Does drush have built-in variables or macros?
If you source the file examples/example.bashrc from your ~/.bashrc file, then you can do useful things like cd %root or cd @site:%root.  Without sourcing that file, you can use cd $(drush dd %root).  If you want to go to a module or theme directory, cd $(drush dd %devel) also works.  Using the %path aliases without qualifying them with a @site alias does, of course, require that your cwd be inside some Drupal site (or $options['root'] must be set in some drushrc.php file).