Statewide transportation planning needs require forecasting and assessing property damages that result from a road project. As the traffic flow and traffic demands in Idaho change, the Idaho Transportation Department continuously evaluates transportation elements of comprehensive plans, determines impacts of proposed land use changes, and determines the transportation needs for the state. Meeting transportation needs often requires building or widening roadways, which necessitates that the state exercise their eminent domain right, the right to take private property for a public use upon payment of just compensation.
Two basic forms of damages have been identified in eminent domain litigation: the taking of the physical property; and concluded hypothetical damages occasioned by the taking to the remainder—the remaining land and improvements as they exist at a point in time after the road project has been completed. The problem in the past has been that the methods used to estimate the value of these damages employed limited comparable data, usually three to five direct comparisons, with subjective adjustments applied based on experience and arbitrary judgment.
In this study, a six region forecasting model was developed to explain residential property values in Idaho based on multivariate regression analysis. The model uses factors, or characteristics that commonly affect the sales price of a home, and less common characteristics such as street-traffic classification and setback from the street or road, to conclude what portion of home value is attributable to proximity and to street-traffic classifications.
A multi-regional or state wide model was developed and tested, as were separate models for each region. The regions from which data were collected and analyzed are: the Idaho Falls region, the Pocatello region, the Boise region, the Lewiston region, the Moscow region, and the Coeur d’Alene region. The statewide model, which incorporates statstically estimated adjustments for each region, was the strongest and most complete model. With it, statistically reliable as-is and hypothetical estimates of residential property values can be calculated within the tested regions statewide for residential properties that have been or will be affected by damages associated with designing new routes or widening existing streets and roads. The model will also assist in providing more quantative benchmarks for assessing whether damages have even occured at all.