Slow Them Down
Open Source
Slow Them Down helps you estimate vehicle speeds on your residential street using just your phone’s camera. Record a short video of passing traffic, mark two frames, and get an instant speed estimate — no radar gun needed.
Designed for neighbors and community advocates who want data to support traffic calming efforts, Slow Them Down calculates the V85 speed (the speed at or below which 85% of vehicles travel), the standard metric
used by traffic engineers to evaluate street safety.
This app is open source under the MIT license and the source code is available here.
Android beta — join the closed test
How It Works
- Record — Point your phone at passing traffic and capture a short video
- Mark — Select two frames and tap where the vehicle appears in each
- Measure — Get an instant speed estimate calibrated to real-world distances
- Report — Share data with the people who can make your street safer
Features
Speed Estimation
Estimate vehicle speeds from video using frame-by-frame analysis. Calibrate with a known vehicle length or a measured distance on the street.
Visual Reports
Speed distribution histograms, hourly trend charts, and speeds-over-time scatter plots. Filter by street to isolate problem areas. See V85, mean, median, and over-limit percentages at a glance.
Report to Your City
Send speed data directly to your local traffic department with one tap. The app matches your location to a built-in directory of city, county, and state agencies, then composes an email with V85 stats and an attached PDF report.
Privacy-First Design
All video processing happens on-device. Faces and license plates are automatically detected and blurred before you share anything. No accounts, no cloud uploads, no
tracking.
Export & Share
Export as CSV for spreadsheets or PDF for presentations. Filter by street before exporting. Share via email, AirDrop, or any app on your phone.
Community-Powered Agency Directory
The agency directory grows with contributions from users like you. Don’t see your city? Open a PR on GitHub to add it.
Logging & Tracking
Every speed measurement is logged with timestamp, street name, vehicle type, direction, and calibration method. Cross-street detection automatically tags entries with the
nearest intersection.
Privacy Policy
Effective Date: March 6, 2026
Data Storage
All video processing and speed calculations occur locally on your device. There is no backend infrastructure, no user accounts, and no behavioral analytics.
Camera Access
Videos are processed entirely on-device and never uploaded. Faces and license plates captured in video frames are automatically detected and blurred on-device before any sharing or export. This processing uses Apple Vision (iOS) and ML Kit (Android) and does not transmit any data.
High fidelity location data, if requested, is used only during active sessions and is not persistently stored or transmitted.
Local Storage
Speed logs and calibration settings remain on your device using native storage systems (SwiftData for iOS, Room for Android). Deleting the app removes all locally stored data.
Crash Reporting
The app uses Firebase Crashlytics to automatically detect and report application crashes. When a crash occurs, Crashlytics collects technical diagnostic information including device model, operating system version, app state, and stack traces. This data is sent to Google’s Firebase servers and is used solely to identify and fix stability issues. Crashlytics does not collect your speed measurements, videos, location data, or any other personal content.
Third-Party Services
| Service | Purpose | Data Collected | Privacy Policy |
|---|---|---|---|
| Firebase Crashlytics | Crash reporting | Device model, OS version, app state, crash stack traces | Firebase Privacy Policy |
Children’s Privacy
Slow Them Down is not directed at children under 13 and does not knowingly collect personal information from children.
Changes to This Policy
Updates to this privacy policy will be reflected on this page with a revised effective date.
Terms of Service
Effective Date: March 6, 2026
Acceptance of Terms
By downloading or using Slow Them Down, you agree to these terms. If you do not agree, do not use the app.
Intended Use
Slow Them Down is a tool for estimating vehicle speeds on residential streets. It is intended for informational and community advocacy purposes only.
Accuracy Disclaimer
Speed estimates produced by Slow Them Down are not certified measurements and should not be used as evidence in legal proceedings. Accuracy depends on proper calibration, camera angle, and video quality.
User Responsibility
You are responsible for your own safety when recording near traffic. Do not operate the app in a manner that endangers yourself or others. Comply with all applicable local laws regarding recording in public spaces.
No Warranty
The app is provided “as is” without warranties of any kind, express or implied, including but not limited to warranties of accuracy, fitness for a particular purpose, or availability.
Limitation of Liability
To the fullest extent permitted by law, the developer shall not be liable for any damages arising from your use of or inability to use the app, including any reliance on speed estimates produced by the app.
Changes to These Terms
Updates to these terms will be reflected on this page with a revised effective date. Continued use of the app after changes constitutes acceptance of the revised terms.
Questions or concerns? Contact itsmeduncan+slowthemdown@gmail.com.