The US Federal Highway Administration (FHWA) has announced a $421m loan for the SR 91 Corridor Improvement Project in Southern California.

The loan is to be provided to the Riverside County Transportation Commission (RCTC) under the Transportation Infrastructure Finance Innovation Act (TIFIA) loan programme.

The project will increase the capacity of the corridor, while lowering congestion on the Riverside County side of the highway.

US Transportation Secretary Anthony Foxx said: "This project is a job creator that will improve mobility in the region and better connect Orange and Riverside counties."

Under the project, SR 91 will extend the existing two 91 Express Lanes and build one general purpose lane in each direction from the Orange County line to I-15 in Riverside County, a distance of around eight miles.

The project also includes upgrades to bridges and intersections, and the addition of merge lanes for improved access.

It is being advanced by the RCTC under an agreement with the California Department of Transportation (Caltrans) to toll the new lanes for 50 years.

"The project will increase the capacity of the corridor, while lowering congestion on the Riverside County side of the highway."

Currently over 280,000 vehicles use SR 91 Express Lanes every day and it is the only freeway linking the Riverside and Orange counties, which together have a population of 5.3 million people.

Population growth in western Riverside County and increased employment opportunities in Orange County have led to increased congestion on SR 91.

Federal Highway Administrator Victor Mendez said that the programme will ease congestion and makes travel easier.

"It will improve quality of life and strengthen the local economy," Mendez added.

The TIFIA loan programme is created to fill market gaps and leverage substantial non-federal investments.

Each dollar of federal funding can provide up to $10 in TIFIA credit assistance and support around $30 in transportation infrastructure investment.

Since its launch, the programme has provided assistance to 33 projects and turn $11.6bn in DOT assistance into $44bn in infrastructure investment across the country.