Question: 

Can the Finnish/Soviet Player trace road supply over hexside 1513/1514
(Lake Hexside) as there is no bridge at that location?

Answer:

Both Players may trace road supply over that narrow straight hexside even
though the road does not cross the hexside as in hexside 3717/3718, for
example. Think of it this way in warm weather there is a ferry present and
in cold weather the lake is frozen and units can just drive accross. A road
element Line of supply can also be traced accross 1304/1404 but NOT 1303/1402
as the transportation line does not point to that particular hexside.

Source:

Posted by Gary J. Stagliano (EuropaStag@aol.com) on the Europa Mailing List, 2001