Graph showing average daily use of D.C Metro

This is the graph showing average daily use of D.C Metro. The left is number of people and below is the time axis. Initially, the number at 6 am was the lowest point of 100, then it increased sharply, reaching a peak of 400 at 8am. Later, it began to go down steeply till 10am about 200. Subsequently, there is a plateau between 10am and 4pm, the statble part of which is about 300. And 4pm is the lowest point of a whole day then the number shot up . Till 8pm, the number peaked up to 400, which is the second highest point of the whole dy. The curve between 4pm and 8pm was also a spiked one like the period between 6am and 10am. Till 8pm, it is the third lowest point and then the number slightly rose to 180 at 9pm and then fell down to 120 at 10pm.
According to the graph, there are two spiked period in a whole day: on and off working.