I was wondering which preposition is more idiomatic here:
To get a shuttle taxi all you have to do is to stand beside the street and just look interested. If a taxi driver wants to pick you up, ..... speed(s) down and turn(s) close and the driver looks at you.
a. he / she
To me they all work properly, but it is important to define which one sounds more idiomatic to native speakers so that I know weather I have to add the third person "s" at the end of the following verbs or not.
You can use "it", which would be taken to refer to the taxi itself. If you use "he", "she", or "they" you would not also use "the driver" later on; you might say "and then look(s) at you". These days "they" with the plural forms of the verbs is probably the best choice.
Please note my comment about other aspects of the sentence as well.