That may depend on how your road association bylaws are worded, or it may necessitate an amendment to your bylaws if they don't cover it.  When our road association was formed, they specified in the bylaws which roads they maintain, and that each OWNER pays one fee.  This raised questions of fairness when someone subdivided along the road, because we then had a person paying once for several lots, and the law specifies that each OWNER pays a share, but each PARCEL represents one vote.  Since we had voted to charge each owner the same amount, if we had considered each lot to be a separate parcel, the owner could potentially have voted several times while only paying one fee.  But since there was no added road mileage and no increase in traffic until a lot sold, and since the sale of each lot increased our membership and resulted in another fee being paid, it worked out okay.  We just continued to consider it one parcel with one owner until a lot actually sold. 

Now there is a second small subdivision, which built a road of its own, off from the roads our road association maintains.  That road is not maintained by our road association, but each lot owner pays one fee to our road association for their use of our road to access their road.  If they want their road maintained, they will have to either just pitch in on their own, or form another road association and pay dues to both. 

I have heard of one similar situation where the main road association collects dues from everyone and then returns a portion to the smaller road association for them to use to maintain their road.  It can get complicated trying to figure out what is a really "fair" formula.  There are so many variables that could be considered - mileage of road used, frequency of use, weight of vehicle, assessed value of property, etc. etc. etc.  Fortunately the law doesn't define what is "fair," so long as your formula is applied the same way to everyone. 

Charging each owner the same amount is certainly the simplest way to figure it.  The next simplest is probably to charge one rate for developed lots and one rate for undeveloped lots.  Some charge one rate for year-round use and one for seasonal use, but that can run into questions if a "seasonal" owner comes up in the winter.  The developed/undeveloped option works well because the owners of undeveloped lots usually make little use of the road, so they don't contribute much wear and tear.  But if they have their property logged, or if they bring in contractors to build a house, (especially during mud season,) they can do considerable damage to a road.  Our road association has been considering amending our bylaws to require either a bond or a flat fee surcharge in such cases.

I hope this helps!