BLOOMINGTON, Calif. --- The California Department of Transportation recently held a press conference to highlight the safety risks posed by a growing nationwide trend: the rampant theft of copper, platinum and other metals off public roadways.

Such theft has left some traffic signals and lights inoperative, particularly in southern California's Inland Empire region. According to a report in the Los Angeles Times, thieves have also stolen guardrails and irrigation systems along streets and highways. "When you get a missing guardrail and lights and signals that don't work, that's hazardous," Terri Kasinga, a spokeswoman for CalTrans, said. "We can't get out there in five minutes and fix it."

CalTrans is asking for the public's help in cracking down on the problem, which is being fueled by the rising value of precious metals. Motorists are advised to report any suspicious behavior.

Some thieves are posing as CalTrans workers, wearing reflective vests and hard hats. One way to tell them apart from actual CalTrans workers is to check for a magnetic decal on their car, said California Highway Patrol spokesman Joe Ramos.

In April, a house in Hesperia burned down because the neighborhood hydrants were inoperative -- thieves had stolen critical copper parts. Last year, 13,800 people lost power after thieves stole parts from an Hesperia electrical substation.

Criminals are increasingly targeting copper because it can fetch more than $3 a pound at a recycling center.

Catalytic converters on cars are also commonly stolen because of the high price of platinum.