That is going to be some kind of undertaking. I imagine it’s going to be some form of cut and cover construction (as opposed to tunnel boring) which means that the parking lot in the middle will potentially be out of commission for some time. The real trick is the track shuffle that happens when building under an active rail line. Somehow, I see tunnel-jacking (like the Big Dig in Boston under the South Station tracks was achieved) as an expensive way of accomplishing this feat

I also wonder how the northbound traffic will exit and if there will be some kind of re-alignment of East Durham Street. It will be interesting to see how this plays out.

My other thought is that the tunnel will only go under the tracks with the realignment of Cary Street to the west through the parking lot in the diagram. From the map, there might be a funky interchange with East Durham and Chapel Hills instead of a tunnel portal. Or the alignment might take a jog to the east to Bowden Street. Either way, it’s going to make a mess out of one of Cary’s municipal parking lots unless they also intend to put another parking deck in the complex.