The I-285/I-20 interchanges need a LOT more consideration for partial redesigns. (Tucker: 2015, chapel)

[toll_booth]

Both interchanges have two ramps that are a complete mess at rush hour due to their poor design.

The 285/20 west side interchange has issues stemming directly from design flaws: the 285S-to-20W ramp, and the 20E-to-285N ramp. The former is a sharp turn and only one lane, which forces trucks to slow down, further compounding the already bad traffic that takes that route. The second is even worse--a loop of more than 180 degrees makes even autos have to slow down. That second ramp should be done away with in favor of a flyover ramp, which should be a reasonably gentle curve, not like the sharp, 285E-to-85N flyover at Spaghetti Junction. (Contrast all this with what's going on on the south side of this interchange--much smoother ramps. This is what they should look like.) The first needs to be rebuilt with two lanes and a wider turning radius, which would call for some modest land acquisition. But the only real obstacle around there is a high-voltage power line pylon, as the land just east of there, where the new ramp would go, is undeveloped.

The one on the east side has problem spots as well. Specifically, the 285S-to-20E ramp shoots waaaay too far south, forcing the curve to be far tighter than it needs to be. And there's no excuse for that very tight, 270-degree turn on the 20W-to-285S ramp. Both need to be replaced with flyovers. And there's plenty of undeveloped land just to the northeast, so physically putting them in shouldn't present too much of an obstacle. (Note that the 285N-to-20W ramp is much too tight as well, but that's a rarely-used ramp, so it can go without an upgrade for now.)

[MattCW]

They're currently rebuilding the east side I-285/I-20 interchange which will incorporate collector/distributor lanes to separate out Wesley Chapel Road traffic a bit from merging traffic. Right now, traffic getting off at Wesley Chapel must merge right and traffic from I-285 must merge left so the two traffics collide, sometimes literally which causes more congestion than necessary. I haven't been able to find a final design or lane diagram online, but I'm hoping it will be a [smaller] version of how you have to get off at Chamblee Tucker from I-285.

[testa50]

The interface of the Wesley Chapel interchange and the 285 interchange is madness. Wesley Chapel-bound traffic definitely needs to fly over the 285N-20W traffic.

[toll_booth]

Originally Posted by MattCW

They're currently rebuilding the east side I-285/I-20 interchange which will incorporate collector/distributor lanes to separate out Wesley Chapel Road traffic a bit from merging traffic. Right now, traffic getting off at Wesley Chapel must merge right and traffic from I-285 must merge left so the two traffics collide, sometimes literally which causes more congestion than necessary. I haven't been able to find a final design or lane diagram online, but I'm hoping it will be a [smaller] version of how you have to get off at Chamblee Tucker from I-285.

Though that wasn't the specific problem I was talking about, merging and weaving on 20E from the 285 interchange to Wesley Chapel is indeed a huge problem, and this project will help.

If anyone wants to see what this new collector-distributor project will look like, I found the construction plans here. (Go down to 13-Mainline plan and profile sheets)

[MattCW]

OH GOOD GRIEF! (thanks for finding that, by the way). The CD project isn't going to fix anything except make it harder for I-285 traffic to escape the Wesley Chapel traffic!
WHO DESIGNED THIS IDIOCY!?!?!?

[Airforceguy]

I found this project on GDOT website for July 2015 lettings. The project calls for separating all of the I-285 traffic from I-20 EB traffic before the ramp. GDOT will do this by modifying the lane configuration and putting up lane barriers similar to the ones GDOT recently installed on the I-85 HOT lanes. While this project will be beneficial, I feel it is nothing more than a band aid on a bullet wound. That whole interchange needs to be redone.
Here are some renderings of the project:
i-20i-285interchange3 by brandon walker, on Flickr

i-20i-285interchange2 by brandon walker, on Flickr

i-20i-285interchange1 by brandon walker, on Flickr

Link to project:Project Search

[JMatl]

I agree. The left lane exits are dangerous, and need to go. The same thing applies to the Eastside interchange of these Interstates.

[cwkimbro]

I agree this isn't a major restructure and it is a relatively cheap thing to do, but after looking at it for awhile I see it as more than a band aid.

This could actually be a really good thing for Douglas County and some South Cobb commuters.

The justification is simple. Civil engineering has actually improved over the years and they monitor traffic flows and merging much more carefully.

This change will open up capacity going on the two most heavily traveled directions.

First an explanation of existing conditions. Most traffic in this direction, particularly in the morning, more heavily flows North and East. In other words towards Cumberland/Perimeter and towards Downtown.

I-285 gets fairly backed up from all the north bound traffic, whereas I-285 southbound flows relatively freely.

Approaching the interchange are 4 lanes. The southbound traffic has their own dedicated lane and cars going southbound can also exit from the right center lane.

This means out of 4 lanes the two heaviest traveled traffic flows share 3 lanes and the southbound traffic can still take up space in one of those lanes. Out of those 3 lanes the right most lane is shared for northbound and east bound traffic. In effect the east bound traffic is constrained to the left two lanes in the morning rush hour.

With the re-striping they are actually adding a lane on the bridge. East bound traffic will have 3 dedicated lanes. Northbound traffic can now make use of the 4th lane that was lightly used by Southbound traffic before. The northbound traffic is better off, because they are sharing a lane with southbound traffic instead of the heavily traveled eastbound route.

Now the only bad caveat is the north and southbound traffic must share a single lane of the 4 approaching the interchange. In the future a minor widening for half a mile to a mile approaching the interchange might be needed as the total amount of traffic going north and south increases. This could prevent all I-285 bound traffic from passing through a single lane. Still, that is a cheaper upgrade than anything touching a bridge.

Traffic going into town will notice a big difference from this.

[Craziaskowboi]

Nothing is an improvement until the left-lane ramps are eliminated, especially since there's enough room in the right of way to build flyover ramps.

[alco89]

I drive through this everyday. This WILL be an improvement. Every morning there is a line backed up waiting to get onto I-285 N, so what do people decide to do? Instead of waiting their turn they wait til the last second to dart over into 3rd lane that sends you down the ramp to 285, which requires them to slam on their brakes, which then slows down traffic in the middle lane. Because of that, people start getting over into the fast lane to avoid braking, causing the people already there to panic and brake. Before you know it, ALL the lanes heading into the city are crawling through that interchange just because people are selfish and wanna skip the lines. Separating the 285 traffic by barriers ahead of time will force people get in their lane and stay there and decrease congestion in the travel lanes heading into the city.

Of course they could do more. I'd like to see them create collector distributor lanes in both directions on I-20 between Fulton Ind and 285 to cut down on all the weaving (similar to what they did for 20, 285, and Wesley Chapel). They also need to replace that hairpin turn for I-20 E to I-285 N with a flyover so the TONS of trucks don't have to go 5 mph to execute it.