One project would be at Pelandale Road on Highway 99 in north Modesto, the other at Sperry Road and Interstate 5, near Patterson on the West Side.
"It's fairly new for Caltrans. We normally do a more conventional interchange," said Alex Menor, a civil engineer with the California Department of Transportation.
Modesto has a couple of roundabouts, including one on La Loma Avenue. The traffic circle sparked complaints early on, but now, city traffic engineer Firoz Vohra said, "I'm only hearing good things."
Neighborhood roundabouts often are intended to slow traffic, whereas highway roundabouts are designed to increase capacity, Vohra said.
More capacity is what the city and state are looking for at Pelandale Road, where the existing interchange was built in the 1960s. Since then, several shopping centers have been developed in the area, and traffic often clogs the interchange.
Traffic signals near highway ramps on Pelandale are very close to city traffic signals at Sisk Road, which contributes to the congestion.
In mornings and afternoons, the Pelandale interchange operates at what traffic experts call level F -- when motorists can wait up to 80 seconds to get through. That is considered unacceptable by most drivers.
Continued commercial growth is likely to make the interchange even more frustrating. Wal-Mart wants to join Lowe's Home Improvement Warehouse and the Costco warehouse store at Pelandale and Sisk.
Vohra's interest got Caltrans engineers looking into the Pelandale roundabout project.
A roundabout has any number of entry and exit points. Drivers wait for traffic to clear, move into the circle, and exit where they want.
Vohra said roundabouts have been shown to reduce injury rates, traffic delays and air pollution. They also are less costly than signals.
While Caltrans is studying improvements for the Sperry Road and Pelandale interchanges, it is the Pelandale project that is furthest along. Still, construction is not expected before 2007.
In the meantime, Modesto plans to provide temporary relief. The short-term fix involves restriping Pelandale where it crosses the highway, and widening the onramps and offramps to two lanes. Work is expected to start in October and wrap up by Christmas.
The City Council approved the project contingent upon the county's approval. The Board of Supervisors is scheduled to consider the matter Tuesday.
Interim improvements will cost an estimated $966,000, with the city paying $457,000 and the county contributing $509,000, said Dean Phillips, senior civil engineer for the city.
Other highway roundabouts
Caltrans has been involved in two major roundabout projects in recent years: Donner Pass Road on Interstate 80, and one off Highway 101 in Santa Barbara.
The Santa Barbara roundabout is at Milpas Street, a major commercial corridor.
The old intersection averaged four accidents a year, said Derek Rapp, city transportation engineer. The roundabout went into use in early 2000, and since then there have been 14 collisions.
"We're not convinced that a one-year analysis is enough to draw any conclusions," Rapp said.
There have been few complaints, and the city is happy with the results, he said. The lines of traffic have been cut in half, and the time it takes people to travel through the interchange has dropped 30 percent.
Other roundabouts have been built off highways in Colorado, New York, Maryland, and all over Western Europe, Vohra said.
Bee staff writer Melanie Turner can be reached at 578-2366 or mturner@modbee.com.
