|
Aug. 27, 2020
Defining the trunnion: a look inside the Interstate Bridge project
Get ready because we're now just two weeks away from the Sept. 12-20 closure of the northbound span of the Interstate Bridge
Crews at work on the northbound span's south tower to prepare for the Sept. 12-20 closure of the northbound lanes.
The trunnion replacement
Just what is a trunnion? The trunnion is an axle located at the center of each wheel that helps lift and lower the bridge. The wheels, also called sheaves, are part of the pulley system that raises and lowers the lift span of the Interstate Bridge. The trunnion and sheaves are just two of the parts being replaced Sept. 12-20 on the south tower of the northbound span of the Interstate Bridge.
 Left: The trunnion fabricated in 1997 to replace the original 1917 part in the north tower of the northbound span. Right: The trunnion fabricated in 2020 to replace the part in the south tower of the northbound span. In 2020, the trunnion arrived already attached to the sheaves.
About the bridge components: by the numbers
6.5 miles
The length of the pulley cables in both spans that need oiling and greasing each year.
12 feet
The diameter of the sheaves, the big wheels in the pulley system that wind up the cable during a bridge lift. We’re bringing two new sheaves to the south tower.
20 inches
The diameter of the trunnion.
103 years
Age of the northbound span.
760 tons
The weight of counterweights at the top of the bridge used to balance the weight of the road deck during lifts.
2,425 miles
The distance replacement parts traveled from fabrication at G&G Steel in Russellville, Alabama to the Interstate Bridge.
|
Top: A view of the inner workings of the bridge with gears and cables visible.
Middle: The new sheaves, ready for installation.
Bottom: The Interstate Bridge soon after its opening in 1917 with the ferry adjacent.
Watch for traffic pattern changes
Everyone crossing the Interstate Bridge will need to be extra careful before, during and after the Sept. 12-20 closure of the northbound span.
Traffic patterns will be new and unfamiliar. The speed limit will drop to 40 mph.
For those nine days, the three-lane southbound span will carry all traffic in both directions, with two lanes open southbound in the morning and two lanes northbound open in the evening. Northbound drivers will shift over to the southbound span before the Interstate Bridge and changing back to the northbound lanes coming off the bridge.
The sidewalk on the northbound span will also close. A signed detour will direct people biking, walking and rolling to the southbound sidewalk, with flaggers available to help point the way.
Work zones always present extra hazards for drivers but the Sept. 12-20 closure offers unique complexities.
|
Upcoming traffic impacts
Aug. 28: Overnight closure of northbound bridge
All lanes of northbound I-5 will close at the Interstate Bridge from 12:01 to 2 a.m. Friday, Aug. 28. Travelers can take I-84 east to northbound I-205 as a detour into Clark County. Bikes and pedestrians should follow the signed detour to use the sidewalk on the southbound Interstate Bridge span.
Sept. 12-20: Nine-day closure of the northbound span
At 12:01 a.m. Saturday, Sept. 12, crews will begin closing the northbound span of the Interstate Bridge, which will remain closed until 11:59 p.m. Sunday, Sept. 20 while crews replace mechanical parts that help raise and lower the bridge.
During the nine-day closure, northbound and southbound traffic will share the three lanes and sidewalk on the southbound span. Movable concrete barriers will allow two lanes of traffic in the busiest direction, with two southbound lanes open for the morning commute and two northbound lanes open for the afternoon commute.
The sidewalk on the southbound span will remain open at all times for people walking or riding bicycles.
Sept. 21-27: Lane closure on I-5 south
The left lane on the southbound span will close Sept. 21-27 around the clock as crews upgrade the median barrier, remove equipment and wrap up the project.
Other impacts
Before and after the September closure, travelers should expect occasional night lane closures on I-5, up to 30-minute bridge lifts on the northbound span and nighttime ramp closures between Victory Boulevard in Portland and SR 14 in Vancouver.
Learn more
- Go to InterstateBridge.org, the project web site, for maps and detour directions, bike and pedestrian information, travel strategies and other project details.
- Check TripCheck.com for real-time traffic updates.
-
Visit our Flickr for video and photos.
|
