Gizzy
A gentleman, a scholar, and a railway modeller....

You will need the R5 curves to make a passing loop.
Here's a linky to Piko's track Geometry....
http://piko.de/produkt_db/check.php?page=g-geometriebeispiele&grand_id=6&parent_id=3&sss=3
Here's a linky to Piko's track Geometry....
http://piko.de/produkt_db/check.php?page=g-geometriebeispiele&grand_id=6&parent_id=3&sss=3