How do you go from thousands of vehicles going 50 or 60 mph on Interstate 5 to empty lanes with no traffic?

Step by step.

Freeway closures like the one that starts at 9 p.m. Friday night are planned well in advance, unlike the one that occurred earlier this month on I-5 through North Portland when propane tanks on a truck caught fire. The work will begin about an hour before complete closure.

“Think of it in terms of when we have the president coming to town (and) we have to close off the freeway and it’s done step by step by step,” said Don Hamilton, public information officer for Oregon Department of Transportation. “We close off onramp by onramp by onramp, until finally it’s closed.”

The work on Interstate 5 will begin earlier Friday evening so that the entire northbound and southbound lanes are clear of traffic by 9 p.m.

Complete list of onramps that will be closed all weekend

Here is the rundown from Hamilton:

• By 8:15 to 8:30 p.m., crews will start to slow traffic in the far-left lane, both northbound and southbound, merging traffic from three lanes to two and closing the left lanes.
• After about 8:30 p.m., crews will use cones to close the middle lanes, northbound and southbound, merging traffic into one lane, the right lane.
• By 9 p.m. all traffic will be sent off I-5, southbound at the Terwilliger Boulevard ramp and northbound at the Barbur Boulevard ramp.
• By 9 p.m. we’ll also have closed on-ramps upstream of Barbur and Terwilliger.
• The hard closure of I-5 in both directions will be in place by 9 p.m.

The freeway is expected to reopen by 5 a.m. Monday.