The Zcuintlis aka the "Yellow Dogs". Autonomous racing vehicles modified to watch the city limits and the military facilities boundaries. They were also modified to carry a human pilot, but their free will caused many accidents. The machines still do their job by their selves. Workers only ride them for maintenance purposes.
This is actually an old model, it was modeled in carrara 5 a couple of years ago. This was re-modeled in Maya and textured&post in Photoshop.