Chapter 03 · Other Findings

Traffic, Transit, and the Spillover Effects That Did — and Didn't — Appear.

The air-quality analysis is the clearest finding in this project, but it is not the only pattern examined.

The analysis also tested whether fewer vehicles entered Manhattan, whether transit ridership increased, and whether congestion-zone avoidance produced spillover taxi demand near the cordon boundary.

The evidence suggests vehicle entries declined modestly, transit ridership increased unevenly across modes, and the anticipated taxi spillover pattern did not appear in yellow-taxi data.

Vehicle entries into Manhattan

Bridges and Tunnels Declined, Modestly.

Bridge and tunnel volume declined during the real comparison window and rose slightly during the placebo year. The chart shows pre vs. post within each window; the difference between them is the zone-attributable effect.

MTA bridge and tunnel volume: real comparison vs. placebo Real-window pre vs. post (left pair) declined 1.3%; placebo-window (right pair) rose 0.4%. The difference-in-differences is approximately −1.75 percentage points. 0.86M 0.88M 0.90M 0.92M 0.94M 0.96M 0.93M Pre 0.92M Post Real comparison · −1.30% 0.92M Pre 0.93M Post Placebo (no policy) · +0.45% Vehicles per day
DiD −1.75 pp Real change − placebo change

The confidence interval narrowly excludes zero — a detectable but modest reduction in vehicle entries beyond ordinary fluctuation. After April 2025, MTA reporting shifted from plaza-level counts to aggregate systemwide totals, which limits per-crossing analysis.

Transit ridership

Buses Gained the Most, but the Signal Is Mixed.

Buses gained the most ridership; subways gained too. The commuter-rail modes (LIRR, Metro-North, Staten Island Railway) drifted slightly negative — but those negatives appear in the placebo year too, suggesting recovery saturation rather than a congestion-zone effect.

−20.0 −10.0 +0.0 +10.0 +20.0 Bus +10.0 Subway +3.9 LIRR −6.1 Metro-North −6.6 Staten Is. Rwy −7.1 DiD vs. placebo (percentage points)

Important caveat: the bus result overlaps with major MTA service expansions during the study period — the Queens bus network redesign and 16 enhanced routes citywide — so it reflects a combination of mode shift and improved service availability. The analysis cannot isolate how much of the increase was driven directly by the toll.

Testing for spillover

The Expected Substitution Patterns Did Not Appear.

One concern surrounding congestion pricing was that commuters would avoid the toll by switching to transit near the cordon edge, then completing trips into Manhattan using taxis. If that behavior occurred at large scale, yellow-taxi pickups should increase disproportionately near congestion-zone boundaries, around major transit hubs, during commute periods, and along hub-to-zone corridors. The analysis tested each of those predictions.

Instead, yellow-taxi pickups increased relatively uniformly across distance bands from the congestion zone, with no strong spatial gradient near the boundary itself. None of the expected spillover signatures appeared consistently in the yellow-taxi data.

This does not rule out spillover entirely. High-resolution FHV trip records for Uber and Lyft were unavailable at the spatial scale required for equivalent analysis.

+0.0 +50.0 +100.0 +150.0 0–1 mi +6.7 1–3 mi +13.1 3–5 mi +92.9 5+ mi +117.3 Inside cordon +6.4 Yellow-taxi pickup change vs. placebo (percentage points)

Yellow-taxi pickups by distance from the congestion zone. The modal-substitution-at-the-edge hypothesis predicts a sharp peak near the boundary; the data does not show one.

Why the project changed

Three Findings Became Smaller; One Held Up.

An earlier version of this project treated traffic, transit, taxis, and air quality as findings of roughly equal weight. After introducing placebo comparisons and extending the time window, several of those effects became smaller, more conditional, or statistically ambiguous.

The air-quality signal remained the most spatially coherent and methodologically robust result, so the project was reorganized around that finding. The transportation analyses remain important context, but the evidence supporting them is weaker and more mixed.

Continue · Chapter 04 Verdict What the evidence suggests, what remains uncertain, and where the analysis reaches its limits.