OKC HazMat Route I-40, WB, but not EB?

There is a HazMat route restriction on I-40 through Oklahoma City, OK. Going westbound there is a large highway sign indicating HazMat must bypass downtown using I-240w (which turns into I-44E) before rejoining I-40 westbound. My RM 740 GPS shows the same route.

The interesting bit is going eastbound approaching OKC. There are no highway signs showing the HazMat route restriction. My GPS shows the route to be right through downtown OKC on I-40.

The National HazMat Route Registry shows the restriction applies going east or west through OKC.
Why are there no signs for HM/HC to bypass when going eastbound? This is the only HazMat restriction (so far) that my GPS hasn't warned me about. It usually warns me about false restrictions that don't really exist.