Jackson County motorists may need an extra jolt of coffee for their Monday commute as they encounter a bewildering number of ways to enter Interstate 5 in south Medford.

Jackson County motorists may need an extra jolt of coffee for their Monday commute as they encounter a bewildering number of ways to enter Interstate 5 in south Medford.

For about two days, there will be a total of three possibilities to get on the freeway if you're heading southbound, marking completion of another phase of the $70 million south Medford interchange.

The Oregon Department of Transportation will open the new southbound on-ramp from Garfield Street Monday morning, but leave the existing entrances to the freeway at Barnett available for two days before they are closed permanently Wednesday.

ODOT spokesman Gary Leaming said it will take some time for motorists to get used to the new entrance at the interchange, so ODOT decided it would be best to leave the old on-ramps open.

"We know there will be some confusion," he said. "There always is when you open a new road."

After the two existing on-ramps are closed, southbound motorists can enter the freeway off Garfield Street, accessed either from Highway 99 or Center Drive.

General contractor Wildish Standard Paving of Eugene will demolish the old on-ramps to allow for completion of the new freeway exit at Garfield that is scheduled to open in late March.

The final portion of the interchange that will provide a northbound entrance to the freeway will open in May.

Starting today, 40 trucks will pour 325 cubic yards of concrete that will provide the surface for the main span on the interchange where it crosses Interstate 5.

To make sure traffic flows as smoothly as possible during the construction, southbound motorists who exit at Garfield in March will be able to turn left toward Highland. Other traffic won't be allowed over the interchange bridge until the northbound entrance is completed and the traffic signals are installed.

On Wednesday, workers poured concrete barriers and folded up tarps as they tried to get the new southbound entrance ready for Monday.

Sean Dawe, senior project inspector for ODOT, told workers they would have to clean out drains before the roadway is put into service.

All the drains on the freeway are designed to flow into a bio-swale, or collecting pond, that helps filter road runoff.

"Most of the effluent coming off the freeway is highly contaminate-laden," said Dawe.

He said the drains needed to be cleaned out because they have collected debris during the construction process.

ODOT will give motorists plenty of visual clues to alert them of the changes around south Medford.

"Watch the signs, and watch the cones," cautioned Leaming.

Reach reporter Damian Mann at 776-4476 or dmann@mailtribune.com.