here is a useful knowledge base article.
But to answer your question, the "roll" is directly related to the frame rate, so the higher the frame rate, the faster the "roll".
The difference in when the first row of the image is exposed vs. the time the last row is exposed is roughly 1 second divided by the frame rate.
the "roll" at 30FPS would be about 33ms (1s divided by frame rate). The faster the sensor the smaller the roll, so if the sensor is running at 120FPS the the "roll" is about 8ms.
Note that there are security cameras out there where the sensor runs at a particular frame rate, but is not sending every image. If you want to reduce the effects of the rolling shutter, you should select the highest frame rate possible and adjust the "broadcast" frame rate according to your needs.
Of course, the best is to use a camera with global shutter and have triggering capability, so that you get the vehicle exactly where you need it and not worry about rolling shutter. Monochrome cameras also provide higher resolution images, as you don't have to worry about the resolution loss due to the Bayer pattern used to get color.
I could probably do a full course on how to use machine vision cameras in traffic, biometrics and other security applications :)