Is a speed limit actually effective?

While speed limits are posted to protect drivers and pedestrians from the dangers of driving and roadway conditions, they often don’t have a significant effect on actual driver speed. The reason is that most drivers are familiar with an appropriate speed for the particular road they are on, and when traffic engineers install a speed limit, it is often close to what people are already going. Limits that are too low will often make even the most law-abiding drivers violate the speed limit, so engineers take into account the proper speed for the area.