Transportation activities generate a wide range of pollutants, including particulates, copper (Cu), zinc (Zn), and lead (Pb), that accumulate on roadway surfaces. Stormwater runoff can flush these species to, and impair the hydrology of, receiving waters. This study evaluated the ability of roadside infiltration, a management strategy that relies on natural dispersion and permeation of runoff through roadside soils, to mitigate the impacts of roadway runoff in semiarid eastern Washington. Monitoring of nine runoff events totaling 60 mm of runoff showed complete infiltration within 2 m of the roadway edge. Levels of Cu, Zn, and Pb in the aqueous phase of runoff ranged from 10–200 mg=L, while levels in sediments ranged from 20–75 mg=kg (dry weight). Two-thirds of Cu and Zn in runoff were associated with the aqueous phase, while two-thirds of Pb was associated with sediment. The midsized fraction (0.5–2.0 mm) of sediment in runoff contained the greatest mass of metals (around 40%). While Cu and Zn in roadside soils were slightly higher at the roadway edge, all concentrations were near or below background levels. In contrast, Pb concentrations increased with depth and distance from the roadway, likely the result of historical deposition and=or Pb leaching from deicing salt applications. From a management perspective, results suggest that: (1) roadside infiltration is a suitable method to manage the environmental impacts of roadway stormwater runoff in semiarid climates, and (2) the midsized fraction of roadway sediments should be targeted for capture because they contain the greatest mass of metals.