  Various control strategies and field experiments have been designed for
connected and automated vehicles (CAVs) to stabilize mixed traffic that
contains both CAVs and Human-driven Vehicles (HVs). The effect of these
stabilizing CAV control strategies on traffic safety is still under
investigation. In an effort to prioritize safety over stability, a
safety-critical filter via control barrier functions (CBFs) can be designed by
modifying the stabilizing nominal control input in a minimal fashion and
imparting collision-free driving behaviors for CAVs and HVs. However, such
formal safety guarantees can be violated if there are delays in the actuation
and communication channels of the CAV. Considering both actuator and sensor
delays, and disturbances, we propose robust safety-critical traffic control
(RSTC) design to ensure ``robust safety'' of the mixed traffic. While
predictor-based CBF has been developed to compensate for the actuator delay,
uncertain speed disturbances from the head vehicle cause prediction error and
require novel robust CBF design. Besides, safety-critical control with sensor
delay also remains an open question. In RSTC, a state predictor with bounded
error is designed, and robust CBF constraints are constructed to guarantee
safety under actuator delay and disturbances. When there is a sensor delay, a
state observer is designed and integrated with a predictor-based CBF to ensure
robust safety. Numerical simulations demonstrate that the proposed RSTC avoids
rear-end collisions for two unsafe traffic scenarios in the presence of
actuator, sensor delays and disturbances.
