A taxi driver needs to meet its quota for the day or they can't take home somethign for their family. That is why; you often see them on a rush. They need to get more customer to pay not only for the repair, gas, daily quota , but also the money that they can take home ot their family.
The idea here is to meet the quota for the day. The daily quota varies and you need to complete them all to advance to the next level. But, you can always make sure that it involves delivering your customer to their destination. You also need to chek your gas to amke sure that you won't run out of it.