Most of I-5 in South County will be "consistently congested" at rush hour by 2030 even if the controversial Foothill South toll road extension is built, according to the Orange County Transportation Authority's long-range transportation plan for 2006.
Environmentalists and other tollway opponents have seized on the long-range plan as a sign that the benefits of the proposed six-lane tollway do not justify sacrificing one of the state's most popular parks.
The Irvine-based Transportation Corridor Agencies, which operates a 51-mile network of tollways in Orange County, plans to build the Foothill South through the northern half of San Onofre. The park's campgrounds, wildlife areas, panoramic views and world-renowned surf spots attract about 2.7 million visitors a year.
The controversy has raged for more a decade and is unlikely to end soon. Environmentalists and the state attorney general are pursuing lawsuits to halt construction of the tollway, and it still requires state and federal approval.
"Why are we building a project with a stated purpose that won't be achieved, at the expense of our parkland?" said James Birkelund, an attorney for the Natural Resources Defense Council, an environmental advocacy group.
Opponents say the toll agency's forecasts have been unreliable in the past, leading to financial problems for the San Joaquin Hills tollway and a downsizing of the Foothill South project from eight lanes to six.
The toll agency, which is planning to build the Foothill South by 2011, has predicted that the road would help create congestion-free driving conditions on much of southern Interstate 5 by 2025. Traffic relief has been one of the project's main selling points.
Without the Foothill South, tollway officials say, travel times on I-5 from the San Diego County line to Oso Parkway — roughly 16 miles — would be an hour during peak periods in 2025 instead of 25 minutes.
"We know there's going to be more traffic on the 5 Freeway in the future," said Lisa Telles, a tollway spokeswoman. "If you don't build the toll road, there will just be more congestion."
TCA officials say that although most of their assumptions are the same, the two agencies' studies are different and thus can't be compared directly.
Now estimated to cost $875 million, the tollway extension would run from Interstate 5 at Basilone Road south of San Clemente to Oso Parkway in Rancho Santa Margarita. It would connect with the Foothill toll road after coursing through San Onofre State Beach and the Donna O'Neill Land Conservancy, a 1,200-acre open-space preserve set aside as mitigation for housing development.
Tollway officials have concluded that the route — one of eight options studied — would do the least harm to the environment and avoid the cost of condemning hundreds of homes and businesses in South County.
Dubbed the "green alignment" by the agency, the Foothill South would handle 24,000 to 52,000 daily trips by motorists in 2025 depending on the section of highway, the toll agency predicts.
"Green means Go!" the agency's promotional materials state. "Foothill-South: Your road map to traffic relief."
Like OCTA's, the corridor agency's own forecasts assume the tollway will be built as well as other improvements made to Interstate 5, including a carpool lane each way.
Tollway officials estimate that vehicle trips on I-5 would be reduced from 290,000 a day to 267,000 in the Dana Point-San Clemente area. The least benefit would occur in the Lake Forest area, where traffic would be reduced from 413,000 trips to 406,000.
The agency's studies predict that the number of congested I-5 segments would be reduced 70% during the evening rush hour, usually the busiest time of day.