Determining the "busiest" freeway depends on whether you measure by sheer vehicle volume or congestion delay. In 2026, the Highway 401 in Ontario, Canada, specifically the stretch through Toronto, continues to hold the title for the highest annual average daily traffic (AADT), with over 500,000 vehicles passing through its widest 22-lane sections daily. However, when measuring "time lost," cities like Mexico City and Istanbul frequently top global congestion indices. In the United States, the I-405 (San Diego Freeway) in Los Angeles remains the most congested corridor, where commuters lose an average of over 80 hours per year to gridlock. This "freeway fatigue" is a major driver for the 2026 expansion of automated traffic management systems aimed at reducing the environmental and economic impact of these massive vehicle bottlenecks.