To determine which time interval has the fastest running speed, we need to calculate the average speed for each interval.
For the interval [0, 8], Riley ran from 0 miles to 1 mile in 8 minutes, giving an average speed of 0.125 miles per minute. For the interval [2, 11], she ran from 0.4 miles to 1.5 miles in 9 minutes, which is 1.1 miles in 9 minutes, resulting in an average speed of approximately 0.122 miles per minute.
Thus, Riley ran faster during the interval [0, 8] since her average speed of 0.125 miles per minute is greater than her average speed of 0.122 miles per minute in the interval [2, 11].