Slow Them Down
Your road has a speed problem
Only for iPhone
Free · Designed for iPhone. Not verified for macOS.
iPhone
Slow Them Down turns your iPhone into a traffic speed study tool. Record vehicles on your street, mark their positions frame by frame, and get accurate speed estimates — no radar gun required.
How it works
1. Calibrate your camera using a known reference distance (vehicle length, lane width, or a manual measurement)
2. Record a video of passing traffic
3. Select two frames and mark the vehicle's position in each
4. Get an instant speed estimate in MPH
Track every vehicle
Log each measurement with vehicle type, travel direction, street name, and timestamp. Build a complete picture of traffic patterns in your neighborhood over days, weeks, or months.
Automated reports
Generate detailed PDF reports with V85 speeds, traffic volume breakdowns, speed distribution charts, and vehicle type summaries. Filter by street to isolate problem areas. Share reports directly with your city council, HOA, or neighborhood group.
Privacy built in
Faces and license plates are automatically detected and blurred before you share anything. The app errs on the side of caution because a blurred street sign is better than a visible plate. We also don't store the images, videos beyond the processing needed to calculate a speed.
Built for advocacy
Speed data is what cities use to justify traffic calming measures like speed bumps, stop signs, and road diets. Slow Them Down gives your community the same data, collected from the streets you actually live on.
1. Made the frame extraction experience better (Thanks for the feedback Christian!)
2. Added polish around back/edit to make the extraction flow easier (Thanks for the feedback Christian!)
3. #57/#38 Fix Google Play target API level requirements
The developer, Duncan Grazier, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy .
Data Not Linked to You
The following data may be collected but it is not linked to your identity:
- Location
- Identifiers
- Diagnostics
Accessibility
The developer has not yet indicated which accessibility features this app supports. Learn More
Information
- Seller
- Duncan Grazier
- Size
- 4.6 MB
- Category
- Utilities
- Compatibility
Requires iOS 17.0 or later.
- iPhone
Requires iOS 17.0 or later. - Mac
Requires macOS 14.0 or later and a Mac with Apple M1 chip or later. - Apple Vision
Requires visionOS 1.0 or later.
- iPhone
- Languages
- English and Spanish
- Age Rating
13+
- 13+
- Copyright
- © 2026 Duncan Grazier