SAN DIEGO -- Repairs to a water main that ruptured underneath a Carmel Valley thoroughfare overnight kept one side of the street shut down through the day Friday, creating heavier-than-usual traffic and sending motorists over detour routes.

The failed 16-inch-diameter plastic pipeline began flooding the intersection of Carmel Mountain Road and Torrey View Court, just east of Interstate 5, shortly before 10:30 p.m. Thursday, the San Diego Water Department reported.

The break left numerous nearby apartments and condominiums without water for about an hour, but no buildings flooded, said SDWD spokesman Arian Collins.

Crews shut down the eastbound side of the street at Torrey View Court to allow for repairs. Officials hoped to have one of those lanes reopened by late afternoon and the pipeline and street both fully patched by late evening, Collins said.

The spokesman said it was unclear why the main, which is less than 10 years old, failed. Most of the water-service pipelines that rupture in the city are corroded cast-iron ones dating back three to five decades or more.

"We don't know what the problem was," Collins said. "We're going to be evaluating it (next) week to see why it broke. We don't have many problems with PVC pipe."