California drivers know them as the Amber Alert or traffic delay message boards. They are often blank.
CalTrans is toying with the idea, proposed by Clear Channel Outdoor, of selling advertising space on the state's nearly 700 roadside billboards.
"I think when you look at the state of California's transportation system and the need for repairs and rehabilitation to that system, we've got to figure out different ways to provide resources to accomplish that rehabilitation," said CalTrans Director Will Kempton.
High fuel prices are forcing Californians to drive less, so the state isn't collecting as much gas tax to fund road projects.
CalTrans estimates ad space could bring in tens of millions of dollars a year. But billboard opponents say California doesn't need more road distractions and visual pollution.
"This is absolutely the last thing we need. It's a bad proposal. It can compromise highway safety. It's a driver distraction," said Dennis Hathaway, Coalition to Ban Billboard Blight.
Opponents also question how effective the message boards will be if they're used for something other than a true emergency.
"A lot of people who consider outdoor advertising a form of blight tune these out," said Hathaway.
The lawmaker who wrote the bill creating the Amber Alert System says it's a great opportunity to upgrade the boards without taxpayer money.
The money could lead to upgrades like color-coded traffic alerts and the actual pictures of the child and car involved in an abduction.
"It's a much better way to engage the public in regards to those Amber Alert signs, helping them know what they are looking for," said State Senator George Runner (R-Lancaster).
California would need a federal waiver for what will be a new use of freeway signs.