The three dominant themes early in the Commuting in America series were the auto boom in commuting, the boom in workers, and the boom in suburbanization. As we have seen in previous briefs, the worker boom has passed, with subsequent decades forecast to have markedly slower growth in the workforce (Brief 3 and  Brief 4). Suburbanization, while pronounced dead by critics and arguably weakened by higher energy costs and the economic recession, remains strong, based on Census data (Brief 4). The auto boom appears to have completed its rapid growth cycle and has stabilized at very high levels, remaining the dominant mode with only modest signs of retrenchment. The notably different trend is in the continuing slide of carpooling since the start of statistical observation. This brief presents data describing private vehicle use trends and relationships.