Airports in Southern California, one of the nation’s most heavily populated regions, are building as much and as “green” as they can with limited space and tight budgets. Modernization projects at the San Diego, Long Beach and Los Angeles airports are requiring engineers to think creatively.

The San Diego County Regional Airport Authority’s $1-billion green-build program includes a 445,000-sq-ft expansion of Terminal 2 to accommodate 19 gates instead of nine. It also includes two new, 17,000-sq-ft curbside ticket lobbies, called smart curbs, a new transit center, an elevated departure roadway, six overpasses, and new roads and parking lots—all squeezed into a 650-acre space.