The crash occurred at about 12:15 a.m. In all, three big rigs and three regular vehicles were involved in the wreck. Two of the big rigs overturned.
The accident occurred on the two-lane underground transition from the eastbound 210 Freeway to the eastbound 134 Freeway, resulting in the closure of a portion of the eastbound 210.
The CHP says a big rig driver reportedly lost control in the tunnel and a second big rig driver tried to get out of the way. There were three other passenger cars inside the tunnel at the time, and they all collided.
The driver of the first big rig was killed. Two people in the passenger cars were injured. According to the CHP, not long after the five vehicles collided, a third big rig entered the tunnel.
"A third commercial vehicle -- a UPS truck -- came through in the No. 1 lane. He saw what was going on and avoided most of it but the trailer portion of his rig was struck by the original big rig," said Sgt. Ernie Amaya with the CHP.
CHP officials are trying to figure out exactly what led up to the crash.
"They're trying to recreate the scene and the sequence of events, so they'll be taking a lot of measurements and it'll take them quite a bit of time," said Ming Hsu with CHP.
CHP officials said the transition road reopened shortly after midnight Friday, 24 hours after the crash.
Another big-rig fatality occurred a few hours later shortly before 3 a.m. about four miles east on the eastbound 210 Freeway. A big rig struck the freeway center divider, spreading debris into the nearby Gold Line tracks. Officials said a 33-year-old Moreno Valley man died in the crash.
This crash prompted multiple lane closures at Madre Street, as well as the closure of the Metro Gold Line between Pasadena's Allen and Sierra Madre Villa stations, according to Metro officials.
The wet weather caused lots of problems for drivers across the Southland, making extra work for law enforcement.
"It's been a nightmare, but it's our job. We come out here and we're handling it one at a time. Just in our area alone, we had three major traffic collisions," described CHP Officer Ernie Amaya.
In the Glendale-Burbank area, a semi hit the center divider and broke through the concrete barrier on the northbound 5 Freeway at the 134 Freeway. The crash sent debris into the southbound lanes of traffic.
In another wreck, a big rig jackknifed on the westbound 210 Freeway to the westbound 210 connector in Pasadena. No one was hurt, but traffic was brought to a standstill.
City News Service contributed to this report.