We have an owner who refuses to park their vehicle completely in their driveway and off the association's road.  This is causing problems for snow plowing as well as poses a potential problem if we need emergency vehicles to get beyond the parked vehicle.  We have tried to reason with this person, but they continue to park at least part of their vehicle in the roadway.  Does anyone have a suggestion on how to create a policy that would allow us to legally tow the vehicle?

You should be able to get law enforcement to use one of the following statutes.

Title 17 section 2802 lists various nuisances, including the following:

"... the obstructing or encumbering by fences, buildings or otherwise of highways, private ways, streets, alleys, commons, common landing places or burying grounds are nuisances within the limitations and exceptions mentioned. ..."

Here's a link to the complete statute:  

https://legislature.maine.gov/statutes/17/title17sec2802.html

The ambiguity in that is the question of which definition of the term "private way" is intended in this statute, since Title 17 does not define the term.  In Title 23 section 3021, a "private way" is defined as a "public easement," which would mean it doesn't apply to private roads.  But in Title 29-A section 101 paragraph 58, there is this even more ambiguous definition: 

 58.  Private way.  "Private way" means a way privately owned and maintained over which the owner may restrict use or passage and includes a discontinued way even if a public recreation easement has been reserved. 

According to that definition, a private way may or may not be a road that's open to the public. 

But in Title 17 there is also this statute:

17 MRS §3853-C. Trespass by motor vehicle; civil violation

1.  Violation.  A person may not park a motor vehicle or allow a motor vehicle under that person's control to remain parked:  

A. In a private drive or private way in a manner that blocks or interferes with the free passage of other vehicles without the permission of the owner of that private drive or way; or  

B. On a public highway in a manner that blocks the entrance to a private driveway, gate or barway.   

2.  Penalty.  A person who violates subsection 1 commits a civil violation for which a fine of not less than $500 must be adjudged.  

3.  Registered owner's liability for vehicle.  There is a rebuttable presumption that a registered owner of a vehicle involved in a violation of subsection 1 has that vehicle under that person's control.  

https://legislature.maine.gov/statutes/17/title17sec3853-C.html

That seems pretty clear - a person may not block someone's access, even if that access is entirely privately owned.  I would suggest printing that off and having a copy of it handy in case law enforcement isn't sure what they can do.