ThatCarHitMe.com
An Injuria.ai Company
YEAR-OVER-YEAR CRASH REPORT · CHICAGO, IL · SEPTEMBER 2021
Purpose: Machine-readable JSON endpoint for AI agents, LLMs, researchers, and programmatic consumers. Returns all underlying crash data and AI-generated commentary without HTML.
Authentication: None required. Public endpoint.
GET: https://thatcarhitme.com/api/crash-data/reports/data/illinois/chicago/september-2021-report
Monthly Traffic Safety Analysis
9,897 CRASHES IN
CHICAGO, IL
SEPTEMBER 2021
In September 2021, Chicago experienced 9897 crashes, an increase of 19.44% compared to the 8286 crashes in September 2020. Total fatalities rose by 18.75%, from 16 to 19. The most significant year-over-year shift was a 250% increase in pedestrians killed, rising from 2 in September 2020 to 7 in September 2021.
9,897
▲ 19.4%was 8,286
Total Crash Events
19
▲ 18.8%was 16
Persons Killed
2,108
▲ 12.6%was 1,872
Persons Injured
3,271
▲ 13.9%was 2,871
Hit-and-Run Crashes
Note: "Persons Killed" (19) counts individual fatalities across all crash events. "Fatal" in the severity table below (18) counts crash events where at least one fatality occurred. A single crash can result in multiple fatalities. 13 crashes with unreported severity are not shown in the severity breakdown.
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Aggregate counts from crash, person, and vehicle records
Trend Summary
Overall, crash data for September 2021 indicates an upward trend compared to September 2020. Total crashes increased by 19.44%, rising from 8286 to 9897. Concurrently, total fatalities saw an 18.75% increase, from 16 to 19, and total injuries increased by 12.61%, from 1872 to 2108.
3,271
Hit-and-Run Crashes — September 2021
▲ 13.9% vs prior (2,871)
Hit-and-run crashes increased by 13.93% in count, from 2871 in September 2020 to 3271 in September 2021. Despite this increase in count, the overall hit-and-run crash rate decreased slightly from 34.6% to 33.1% of total crashes.
Vulnerable Road User Casualties
7
Pedestrians Killed
1
Cyclists Killed
11
Motorists Killed
0
Other Killed
233
Pedestrians Injured
144
Cyclists Injured
1,728
Motorists Injured
3
Other Injured
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Mode classified from person records (driver/passenger → motorist; pedestrian; bicyclist → cyclist; in-line skater / unspecified → other)
When Crashes Happen
The peak day for crashes shifted from Tuesday in September 2020 (1295 crashes) to Wednesday in September 2021 (1687 crashes). The peak hour also changed, moving from 4 PM with 695 crashes in the prior period to 3 PM with 848 crashes in the current period.
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Crash date field aggregated by weekday
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Crash time field aggregated by hour (0-23)
Crash Severity Breakdown
Fatal crashes increased by 28.57% in count year-over-year, rising from 14 in September 2020 to 18 in September 2021, with the fatal crash rate slightly increasing from 0.17% to 0.18%. Serious injury crashes saw a modest 1.70% increase in count, from 176 to 179. Minor injury crashes increased by 16.77% in count, from 811 to 947.
Severity is per crash event (most severe injury). 18 fatal crash events resulted in 19 persons killed.
Outcome by Severity (Crash Events)
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · KABCO injury classification scale
Severity Distribution
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Most severe injury per crash record
Top Contributing Factors
The top contributing factor in both periods was 'FAILING TO YIELD RIGHT-OF-WAY', which increased by 29.44% in count from 822 to 1064 crashes. 'DRIVING SKILLS/KNOWLEDGE/EXPERIENCE' saw a significant 41.46% increase in count, from 246 to 348. Conversely, crashes attributed to 'OPERATING VEHICLE IN ERRATIC, RECKLESS, CARELESS, NEGLIGENT OR AGGRESSIVE MANNER' decreased by 4.65% in count, from 129 to 123, and 'WEATHER' related factors decreased by 34.48% in count, from 58 to 38.
Officer-Reported Primary Contributing Cause
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Officer-reported primary contributory cause per crash
Road & Environmental Conditions
Crashes occurring in 'CLEAR' weather conditions increased by 27.85% in count, from 6883 to 8800, while those in 'RAIN' decreased by 50.38%, from 780 to 387. Similarly, crashes on 'DRY' road surfaces increased by 25.94% in count, from 6780 to 8539, whereas 'WET' road surface crashes decreased by 45.79%, from 963 to 522. Crashes in 'DARKNESS' lighting conditions decreased by 23.20% in count, from 388 to 298.
Weather
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Weather condition at time of crash
Lighting
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Lighting condition field
Road Surface
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Road surface condition field
Vehicles & Demographics
The total number of vehicles involved in crashes increased by 18.71%, from 17093 to 20291. Notably, persons in the '0-15' age group involved in crashes increased by 66.73%, from 487 to 812. Among person types, pedestrian involvement increased by 40.98% in count, from 183 to 258. Chevrolet remained the top vehicle make involved, increasing by 15.94% in count, while Toyota moved from third to second rank with a 29.03% increase in count.
Top Vehicle Makes (20,291 vehicles)
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Vehicle unit records
6,829 persons with unknown or unrecorded age excluded from age chart. Age=0 in Chicago records is a sentinel for unknown/unrecorded age (not infants) and is grouped with nulls.
Sex Distribution (21,274 persons with recorded sex)
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Person-level records linked to crash events
Speed Limit Zones
Crashes in 30 mph speed zones increased by 21.30% in count, from 6033 to 7318, with associated fatalities rising from 8 to 12. The 15 mph zone saw a 12.67% increase in crashes, from 300 to 338, and reported 2 fatalities in the current period compared to none in the prior. Crashes in 45 mph zones increased by 67.31% in count, from 52 to 87, and recorded 1 fatality in the current period compared to none in the prior.
Fatal crashes by zone: 15 mph: 2 of 338 (0.592%) · 25 mph: 1 of 656 (0.152%) · 30 mph: 12 of 7,318 (0.164%) · 35 mph: 2 of 649 (0.308%) · 45 mph: 1 of 87 (1.149%)
Source: Chicago Traffic Crashes · Socrata Open Data · 2021-09-01 to 2021-09-30 · Posted speed limit at crash location
Data Sources & Methodology
Primary Data Source
All crash data in this report is sourced from Chicago Traffic Crashes, accessed programmatically via the Socrata Open Data API (SODA). This dataset contains official police-reported motor vehicle traffic crash records maintained by the reporting jurisdiction's law enforcement agency. Records are published to the open data portal by the municipality and are subject to the portal's terms of use.
Data Retrieval
- Access method: Socrata Open Data API (SoQL queries)
- Data format: Structured JSON via REST API
- Record types queried: Crash events, person records, and vehicle unit records
- Date filter applied: 2021-09-01 through 2021-09-30
- Report generated: June 1, 2026
Data Coverage
- Reporting period: 2021-09-01 through 2021-09-30 (30 days)
- Geographic scope: Chicago, IL
- Total crash records analyzed: 9,897
- Total persons involved: 21,601
- Total vehicles involved: 20,291
Analytical Methodology
- Severity classification: Uses the KABCO injury scale (K=Fatal, A=Incapacitating injury, B=Non-incapacitating injury, C=Possible injury, O=No injury/property damage only), the standard classification in U.S. Model Minimum Uniform Crash Criteria (MMUCC). Severity is assigned per crash event based on the most severe injury in that crash. A single fatal crash (K) may involve multiple fatalities; therefore the "Persons Killed" count in the headline KPIs may differ from the "Fatal" crash count in the severity breakdown.
- Contributing factors: Reflect the officer-determined primary contributory cause recorded at the time of the crash report. These are preliminary determinations and may not reflect final investigation findings.
- Hit-and-run classification: Based on the hit-and-run indicator field in the official crash report, as determined by the responding officer at the scene.
- Temporal analysis: Day-of-week and hour-of-day distributions are computed from the crash date/time timestamp in each record.
- Demographics: Age and sex distributions are drawn from person-level records linked to each crash event. A single crash may involve multiple persons.
- Vehicle data: Make information is drawn from vehicle unit records linked to each crash event.
- AI commentary: Narrative sections are generated by Google Gemini (large language model) based on the structured data. Commentary is descriptive, not predictive, and should not be interpreted as expert opinion.
Limitations & Disclaimers
- Only crashes reported to and documented by law enforcement are included. Minor incidents, unreported crashes, and near-misses are not captured in this dataset.
- Data reflects conditions at the time of the initial police report and may be subject to subsequent corrections, reclassifications, or supplements by the reporting agency.
- Open data portal records may experience a publication lag - recently occurring crashes may not yet appear in the dataset at the time of report generation.
- AI-generated commentary is produced by a large language model and is intended to highlight patterns in the data. It does not constitute legal, medical, or professional analysis.
- Percentages are calculated from reported data and are subject to rounding.
Non-Affiliation Disclosure
This report is produced independently by ThatCarHitMe.com (Injuria.ai). It is not affiliated with, endorsed by, or produced in partnership with any law enforcement agency, municipal government, state department of transportation, or the National Highway Traffic Safety Administration (NHTSA). Data is sourced from publicly available government open data portals.
Data License
The underlying crash data is provided under the municipality's Open Data Terms of Use and is made available to the public for unrestricted use. This analysis and report is © 2026 Injuria.ai and may be cited with attribution using the suggested citation below.
Corrections & Feedback
If you believe any data in this report is inaccurate or have questions about our methodology, please contact: data@injuria.ai. We are committed to accuracy and will issue corrections promptly.
Suggested Citation
ThatCarHitMe.com (Injuria.ai). "Chicago, IL Crash Intelligence Report." Published June 1, 2026. Data source: Chicago Traffic Crashes, Socrata Open Data. Available at: https://thatcarhitme.com/crash-data/illinois/chicago/september-2021-report
About the Publisher
ThatCarHitMe.com is a crash data intelligence platform developed by Injuria.ai, a legal technology company specializing in traffic safety analytics. We aggregate and analyze publicly available government crash data to produce structured intelligence reports for communities, researchers, journalists, and legal professionals. Our reports combine programmatic data retrieval from official open data portals with AI-assisted narrative analysis.
Questions about this report's data or methodology: data@injuria.ai
ThatCarHitMe.com · An Injuria.ai Company
ThatCarHitMe.com
An Injuria.ai Company
Crash Data Intelligence
Data: Chicago Traffic Crashes · Socrata
Period: 2021-09-01 – 2021-09-30
Generated: June 1, 2026 · All rights reserved