Oracle Database Discussions

This is a newbie question I know, but it's one I'm curious about and am stuck in an argument over. Say you have two tables: Vehicle and Driver. The Vehicle table holds the vehicle information and the Driver table holds the driver information. And they are linked by a one-to-one relationship. Now my supervisor says that since they are one to one we should just make them one table because performing a join on those two tables will slow down the web app that is running on top of them. My thinking is keeping them two tables makes more sense conceptually. Easier for someone new to the table structure to learn and already primed for object oriented programming to go on top of them. Seems to me combining them into one table would just confuse the data. And in my opinion since the tables are in the same table space the delay from the join should be so minute that the user will never notice. So my question is is there some standard rule that says one to one's should be combined and is there ever a case where the join would be noticeable enough to worry about? Sorry, guess that's two questions in one.

Thanks in advance,
John