Imagine you are driving down a county road at 60 mph. One half mile in front of you, you see an object: a tractor, or a combine, or a truck pulling a wagon of hay, or a bicyclist, or an Amish buggy. That object is going 15 mph in the same direction as you. In 52 seconds, your car is going to catch up to the object.
Now, imagine the distance you see the object is only a quarter of a mile. The amount of time you have to react is now only 26 seconds.