Double-decker freeways, privatized toll roads, carpool lanes and high-speed rail are among proposed solutions for California’s looming congestion crisis, now threatened by a $140-billion transportation funding shortfall. If such projects are to be built, state officials say they must tap private funds through methods such as tolling or public-private partnerships.

California’s population of 34 million is projected to grow 60% by 2050, state officials said in a report released July 9. Travel on state roads already has increased 97% between 1980 and 2000, or about 10 times faster than new lane additions, reports The Road Information Program (TRIP), a Washington D.C.-based advocacy group.