A level 4 autonomous vehicle suddenly loses GPS signal in an urban canyon (tall buildings block satellite coverage). The localization module was fusing GPS, IMU, and wheel odometry. What should happen?
AThe vehicle should immediately stop, because GPS is required for safe navigation
BThe vehicle should continue using IMU and wheel odometry, but accumulate drift over time; if drift exceeds a safety threshold, it should request human takeover or safe stop
CThe vehicle should request that the human driver resume control immediately, regardless of traffic conditions
DThe vehicle should switch to dead reckoning until GPS returns, with no effect on localization confidence
This modular architecture is the industry standard for autonomous vehicles (used by Waymo, Tesla, Cruise, Uber ATG) because it balances theoretical optimality (joint optimization would be ideal) against practical constraints (testability, modularity, real-time performance). It is the engineering choice that makes safety engineering feasible.