Resolution is NO guarantee that you will get the license plate. You also need a very high bitrate.
If a car is passing you at 60 MPH, you almost certainly will NOT get the license plate unless you're running a ludicrous bitrate, chewing up gigabytes in minutes. Video codecs work by taking a keyframe and each subsequent frame is just differences from the previous frame, and there are only so many bits per frame to do that. When cars are passing you quickly, freeze frame will just result in blurs, even when you have a high shutter speed (bright light conditions) because there just aren't enough bits to get all the data in the frame that changed.
For people in cities or winding country roads where traffic is only maybe going 10 or 20 MPH faster than you are, this may be true.
For me it's actually better in most conditions to run 720p, which is high enough resolution to get plates, but I'm not wasting bitrate on useless resolution instead of on frame diffs.