Dust from an Unpaved Road, Priced per Vehicle: Emission, Exposure at a Roadside House, and the Cost of Three Suppressions per Unit of Dose Avoided

Dust raised by traffic on unpaved roads is usually discussed in general terms: roads are dusty, watering helps, gravel helps. This paper prices the problem per vehicle and per house. Using the emission form published by the United States Environmental Protection Agency for unpaved public roads, a light vehicle of 2.0 tonnes travelling at 40 km/h on a surface with 10 percent silt emits 227.4 g of particles smaller than 10 micrometres (PM10) per vehicle-kilometre after correction for wet days, and a 12-tonne vehicle at 35 km/h emits 476.4 g per vehicle-kilometre. For a road carrying 200 vehicles per day, dispersion modelling places the annual mean PM10 increment at a house 25 m from the centreline at 20.4 micrograms per cubic metre, with 12.9 g per square metre of dust deposited per year. Three suppressions are then priced on the same basis, cost per microgram per cubic metre of annual mean concentration avoided at that house. A 50 mm gravel cap, which lowers surface silt from 10 percent to 3 percent, avoids 13.5 micrograms per cubic metre at an annualised cost of 82 dollars per unit avoided. Watering twice daily through a 180-day dry season avoids 11.22 micrograms per cubic metre at 481 dollars per unit. Enforcing a 25 km/h speed limit avoids 3.97 micrograms per cubic metre; its cash cost is small, but once the value of the travel time it takes is counted, it is the most expensive option at 3,342 dollars per unit. Valuing a one-unit reduction at 40 dollars per house per year, the gravel cap pays for itself wherever there are at least 2.0 houses per kilometre, watering only above 12.0 houses per kilometre, and speed enforcement on time-inclusive accounting only above 83.5 houses per kilometre. On a road with fewer than about two houses per kilometre, none of the three pays for dust control alone, and the honest recommendation there is to spend nothing on suppression.