On a Saturday morning trip to downtown Los Angeles, a Metro Expo Line train pulled out of a station in Exposition Park, its three cars filled with passengers.
Traffic signals along Exposition Boulevard turned red, and lights flashed to signal the approach of the train, which had "watch for trains" printed in yard-high letters on the front car.
But the warnings weren't enough.
Just before 11 a.m., a driver in a silver Hyundai sedan turned left across the tracks toward a USC campus gate and collided with the train. The crash pushed two of the Metro light-rail cars onto Exposition and left 12 people hurt, one critically.
The crash is renewing a decades-long debate about whether more safety measures are needed in Los Angeles County's growing rail network where drivers, pedestrians and light-rail trains share the roadway.
Three of the Metropolitan Transportation Authority's six rail lines sometimes run along surface streets, and collisions at crossings are not uncommon: Saturday's crash is at least the 18th in the last 12 months between Metro trains and cars, according to a survey of agency service alerts and news reports.
At least four of those occurred on the Expo Line. But it's the Blue Line that has raised the most concerns. The route between downtown L.A. and Long Beach has seen more than 120 people die in accidents involving either pedestrians or drivers since it began service in 1990, making it one of the deadliest light-rail lines in the United States.
How best to protect drivers and riders has taken on new importance as Metro faces a record building boom: Of the five rail lines currently under construction, three will have at-grade sections running through neighborhoods in the San Gabriel Valley, South Los Angeles and the Westside.
"Building more light rail is not a bad thing, but we need to do a better job of ensuring that it's safe," said Najmedin Meshkati, a USC engineering professor who studies rail safety and has criticized the design of crossings along the Expo Line, which links downtown Los Angeles to Culver City and will begin service to Santa Monica sometime next year.
The Expo Line cars involved in Saturday's crash were wrapped in vivid yellow banners with large lettering reading, "Hear bells?" and "Heads up, watch for trains" — part of a recent public awareness campaign to reduce collisions along portions of the 87-mile Metro rail network.
Brightly colored banners and flashing lights are better than nothing, Meshkati said, but the only way to protect pedestrians and cars from trains is by separating them, either with crossing arms and gates, or train tracks that run under or above traffic.
Metro trains run through tunnels and on overpasses in some areas, a decision the agency makes based on the geography of the street and the surrounding area. But separating tracks from traffic is often cost-prohibitive, Metro spokesman Marc Littman said.
Surface-street crossings are safe when drivers and pedestrians follow traffic signals, Littman said, adding that, "All over the world, there are trains operating safely in dense, urban areas. You can't build a bubble around the rail system."
Meshkati said that while that may be the case, it's easy for pedestrians and drivers to get confused in unfamiliar areas or after dark, so Metro should aim to make intersections as foolproof as possible.
During the Expo Line's design process, Meshkati and five other academics recommended including gate arms that block off all lanes of traffic in both directions as trains approach. So-called four-quadrant arms prevent drivers from maneuvering into the opposite lane and trying to beat the train.
Along Exposition Boulevard, trains run down a broad median, separated from traffic by a wrought-iron fence. Traffic signals remind drivers not to turn into the path of a train. But the wide intersection where Saturday's crash occurred does not have gate arms.
After the Expo Line began service in 2012, Meshkati sounded the alarm again, saying three crossings along the 7.9-mile route were "woefully inadequate." Those intersections didn't include the crossing near USC and the Exposition Park Rose Garden, where Saturday's crash took place, but, he said, he wasn't surprised.
Accidents between cars and Metro trains tend to be less severe than crashes involving commuter rail lines such as Metrolink, because light-rail trains weigh less and travel at slower speeds. Still, the crashes sometimes cause significant damage: Last March, a dozen people were sent to the hospital after a minivan driver pulled into the path of an oncoming Metro Blue Line train.
Derailments on the Metro system also are rare, Littman said. In 25 years working for Metro and its predecessor agency, he said he could recall "less than a handful of times" when a crash involved a derailment, but the "impact was strong enough" to cause one Saturday.
Any statistics about crashes must be put in perspective, Littman said, emphasizing that crashes with cars can range in severity from "a clipped mirror" to what happened Saturday. He added that the rate of crashes is relatively low, given the hundreds of thousands of miles that Metro trains cover per year.
Major grade-crossing projects, such as building an overpass, can cost more than $20 million, a price-tag that poses difficulties for transportation agencies across California.
Since a series of deadly accidents a decade ago, Metrolink has pushed to make improvements to the 451 street-level crossings in its six-county system. But some funding disparities remain: The Ventura County crash last month that killed a Metrolink train operator occurred at a grade-crossing that had worried regulators in the past. A $30-million grade separation planned for the Rice Avenue crossing, which saw three accidents in the five years before February's crash, languished without state and federal funding.
The cause of Saturday's Metro crash and related factors, including speed, are still under investigation. The speed limit along Exposition near USC is 35 mph for both cars and trains, but the train had just pulled out of the station and was probably not going that fast at the time of the crash, Metro officials said.
Times staff writers Jack Dolan and Jason Song contributed to this report.