AUSTIN (KXAN) — A diverging diamond interchange or DDI is an infrastructure design that temporarily shifts traffic to the left side of the road and allows left-turn drivers to move without having to wait on a left-turn signal and traffic to continue flowing.
In Central Texas, there are three diverging diamond intersections with the most recent opening in October 2021 at the intersection of Interstate 35 and Parmer Lane in north Austin.
“The interesting thing about DDIs is they can generally be built within the same footprint of the existing intersection so you don’t have to acquire additional right-of-way – that makes it financially feasible,” explained Brad Wheelis, a spokesperson for TxDOT.
The first DDI opened up about six years ago in May 2016 in Round Rock at I-35 and University Boulevard. Followed by a second DDI around three years ago in south Austin at MoPac and Slaughter Lane.
This design remains a fairly new traffic pattern for many drivers with the first-ever diverging diamond intersection in the country opening up in 2009.
TxDOT says the design not only addresses congestion but reduces conflict points — areas where drivers could potentially crash. The Federal Highway Administration reports DDI’s reduce these conflict points by nearly half. That’s why TxDOT has plans to add more to busy intersections. However, people have mixed feelings.
With one driver saying he still doesn’t “know what to do so yeah, definitely avoid it if I can.” And another seeing the benefit saying, “I like it because it keeps the traffic moving, so that’s a plus.”
Next year, Williamson County drivers can expect to see a DDI open up in their area at I-35 and Williams Drive in Georgetown. TxDOT also has plans for DDIs along Loop 360 with one at RM 2222 and potentially another at Bee Cave Road as well as one at I-35 and Wells Branch Parkway.