The Contour Roam sounds like a good buy.

I've used an Ion Speed Pro for almost a year. It has no significant shortcomings considering the price (well under $100, usually closer to $60) and self-contained weatherproofing (it doesn't need a weatherproof housing, as long as the rear cap is in place).

But the Ion Speed Pro battery runs only about 90 minutes. Beyond that I need to hook up an external USB battery, which compromises the weatherproofing -- I need to detach the sealed rear cap to access the USB port, which exposes the control panel and media card slot to weather.

Unfortunately most of these are action cameras, not ideal for traffic documentation. Action cams have ultra-wide angle lenses, nearly fisheye -- around 150-180 degree diagonal FOV. Great for ultra close action and non-critical aiming. But fine details like license plates tend to be obscured. Ideally a forward facing bike/helmet camera would have a diagonal FOV of around 90 degrees.