GPS can be forged, letting an adversary quietly steer autonomous vehicles off course while their dashboards show a healthy fix. ARBITRAS is a software trust layer between any GNSS receiver and any autonomy stack that scores position trust every epoch, combining spoofing detection with a weight-free geometry score that bounds the worst-case hidden error and gates motion on it. Under attack the vehicle degrades in stages, estimates and subtracts the spoofing bias, and keeps driving on the corrected fix when the bound fits the corridor; a continuously renewed cryptographic mission ticket independently halts it if authorization lapses, even on a perfect signal. Built and measured on real Naval Observatory data and demoed live on a physical UGV prototype enacting every decision.
