Yes, you can say “backing up” and it means that you're moving backwards. You can use the prepositions “up” or “down”, depending on the context.
If the street doesn’t slope then you can use either “up” or “down” and they both mean
If the street slopes, then it makes most sense to use “up” and “down” so that they also describe the vertical direction in which you are moving, so that
up=towards a higher position, from a lower one
down=towards a lower position, from a higher one