This should let you know the difference's between the two, ( check the links )if you use your mouse you can zoom in and see the difference's between the two, check the distances between the wheels and the frame on the Tri bike and it also is lower in the front too give it a more Aero dynamic effect and the frame geometry is different on the tri bike.
The Tri bike is set up for and used for Time Trailing purposes. The road bike would be better suited for riding around town and if you want to off road get a mountain bike.

http://www.trekbikes.com/us/en/bikes/roa...
http://www.trekbikes.com/us/en/bikes/tri...