That is a very ambitious project for someone who is new to LabVIEW. Is this a school project?
Have you taken any tutorials or classes on LabVIEW? Do that before you even begin thinking about your project.
Once you are ready, start working on individual aspect of the projects. Make simple VI's that can communicate with your range finder and detect the presence or absence of cars.
After that look up "state machine architecture" within LabVIEW and the forums. Also search the forums for traffic light projects because this seems to be a common school assignment and you'll find examples you can peruse and try to understand.