Speed Log A custom build by Tahuya River Software

Speed Log: case study

The problem

"People drive too fast through here" is an easy thing to say and a hard thing to show. Radar guns cost money, their readings aren't saved anywhere, and a board or a city office wants more than a few neighbors' impressions. Most people already carry a camera that films hundreds of frames a second, but turning a video into a number someone else can check takes careful work.

What we built

Speed Log uses two-line timing. You measure two points on the ground with a tape and film each car passing them in slow motion. In the app you step through the video a frame at a time and mark when the front bumper reaches each point. Distance over elapsed time gives the speed.

Each measurement goes into a log, along with a frame showing the car and the numbers behind the result. When there are enough to show a pattern, one read-only link shares a report with charts by hour and day, the marked frames, and a plain explanation of the method. The log exports to a spreadsheet or a PDF.

The awkward parts of working with phone video are handled on the server, so the person using it only sees frames and buttons.

A phone in slow motion isn't the only option. Park with a dash camera recording at 60 fps, or export a clip from a security camera, then upload the footage and mark each car the same way. Any frame rate works, but higher rates give a tighter range: for a car at 25 mph over 45 feet, that's about ± 0.2 mph at 240 fps, ± 0.7 mph at 60 fps, and ± 1.4 mph at 30 fps. Footage from a moving dash camera can show the speed of the vehicle it's in, but it can't measure another vehicle, because that would be two moving targets.

Showing its work

Every speed comes with a range, because each mark could be one frame early or late. A report shows that range and the figures behind it, so a reader can redo the arithmetic.

How close it gets

These are estimates from video, not radar or lidar readings. One test clip isn't a certification, and the results aren't meant for citations.

The build

Speed Log is a stand-alone project, separate from our towing software.

Have a job a spreadsheet or an off-the-shelf app doesn't quite do? Email info@tahuyariver.com.

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