Diverging diamond intersection planned for Parmer Lane, I-35


In an effort to relieve bottlenecks on Parmer Lane at I-35, the Texas Department of Transportation plans to convert the interchange to a diverging diamond intersection.

DDIs temporarily shift traffic to the left side of the roadway to facilitate better left turns and through traffic. TxDOT implemented a DDI in Round Rock at RM 1431 and I-35 near IKEA, and TxDOT spokeswoman Kelli Reyna said the intersection changes have helped to decrease the number of traffic accidents.

TxDOT hosted an open house Tuesday for residents to view its plans for $25 million worth of intersection improvements at I-35 and Parmer Lane and $3.2 million of ramps improvements on I-35 between Grand Avenue Parkway and SH 45 N in Pflugerville.

Construction could begin on the I-35 improvements in late 2018 and be complete in summer 2020.

I-35 and Parmer Lane

North Austin resident Russ Nettles (in hat) asks questions about the proposed changes to Parmer Lane and I-35 during a Dec. 6 open house event. (via Amy Denney/Community Impact Newspaper)

Parmer upgrades

Besides adding a DDI on Parmer, TxDOT plans to reconstruct entrance and exit ramps on I-35 south of Parmer, build right turn lanes at Parmer and Lamar Boulevard and add a dual left-turn lanes from Parmer to Lamar.

North Austin resident Miriam Moorman said the proximity of the Parmer and Lamar intersection adds to the congestion in the area because of drivers weaving on Parmer from I-35 to turn either north or south on Lamar.

“I think it’s really dangerous,” she said. “I’m surprised there are not more accidents. For the most part it looks like [the DDI]will help with congestion.”

I-35 and Parmer Lane

In a diverging diamond intersection drivers temporarily cross to the left side of the road to either turn left or pass through the Parmer Lane intersection. Drivers wanting to go straight on the frontage roads would take the bypass lane highlighted in blue. (via Courtesy TxDOT)

Drivers wanting to pass through the intersection at Parmer on the I-35 frontage road will need to take the bypass lane to avoid the light. An existing bypass lane opened in September 2014 on the northbound frontage road, and TxDOT plans to also build a new bypass lane on the southbound side.

But eliminating the through traffic on the frontage roads has some residents concerned, including Moorman and North Austin resident Russ Nettles who lives and works near the I-35 and Parmer Lane intersection.

“There’s no on ramp to southbound I-35 from Lowes,” he said. “The traffic has to go through the intersection.

Even with adding a bypass lane on the southbound I-35 frontage road, Nettles said he is concerned that lane will create more congestion on the frontage roads. He said it is already hard to access businesses in the Tech Ridge shopping center anchored by Sears because of the existing northbound bypass lane—Target closed its Tech Ridge store in January—and he said the addition of the DDI will make accessing area businesses worse.

“I think this is going to be a disaster,” he said.

He said TxDOT should consider adding a second left-turn lane at the light on Parmer at Center Lake Drive to allow drivers to make U-turns more easily and head westbound on Parmer or north on I-35.

An online open house is available through Dec. 20 at www.mobility35openhouse.com.

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Amy Denney
Amy has been reporting in community journalism since 2007. She worked in the Chicago suburbs for three years before migrating south and joined Community Impact Newspaper in September 2010. Amy has been editor of the Northwest Austin publication since August 2012 and she is also the transportation beat reporter for the Austin area.
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