Photo courtesy of Alabama Department of Transportation.
Workers are building the new diverging diamond interchange at the intersection of Interstate 65 and Lakeshore Parkway in Homewood.
Gary Smith remembers driving through a diverging diamond interchange about a dozen years ago in Atlanta.
And the Alabama Department of Transportation opened Alabama’s first diverging diamond interchange along Interstate 10 in Baldwin County in 2020. But the concept isn’t new.
Diverging diamond interchanges have been around probably at least 20 years, said Smith, ALDOT’s operations engineer for the East Central region, which includes Birmingham and Homewood.
Which yields the question: What took Alabama and Homewood so long to get on board with the idea?
Photo courtesy of Alabama Department of Transportation.
The new design for the I-65 interchange at Lakeshore Parkway begins to take shape. As construction continues, motorists should start to see lanes of traffic shift to new routes early this fall, according to ALDOT.
The latest diverging diamond interchange is under construction in Homewood at the crossing of Interstate 65 and Lakeshore Parkway, also known as Alabama 149. According to ALDOT, more than 50,000 vehicles travel through those on-ramps and off-ramps every day.
“There’s always a resistance to change,” Smith said. “I still get calls frequently about roundabouts and DDIs saying, why are we doing this? This will not work. People are just real hesitant to change. It’s a lot of money to spend on something that you’re not positive is going to work.”
But the state has watched other areas that implemented them with success, he said. “We’ve seen now they do have a positive benefit,” Smith said. “It just took a little while for us to enact some, I guess, and fund them in Alabama. But once we have, we have realized they’re beneficial.”
The state initially sought construction bids for the Lakeshore DDI in 2021, but ALDOT rejected all the bids it received. Smith said the plan was changed somewhat to make it more cost-effective.
“It just took a while to get funding in place, I guess, to let it the second time,” he said. “We let it in 2025. There’s basically a four-year delay from the first letting to the second.”
The total cost of the project is about $29 million. The city of Homewood’s share is about $5.8 million, with Jefferson County contributing $1 million toward the city’s required local match, Homewood City Engineer Amy Zari said.
The impact in Homewood should be obvious.
This map shows how the new I-65 diverging diamond interchange at Lakeshore Parkway will work once it is completed and opens, allowing for fewer traffic lights and more continuously flowing traffic. Map courtesy of Alabama Department of Transportation.
“The diverging diamond interchange is expected to significantly improve traffic flow, reduce congestion and enhance safety at the interchange,” Zari said. “This design allows vehicles to make left turns onto the I-65 ramp without crossing opposing traffic, improving operations during peak travel periods. In addition, the DDI configurations require fewer [traffic] signal phases, which helps reduce vehicular delays and promotes a more efficient flow of traffic.”
No one would ever confuse a diverging diamond interchange with a roundabout, which manages surface-level traffic without a traffic signal with a series of right turns. Conversely, a diverging diamond is particularly effective where there had previously been a lot of left turns at an off-ramp.
“At this [Lakeshore] interchange, we do have a lot of left turns, both getting on and off the interstate,” said Smith, the ALDOT engineer.
With the diverging diamond design, “Left turns flow freely coming off the interstate because you don’t have to cross traffic there. The traffic crosses on the correct side of the interchange with the ramp. You do not have to have a signal there to get you across; you can flow freely to the left.
“People coming southbound on [I-]65, say, will not have to go through a traffic signal to go left, to go out Lakeshore and vice versa,” he said. “If you’re coming northbound and you want to get over to the shopping area, you will flow freely from the ramp onto Lakeshore toward the shopping area. It really provides smoother, quicker intersection movement there, instead of having a signal there at the ramp.”
Despite being a new way of entering and exiting I-65, Smith said he doesn’t think motorists will require special instructions to maneuver the DDI.
There will be signs, and the roads will be striped, he said. “The first couple I went through, I didn’t know what I’d done,” he said. “I just followed the stripes. You go through it, [and] you don’t have a problem with it. … It’s pretty intuitive.”
The diverging diamond interchange will feature two traffic signals, one on either end of the bridge crossing I-65.
“You do flip sides,” Smith said. “Your [eastbound] and westbound traffic ... on Lakeshore swaps sides. Where they swap, there will be traffic signals. You’ll still have two signals. If you’re trying to go end to end down Lakeshore, which may be green and may be red, you may have to stop. You may not, but people coming off the interstate won’t have to stop. As they come off the interstate, they’ll be able to get on [Lakeshore]. That’s the benefit of it.”
The ALDOT engineer said motorists exiting the interstate can flow freely to the left or the right whenever they come off the ramps.
“Either direction coming up the interstate ramps, you move without having to wait for a signal, which will be neat,” he said.
Smith recalled some driver confusion when roundabouts were added to roadways. The frequent question then was: Who has the right of way? The answer, he said, is the person in the circle has the right of way, and the person approaching the circle has to yield.
“People have figured it out quite quickly,” he said. “There’s no question anymore who has right of way. Sometimes when you were in the circle when it first opened up, you had to be ready to slam on your brakes because the person approaching may not stop. But I never see that anymore. They yield the right of way to the person already in the circle. Once you figure that out, [roundabouts] work really well.”
So people exiting the interstate onto Lakeshore Parkway will have right of way?
Photo courtesy of Alabama Department of Transportation.
Workers put down pavement for the new ramp to I-65 at Lakeshore Parkway in Homewood.
“Well, they just don’t have to stop due to the nature of the roadway,” Smith said. “In a sense, they have right of way. Whenever they get to the far end of the bridge, to where they cross back onto their correct side of traffic, they may have to stop. But that’s only one signal. They’ll have to stop once possibly instead of twice. Now, you have one [stop] at the top of the ramp, and you have one at the other side of the bridge, at the other ramp. You will only have to stop once at the most, instead of now at two at the most.”
After a four-year delay from when construction bids were initially sought for the project, completion of Homewood’s DDI is within sight. Smith said completion can be gauged two ways.
“The main way that will be apparent to the traveling public is when traffic shifts and new traffic patterns are in place,” the ALDOT engineer said. “That will be, I would say, early fall at the rate they’re going now. They’ve made some pretty good progress lately. But early fall is when the [motorists] will notice the new traffic pattern of being shifted and crossing directions … actually going through a diverging diamond interchange.”
Smith said the project itself will probably not be truly complete until next spring when the final layer of asphalt, the permanent traffic signals and any additional concrete work have been done after the traffic shift is made.
“All those kind of things will be taken care of over the winter and into the early spring,” he said. “It may be April or so before things are totally complete there. But as far as the traveling public and the traffic know, the big change will be implemented and operational changes will be implemented, I’d say, early fall, maybe September.”
