I looked at a lot of Google Map while I was working on the previous post about Briley Parkway. I just wanted to share some additional thoughts that jumped out at me.
There is a pretty significant kink in the main road that looks like it was added in order to avoid the airport runway. This caused the Briley interchange at Interstate 40 to be skewed on an angle making it more difficult to build. Those angles make it difficult to move traffic and keep them at interstate level speeds. I’ve always thought Briley was way too curvy for such a high speed route, and I suspect the leg through Donelson doesn’t meet a lot of the design guidelines about curves on a four lane or higher road. It was much worse before a major overhaul was done around 2008. Looking at the maps (and satellite imagery) makes it pretty obvious why it was so curvy.
When I moved to middle Tennessee in the mid-90’s the of Briley through Donelson and up to Gallatin Pike was extremely curvy and the lanes felt cramped and narrow. It was more than a little dangerous if you drove at the average traffic speed. I wasn’t a middle Tennessean when this part was built, but I suspect it was built in the 1960’s as an alternate to driving through downtown, and/or to get people to Opryland. The curves and cramped feeling were a product of trying to thread a major highway through a dense residential area. The designers obviously tried to veer around the denser populated areas and the cramped feeling was an effort to take up as little space is possible. The version above is actually the rebuilt version which was constructed in the mid-00’s and some of its curves have been smoothed down and adjusted.
That’s just a brief peek into the world of highway layout. There are an impressive number of other factors that also have to be juggled in order to get it just right.