I do not think it would be rude at this point to send another polite email. You could wait a couple more days if you like but I wouldn't wait too long. Just say something along the lines of how excited you are about the project without focusing on the time since you sent your last email.
Does he have an assistant / secretary? If so another approach would be to contact this person and say you would like to set up a meeting to talk to doctor X about the research project.
Finally, is there a way you could "accidentally" run into him?