Google Maps - Get Directions

Hi All,
To date i've implemented the following on the View As Custom for my field 'start_town'
global $data;

$value = "<a target=_blank href=\"http://maps.google.co.uk/?ie=UTF8&hl=en&q=".$data["start_town"]."; \"> ".$data["start_town"]."</a>";
This works 100%.
However, on to the next stage....
Does anyone know what the code would be for the "Get Directions" part of Google Maps.
Table: Posting

Fields: start_town, end_town
Thanks in advance
Lisa