Thanks to a recent GoogleMaps API update that added the “AvoidHighways” option on driving direction results, now the builder automatically create tracks avoiding highways.
Now you can view tracks with Google Earth, directly into your browser. No need to download the KML file and then open Google Earth application.
To view a track in 3D, simply press the EARTH map type button, at the top right of the google map (ssved tracks only)

From Google Geo Developers Blog :
Bug: after viewing a track with Google Earth plugin, next tracks (usually loaded with AJAX calls in the same page) aren’t displayed correctly; firefox also signals a lot of javascript errors. To avoid this, after viewing a track with Google Earth plugin, press menu TRACKS in order to reload the page.
As a alternative to export tracks in KML format and then use Google Earth, now you can use Virtual Earth 3D (Beta) and display tracks in 3D, directly in your browser.

To do this, first display a saved track, then select “Virtual Earth” in the map provider combobox and wait some seconds in order to load API (in IE, after a info dialog, you must reselect Virtual Earth again).
The Virtual Earth map appear. Now press 3D in the toolbar (note: in firefox, for some strange reasons, labels are hidden! Move the mouse near the VE’s toolbar and click when the tooltip indicating 3D map appear).
If not yet installed, a popup window will help you in installing the plugin