Many students who commute to college believe that the amount of time they spend in transit has a marked effect on their lives.

I managed to find this exercise online - you had to choose indirect and direct quotations in reported speech.
The sentence you wrote above is the correct option - you don't have to use the quotation marks in this case. If the sentence said: Many students who commute to college say the following: "The amount of time we spend..." then you'd have to use quotation marks, but in this case, you don't.