Most highway projects have gradual results, but the permanent closure of the Cabrillo Boulevard on-ramp to Highway 101 will have a sudden effect on drivers.

The southbound on-ramp will be closed permanently as soon as Aug. 3 and may not be replaced with another.

The ramp closure is part of a four-phase project to ease congestion in the Highway 101 corridor from Milpas Street in Santa Barbara to Mussel Shoals in Ventura County. The project is led by Caltrans and is primarily sponsored by the Santa Barbara County Association of Governments.

Closing the left-hand on-ramp is necessary because of space constraints, given the addition of a lane in both northbound and southbound directions, and to eliminate conflicting traffic movement on the highway, said Gregg Hart, SBCAG public information and government affairs coordinator.

The added lane eventually will become a carpool lane, and having left-hand entrances onto the freeway would become problematic, Hart said. There would be too many conflicting traffic patterns and lane changing, which can lead to congestion, he said.

Also, some drivers use the Cabrillo entrance to skip the queue that backs up through downtown Santa Barbara, and eliminating the ramp should keep traffic flowing, he said.

“We’re pretty confident this is going to work,” he said.

However, those involved with the project are looking at the option of adding a right-hand on-ramp at Cabrillo farther along in the project, but the environmental impact report would have to be conducted first. Right-hand on-ramps aren’t as much of a congestion issue since they don’t often slow down the fast lane, he said.

“There’s not enough funding to solve the Cabrillo on-ramp issue with one phase,” Hart said.

The $53 million phase one area under construction includes adding lanes between Milpas and Hot Springs Road and adding a roundabout at the confluence of Cabrillo, Hot Springs, Coast Village Road and Old Coast Highway.

Hart said the additional southbound lane will not be a carpool lane until there’s enough length of road to justify it, possibly not until the entire 13.3-mile project is completed.

“It doesn’t work for (carpool lanes) to be in two-mile chunks,” he said.

Additional ramp changes include a new Milpas off-ramp.

It’s possible the Sheffield Drive left-hand southbound on-ramp, near Summerland, also will be closed since hilly on-ramps cause drivers to slow down while trying to merge into the fast lane, Hart said.

The roundabout construction is about a third done and will be functional in a few months. The detours have to be integrated and part of Coast Village Road must be closed during construction.

Its slated completion date is in November, but some aspects of the project have finished ahead of schedule.

— Noozhawk staff writer Giana Magnoli can be reached at gmagnoli@noozhawk.com.