The large mixer truck containing about 100,000 pounds of cement crashed on the onramp from westbound state Route 52 to northbound Interstate 5 shortly before 5 a.m.

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SAN DIEGO -- An overturned concrete truck prompted authorities to shut down two lanes of northbound Interstate 5 and a freeway transition ramp near University City Tuesday.

The large mixer truck crashed on the on-ramp from westbound state Route 52 to northbound I-5 shortly before 5 a.m., according to the California Highway Patrol. The on-ramp was subsequently closed and a SigAlert was issued, authorities said.

Authorities also closed two lanes of I-5 as they maneuvered a tow truck to right the overturned truck. The closures caused a major backup on northbound I-5 during the morning commute.

The cause of the accident is under investigation.