A half-cent-on-the-dollar sales tax would be extended for 30 years if voters OK a plan to fund transportation projects in Southern California.

The Orange County Transportation Authority took the first step Monday, Oct. 24, toward coming up with a ballot measure that would ask voters to extend the tax to pay for road and bridgework.

Extending the tax would bring in a projected $12 billion, the Los Angeles Times reported. The revenue would be used to make additional improvements to the Santa Ana and Riverside freeways as well as the “Orange Crush” interchange where highways 57, 22 and 5 converge.

The sales tax, approved by voters in 1990 as Measure M, is expected to bring in more than $4 billion by the time it expires in 2011. It has accounted for at least a quarter of all money used to pay for transportation in Orange County.

The sales surcharge has helped pay for widening parts of highways 57, 22, 55, 91 and 405 as well as a stretch of the Santa Ana Freeway.

Officials with the agency said a ballot measure extending the surcharge could come before voters as early as next fall.

If an extension is approved, the authority’s board told the Times that highways, streets and transit projects would continue to get the same share of Measure M money. Currently, freeways get 43 percent while streets and roads receive 32 percent and transit takes 25 percent.

The agency plans to hold meetings to gather public opinion.