For eight years Chicago ran a public speedometer on its own surface streets. The Traffic Tracker — whose archive the portal now marks “This dataset is no longer updated” — logged an estimated speed for each of 29 arterial regions every few minutes, 10,776,684 region-interval rows from March 9, 2018 to April 30, 2026. The estimates come from an elegant trick the city’s own documentation describes: the tracker “estimates traffic congestion on Chicago’s arterial streets (non-freeway streets) in real-time by continuously monitoring and analyzing GPS traces received from Chicago Transit Authority (CTA) buses” — the buses are the probes. Read whole, the archive says: the fastest hour on Chicago’s arterials is 3 a.m. (a 30.85 mph average estimate in 2025) and the slowest are the 4 and 5 p.m. hours, tied at 23.33; the slowest region is the Chicago Loop (19.38) and the fastest is Riverdale-Hegewisch (33.41); and the single most congested cell in the 2025 table is the Loop at 5 p.m., where the average estimate is 13.9 miles per hour. Every figure on this page is an average of the tracker’s estimates — not a measurement of any driver’s speed.
Chicago Traffic Tracker – Historical Congestion Estimates by Region (kf7e-cur8), 10,776,684 region-interval rows, March 9, 2018 – April 30, 2026, 29 regions · retrieved August 27, 2026; the portal marks the file no longer updated · averages exclude the 896,315 rows carrying a zero estimate, which are counted separately belowA speedometer made of buses
The Chicago Transit Authority is a separate agency, but its buses doubled as the city’s traffic sensors: per the portal, the tracker estimated congestion by analyzing the GPS traces the buses sent. That mechanism shapes what the file can see. 8.3 percent of all rows carry a zero estimate, and they concentrate overnight: in 2025, 56.9 percent of 2 a.m. intervals record a zero. The file does not define what a zero means; our reading, labeled as ours, is that the zeros track the hours when few buses are out to serve as probes — and whatever their cause, they are not speeds. This page therefore averages only the rows with a positive estimate and counts the zeros apart, with no other trimming — which also means the file’s highest single estimate, 173.86 mph, stays in the data as filed, one implausible row among ten million absorbed by the averages.
The clock: 3 a.m. is 7.5 mph faster than 4 p.m.
| Hour (2025) | Avg. estimate, mph |
|---|---|
| 3 | 30.85 |
| 5 | 27.23 |
| 7 | 25.06 |
| 8 | 24.84 |
| 10 | 25.47 |
| 12 | 24.89 |
| 14 | 24.34 |
| 16 | 23.33 |
| 17 | 23.33 |
| 19 | 24.70 |
| 21 | 25.48 |
| 23 | 26.47 |
The spread widens where the city is densest. In the Chicago Loop in 2025, the average estimate at 3 a.m. was 27.02 mph; at 5 p.m. it was 13.9 — the arterial grid’s slowest hour-region cell, about three-fifths of the citywide 5 p.m. average of 23.33. Is downtown at rush hour really the slowest place and hour the tracker saw? By this file’s estimates, yes — it is the lowest average estimate in the 2025 table.
The map: a 14 mph spread across 29 regions
| Region (label as printed) | Avg. estimate 2025, mph |
|---|---|
| Chicago Loop | 19.38 |
| Near North | 20.91 |
| Edge Water-Uptown | 21.53 |
| Lincoln Park-Lake View | 22.35 |
| Rogers Park – West Ridge | 23.24 |
| … | … |
| South Deering-East Side | 29.10 |
| Ashburn | 29.70 |
| Beverly-Mt Greenwood-Morgan Park | 30.14 |
| Midway-Garfield Rdg-Clearing | 30.55 |
| Riverdale-Hegewisch | 33.41 |
The pattern is the city’s shape: the slow end of the table is the dense North lakefront and downtown — the Loop, Near North, the region the file labels “Edge Water-Uptown” — and the fast end is the far South and Southwest Sides, led by Riverdale-Hegewisch. The tracker records estimates, not explanations; density, signals, and bus routing all live inside these numbers somewhere, and the file does not say in what shares.
The years: the needle barely moves
| Year | Avg. estimate, mph | Positive-estimate rows |
|---|---|---|
| 2018 (from Mar. 9) | 24.22 | 1,059,964 |
| 2019 | 25.75 | 1,262,090 |
| 2020 | 26.02 | 1,300,135 |
| 2021 | 26.08 | 1,195,392 |
| 2022 | 26.21 | 1,167,736 |
| 2023 | 26.30 | 1,062,080 |
| 2024 | 25.67 | 1,016,598 |
| 2025 | 25.53 | 1,374,810 |
| 2026 (Jan–Apr) | 24.99 | 441,564 |
Across the seven full years the annual average moves inside a band 0.77 mph wide — from 25.53 in 2025 to 26.30 in 2023 — and this page draws no trend from it. The starkest comparison in the file is also its quietest: April 2020’s average estimate, 26.27 mph, runs just 0.62 mph above April 2019’s 25.65. Whatever that month emptied elsewhere, the arterial estimates barely registered it — why, the file does not say, and we leave it open.
- Source: the city’s Chicago Traffic Tracker – Historical Congestion Estimates by Region, 2018–2026 (kf7e-cur8): 10,776,684 rows, one per region per estimation interval, March 9, 2018 through April 30, 2026, for 29 arterial regions; retrieved August 27, 2026. The portal marks the file “no longer updated”; this page reads the archive as it stands. All figures were computed on the portal; no row-level file was downloaded.
- Unit: every figure is an average of the tracker’s region-interval speed estimates, in miles per hour. An estimate is not a measurement of any vehicle’s speed, and no figure here describes an individual driver.
- Mechanism: per the portal’s own description, the tracker “estimates traffic congestion on Chicago’s arterial streets (non-freeway streets) in real-time by continuously monitoring and analyzing GPS traces received from Chicago Transit Authority (CTA) buses.” The Chicago Transit Authority is a separate agency; its buses served as the probes.
- Zeros and oddities: 896,315 rows (8.3 percent) carry a zero estimate and are excluded from every average and counted here instead; they concentrate overnight (56.9 percent of 2 a.m. intervals in 2025) — our reading ties that to the hours when few buses are out, and the file itself does not define a zero. No other filtering or trimming was applied; the file’s maximum single estimate, 173.86 mph, is printed as filed.
- Partial years: 2018 begins March 9 and 2026 ends April 30; both are labeled wherever they appear. No trend is claimed from the annual averages.
Computed by KCM Desk from the city’s Traffic Tracker archive, retrieved August 27, 2026. If you spot an error, corrections come first.
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