Access to neighbors property

[Gary Wegmann]

I own a property with outstanding views of the Mississippi River in NE Iowa.   The river in this location is nearly 2 miles wide.   There is a 50' railroad easement between my dwelling and the river although my property line extends to the normal water line of the river.  In other words the railroad holds an easement over my land.     There is another cabin located approximately 3/4 mile upstream.  The neighbors have owned the property for around 20 years while I've owned mine 7 yrs.     The neighbors have access to their cabin from the Mississippi River but have no road access.   From my perspective, the river is the only legal access they have and they knew that when they purchased the property.   

 The neighbors have been driving past my property over the railroad right of way ever since I've owned the property.    The railroad says they have a no tolerance policy which restricts anyone from trespassing on their right of way.    The neighbor claims he has the legal right to drive through the RR right of way to get to his cabin and also to park on the ROW.   I maintain  the neighbor has NO legal right to trespass on the RR right of way, whether it's to walk, fish, park or commute to his cabin.    When I took title to my property I agreed to accept title with the understanding the RR held an easement through my land, but NO ONE ELSE.    Keeping in mind the neighbor can access his property from the Mississippi River, can I legally stop the neighbor from crossing my land or does the RR have jurisdiction since they hold the existing easement  (even though it's my land).