To easily import a Carlson file, you can use this Text Import Wizard (TIW).
If you would like to add this TIW to the Import Survey Data Dropdown Menu, refer to the following wiki:
http://communities.bentley.com/products/road___site_design/w/road_and_site_design__wiki/add-tiw-to-the-import-survey-data-dropdown-menu.aspx