Is there a GPS device that can be used on the road for directions and also on the golf course for yardages?

Nope

There are clubs whose golf carts are equipped with GPS and some who had the system and discarded its use. The system which ran off the electric cart batteries caused many cases of discharged batteries which stopped the carts and the GPS from operating. Personally, I have used the system on two courses and found it very beneficial especially for the first time playing the course. The management has indicated that they must keep a cart usage program to spread useage, to make sure that all carts are properly recharged and that GPS systems are off when not in use.

as of this moment, no. But just wait - your cell phone will have GPS with golf course capabilities (likely download for a fee) within 2 years. Mark my word!

yes i have one it is called a skycaddy, it tells me how far out i am and where different bunkers are or other helpful information about the course and the yardage.