There are an endless number of places where the speed limit data does not match the actual speed limit. My car has the speed limit wrong on hundreds of small back roads and even segments of highway. This encourages not actually paying attention to posted signs.

Failing that, you can be going the speed limit and then the speed limit drops or increases by 15-30mph suddenly. Like highway ramps for example. Most people coast into the lower speed after the change or accelerate into the new speed in advance of the change. This would encourage hard breaking at extremely dangerous places or entering highways at incredibly unsafe low speeds.