Busy roads, rail lines and substations: assessing external factors
Mass appraisal often misses what is next door. It is a documentable argument.
Mass appraisal models price a property from its own characteristics and its neighbourhood. They are much worse at noticing what is next door — and that gap is a real and under-used argument.
What counts as an external factor
- A busy arterial road, particularly where the property fronts it
- A rail line, freight yard or level crossing
- An electrical substation, cell tower or high-voltage line
- Commercial or industrial use immediately adjacent
- A flight path
- A landfill, sewage works or similar
- Backing onto a car park, loading bay or fast-food drive-through
Why the model misses them
A valuation neighbourhood is a polygon. Every property inside it is priced by the same relationships. The model has no way of knowing that the four properties along the eastern edge back onto a rail line while the other two hundred do not.
The market knows. Those four sell for less. But if they rarely sell, the model never learns it.
The argument
This is a uniformity argument, not a market-value one, and framing it correctly matters. You are not saying the neighbourhood is overvalued. You are saying your property is assessed at the neighbourhood's general level while carrying a burden the general level does not reflect.
The comparison that makes it: your assessment per square foot against properties in the same neighbourhood that do not have the factor. If you are assessed the same as houses two streets in, that is the disparity.
The evidence that works
- A map showing your property and the factor. One image does most of the work.
- Photographs from the property, dated, showing what you actually look at.
- Traffic counts, published by many highway authorities.
- Sales evidence, if available — properties on the road against properties behind it.
- Your comparables table, with the affected and unaffected properties distinguished.
What weakens it
The factor predates the neighbourhood. If the rail line has been there since 1890, it is arguably already in the general level of value for the whole area, and the model may well have learned it. Recent arrivals are stronger arguments.
Everyone has it. If every property in the neighbourhood fronts the same road, there is no disparity within the group — you would need a market-value argument against a different area instead.
You cannot show it in numbers. "It is noisy" is not an argument. "Four properties fronting the road are assessed at the same $15.96 per square foot as the interior of the neighbourhood" is.
The honest framing
Offices hear a great deal about traffic and noise, most of it unquantified. A filing that presents the factor on a map, identifies which comparables have it and which do not, and shows that the assessment does not distinguish between them is doing something different — and it is the version that gets granted.