Man-portable tools for noninvasive evaluation of ballast condition are being developed to assist with walking inspection of railways. A prototype instrument called the Radar Ballast Inspection Tool (RABIT) has been built that combines ground-penetration radar and real-time analysis algorithms with the goal of nondestructively assessing ballast condition and providing immediate results in the field. The first generation RABIT was designed to take measurements from single locations on the track with the goal of providing real-time ballast condition measurements to inspectors in the field. In order to train the analysis algorithms and test the system performance, a series of full-scale track models was constructed indoors that had varying amounts of ballast fouling and moisture. RABIT measurements were taken at various stationary locations on each track model. These measurements had a high degree of repeatability and provided reliable ballast fouling and moisture content when these values were below about 15 % and 2 % by weight, respectively. However, when the fouling or moisture content (or both) increased beyond these levels, the readings varied from location to location, indicating spatial variability in ballast condition. Despite efforts to build a uniform ballast model, adding moisture by irrigation caused the fine-grained material to migrate downward, resulting in heterogeneous conditions. Field conditions will almost certainly have more variability than controlled laboratory conditions. Therefore, it was concluded that rather than taking measurements at single locations, the measurements need to be made continuously over a few cribs. Accordingly, a second-generation RABIT has been built that is more lightweight and can roll down the track to make measurements over a more representative length of track. A comprehensive field test program to test and verify the new instrument is in progress.