Can you build a road or stoplight on your property.?

When property is developed, that is when it's taken from raw land to some kind of improved land, the authorities having jurisdiction (AHJ) require certain parts of the development to be done so that the public is protected. This means that the AHJ determines whether a road is required or not, A civil engineer designs how the road will be run, whether it has sidewalks, streetlights, stop signs etc., etc.. The plans that the civil engineer creates are then submitted to the AHJ for approval and comment. Then the approved plans are issued as construction documents to a construction firm. Then the road gets built per the plans. This process turns raw land into Civilized land. This process usually results in the property being worth more. That's why the property owner wants to do it.

Sure, as long as you are not violating any zoning ordinances. Office parks and shopping centers do it all the time