A mathematical comparison of string stability transfer functions between sensor-only ACC and wireless-assisted CACC.
Standard Adaptive Cruise Control (ACC) relies on onboard radar to measure distance and relative speed. Because radar filters require several hundred milliseconds to confirm acceleration changes, small deceleration events by a lead car amplify down the line—ultimately causing a phantom traffic jam or a multi-vehicle rear-end collision.
Cooperative Adaptive Cruise Control (CACC) adds a direct V2V wireless link. The instant the lead driver presses the brake pedal, the commanded deceleration value is transmitted to trailing vehicles over sidelink before the lead vehicle has physically begun to slow down. ``` +-----------------------+ PC5 Feedforward +-----------------------+ | Lead Vehicle | --------------------------------> | Trailing Vehicle | | Brake Pressed (t = 0) | Decel Intent: -3.2 m/s^2 | Calipers Precharged | +-----------------------+ Latency < 8ms +-----------------------+ | v Synchronous Deceleration Zero Phantom Amplification ```
Platoons running V2XControl demonstrated string stability factors strictly below 1.0 across all disturbance frequencies, successfully operating with headways as tight as 0.6 seconds at 120 km/h.