GM/EMD delivered all SD70MAC locomotives to Burlington Northern/BNSF with the GM HTCR truck. This radial bolsterless truck features three axles, and three traction motors. A truck that has bolsters means that the weight of the locomotive is pressed onto the center of the truck, then spread out through a center plate, and on to coil springs located in between the axles. A bolsterless truck features a kingpin at the center of the truck, and rubber/metallic "packs" that can be seen in the photo above in between the rear and middle axles, and the middle and front axles. The HTCR is also a radial truck, which means that each axle can pivot around the truck frame independently. This reduces wear on the wheels and rails around curves. More information about EMD's radial truck design can be found here: EMD's Radial Trucks.
Information about the HTCR radial truck specifically can be found here:
HTCR radial truck information.