance road, and at Trousdale Parkway, a pedestrian crossing.

To a transit advocate, this is craziness. Why should a three-car train, with maybe 250 people on it, sit and wait for vehicle traffic, which carries 1.1 persons per car?

The solution to this, in their view, would be “signal preemption” — a gated crossing where traffic must stop to allow trains to pass. This has been done on many of the intersections on the Santa Monica extension. Could it be done downtown as well?

“Gated crossings are very much more expensive,” says Sean Skehan, a longtime engineer for the L.A. Department of Transportation. When the line was being built, he says, “That's what drove the effort. On Expo 2, they decided to spend a little more money and get improved transit performance.”

Preemption also would disrupt traffic downtown, he says, and there's a question about whether the intersections would be big enough to accommodate gates. For now at least, it's off the table.

In the absence of preemption, the traffic signals give “priority” to the trains. If a train is coming, the signal might hold a green a little longer to let it through.

“If the train driver is good, he can catch some of the greens,” says Gokhan Esirgen, a transit advocate. “If he is slow by 5 seconds, he will miss all greens.”

The lights are timed based on MTA's estimate that trains will stop for 20 seconds at each station. However, stops usually take longer than that, which means they may miss a green light.

Esirgen believes the problem could be overcome with sufficient political will and a change of mindset at the DOT.

“They only care about cars,” he says.

The DOT, however, argues that even with preemption, the trains would still face a bottleneck in downtown. Blue Line trains and Expo Line trains converge at Washington Boulevard, and sometimes Expo trains have to be held back to allow Blue Line trains to pass.

“We’re not opposed to changing the timing to further improve the situation,” Skehan says. “We’re not here standing up for the car driver. We want to keep everything moving.”

Update at 2:57 p.m. Monday April 18: Esirgen points out that the DOT could provide signal preemption without gates — but that it has chosen not to do so. Faced with the same choice, the city of Santa Monica opted to provide preemption without gates.

“The local jurisdiction decides what it wants,” says Paul Gonzales, an MTA spokesman. “LADOT does not favor preemption. Santa Monica has a different viewpoint. We work with both cities to accomplish goals, even though on this issue their viewpoints are a bit different.”

Esirgen points out that the DOT could change its mind, if there were enough political pressure to speed up the train.

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