Liz,
These ladies disappeared from 1717 E. Delmar Street which is northeast and just over 2 miles from the location of the Hulston Cancer Center at 3850 S. National Ave as the crow flies. Driving from Delmar to the location of the referenced area would be more like 3 miles. The area around Delmar Street is primarily residential. The area around the Hulston Cancer Center (S. National at 360 - the James River Freeway) back in 1992 was an area containing hospitals (Cox South and Doctor's Hospital) and several other office type buildings occupied by various doctors (Smith Glenn Calloway etc.). If you go to Map Quest and enter either of these address you will be able to see the distances quite easily.
Of interest is that the freeway was complete to Kansas Expressway in 1992, no additional extension of this freeway was undertaken until 2002 - so there is no chance the bodies would be under the freeway. Also of note is according to Greene County Assessment records, 120,000 square feet of asphalt paving was placed on the Cox property (Hulston Cancer Center) in 1990. Link:
http://www.greenecountyassessor.org/Datalets.asp?gsp=Oby_nh&mnu=PSearch&submnu=OutBuildings&pin=1907209006&cp=1&tp=1&Data1=
Having lived in this area for most of my adult life and knowing when things were built, I have serious doubts that these three ladies are buried under any asphalt paving or any freeway systems around town.
There has been no recent reporting on this case for some time now, however I can tell you that everytime bones are found anywhere in the area, they do run DNA tests to check. I can tell you that the area around Springfield is very rural with lots of hills and valleys, lots of heavily wooded areas, rivers and creek beds with steep bluffs, as well as state forests.
If I hear of anything I will post it for you here. Believe me it is still a topic of discussion in this neck of the woods.