This is a 64-bit running total of the bytes that the Committed Access Rate (CAR) policy on this interface has allowed through, i.e., traffic that complied with its configured rate limit. Because CAR rate-limits traffic per interface/policy, this counter lets an admin see actual throughput passing a specific CAR-limited link without wrapping every few seconds the way the 32-bit ccarStatSwitchedBytes would on a fast interface. For example, on a 1 Gbps uplink capped at 500 Mbps CIR, this counter might read into the trillions of bytes after an hour of near-saturated legitimate traffic, a value the 32-bit counter would have already rolled over many times.