This page details the Motor Parkway in Bethpage State Park. During explorations in 2006, 2009, 2014 and 2015 I found a total of 3, possibly 5 posts and remnants of the Parkway itself. Other websites, most prominently vanderbiltcupraces.com, have described the recent uncovering and resurfacing of the parkway in the park since 2012 with the hope that markers would be erected noting the parkway's significance. However, as of 2015 no makers have been erected!
The picture below shows the approximate locations of three Motor Parkway posts in the park. Another 2 posts I found are shown in the 2006 section below, but unfortunately when I took the picture I did not jot down their location. These might be the same posts shown in the more recent photos but I don't think so. I've labeled the posts of known location A, B, and C.