Garmin Edge Touring can't do car, walking, or straight-line routing directions?
There is a website called http://www.dcrainmaker.com please check out page http://www.dcrainmaker.com/2013/08/garmin-touring-computer.html for the full guide however to answer your question and encase it disappears;

You can also specify if you want to start the route from where you are, or from another point on the map.

Once you’ve given it some instructions it’ll go off and come back with three routes (it’s like Monty Python – everything is in threes).  It did take a bit of time (perhaps 2 minutes) to come up with the routes.  Each route is roughly the distance you’ve specified, and all routes come back to where you started.

You can select any given route option to get a map overview:
There are a number of settings around routing and navigation within the options (applicable to round trip routing and generic routing), including how the unit routes and whether it, for example, minimizes routes with hills. This point here is were you select routing mode. it's not everything you were after but should give you a good help towards it. 

Full specifications for the device, versus other devices, are at the bottom of his page.