Final answer:
It is required by law to slow down to the posted yellow ramp speed by the time you reach the sign when exiting an interstate for safety reasons and to avoid vehicle control issues and potential accidents.
Step-by-step explanation:
When exiting an interstate, it is required by law to slow down to the posted yellow ramp speed by the time you reach the sign. The speeds indicated on these signs have been determined through engineering studies and account for factors such as the sharpness of the turn on the ramp, the grade, and other conditions that could affect vehicle handling when decelerating from highway speeds. Ignoring these signs and maintaining highway speed could lead to loss of vehicle control, increasing the risk of accidents. Therefore, for safety reasons, you should always decelerate to the suggested ramp speed before you reach the sign.