Consider the two rules - the old rule where each homeowner is responsible for his part of the sidewalk, and the new rule where the person with the best snowblower is responsible for the whole block. In the short run - say, for the first week after the neighborhood association meeting - which rule (if either) would be more efficient if  transaction costs are low? What if transaction costs are high? 
In the longer term - say, over the course of years - which rule would lead to people owning more advanced snow clearing equipment? Which rule would be more efficient in the long run?