By what percentage will weekday vehicle entries into the charging zone fall during the first full year of operation, compared with the year before?

Final estimates for the weekday vehicle entry reductions in the first full year are: 0% for no charge, 12.5% for $9 all-day, 17.8% for $15 all-day, and 7.0% for $9 peak-only.\n\nInitial logic and parameters are validated against the New York $9 Congestion Relief Zone, which achieved an 11% reduction 2 sources, alongside historical international cordons like London and Stockholm 2 sources. Standard processing applied to baseline traffic recovery confirms that without a price signal, entry volumes will remain effectively flat, balanced by worsening regional congestion inrix.com and recovering downtown transit nita.illinois.gov.\n\n**$9 All-Day:** Implementing a $9 fee per entry between 6am and 8pm drives a 12.5% reduction. This leap past the New York benchmark is driven by structural mechanisms: the fee is strictly per-entry rather than daily-capped, heavily suppressing repeat commercial and ridehail trips. Additionally, the small cordon size and robust transit alternatives, with all eleven Metra lines terminating downtown nita.illinois.gov, accelerate mode shift.\n\n**$15 All-Day:** Escalating the charge to $15 yields a 17.8% reduction. This demonstrates sharply diminishing returns due to sub-proportional elasticity, as the most price-sensitive trips are eliminated at the $9 threshold. A premium tier sets in motion aggressive secondary adaptations, primarily an increase in park-and-walk behavior outside the cordon boundaries and intense political friction resulting in broader carve-outs nber.org.\n\n**$9 Peak-Only:** Charging $9 exclusively during peak hours yields a highly diluted 7.0% total weekday reduction. The defining mechanism here is trip retiming rather than trip suppression. Evidenced by New York's hourly data 2 sources, drivers exploit unpriced shoulder and midday windows, creating massive entry bunching immediately adjacent to the toll hours. Peak congestion falls, but the all-day metric simply absorbs the displaced traffic.