It’s become a common sight on Interstate 380’s North Liberty offramps — snarled traffic.
During afternoon rush hour, a logjam of vehicles stretches down the Penn Street ramps — sometimes out onto I-380 itself, where motorists find themselves backed up onto the interstate’s shoulders.
Displaced Highway 965 motorists — forced to reroute with the highway’s nearby bridge over the Iowa River closed for emergency repairs — have added more vehicles to I-380, which is congested at the Penn Street interchange.
It is the only connection the city of North Liberty, with a population of 18,228, has to the interstate.
Cathy Cutler, transportation planner with the Iowa Department of Transportation’s District 6 office in Cedar Rapids, said additional traffic on the interstate increases the chances of collisions.
There were 58 crashes — including two fatalities — reported in June, July and August this year on the stretch of I-380 between Interstate 80 and Highway 30, according to Iowa DOT crash data.
There were 56 crashes — and one fatality — in the same span last year, and in those three months in 2014, there were 44 crashes and zero fatalities on that same length of I-380.
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“With the county’s emergency closure there on (Iowa Highway) 965 to repair that bridge, it’s pushing additional traffic out and back through what is already a bottleneck for that area,” said Nick Bergus, North Liberty communications director.
To address safety concerns and get vehicles off the interstate, North Liberty’s traffic lights on the offramps have been set for extended green lights.
But traffic woes have persisted — particularly on the southbound ramp. So discussions are underway among the officials of North Liberty, the Iowa Department of Transportation and the Metropolitan Planning Organization of Johnson County to see if additional extended green-light durations will fix the issue without causing traffic headaches elsewhere.
“The problem is, we could probably get more cars through the ramps, but they’re just going to get jammed up on Penn Street,” North Liberty city administrator Ryan Heiar said. “If we are able to modify anything, our main goal will be to get the I-380 main lane opened up.”
Meanwhile, work to expand Penn Street to four lanes — which was planned out long before the unexpected bridge closure — is nearly complete.
However, that project — from the bridge’s east side ramps to Alexander Way — cannot address the two-lane bridge, which is the bottleneck area, Bergus said.
Bergus said the city has little leeway with traffic signals, but noted there have been a few times officials manually have adjusted green light times when traffic congestion reached extreme levels.
The biggest remedy to traffic woes won’t arrive until Highway 965 bridge repairs are completed in late November.
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“When 965 bridge reopens, that will be a big boost for us,” Bergus said.
Iowa DOT’s Cutler said Highway 965 bridge’s closure has put noticeably more vehicles on the interstate, which already sees more than 55,000 average daily vehicles between North Liberty and Cedar Rapids.
“We are seeing increased traffic, and my guess would be that it’s the people that used to use 965 (and who) no longer can,” she said. “If you live south of the 965 bridge, but say north of Penn Street, you really are going to be using I-380. There’s not a whole lot of other ways to go.”
Iowa Department of Transportation auto sensor data — taken about two miles north of I-380’s intersection with Penn Street — helps show that growth. More than 28,600 vehicles traveled on I-380’s southbound lanes on May 17, before structural deficiencies were found on the Highway 965 bridge.
On May 19, Johnson County officials placed weight restrictions on the bridge and limited the structure to single-lane use, with intermittent traffic.
By July 12, I-380 traffic had reached nearly 30,000 vehicles in the southbound lanes.
The bridge — which, according to the Iowa DOT, carried more than 1,800 daily vehicles in 2014 — closed completely for repairs Sept. 6. Traffic on I-380 reached more than 32,000 vehicles that day.
Iowa DOT’s Cutler did note that traffic counts ebb and flow based on a number of variables, including seasonal changes, so that increase cannot be entirely attributed to the bridge closure.