Living near a road and what reaches your garden

The Census TIGER/Line PRISECROADS database catalogs every interstate and US/state highway in the country — the regional contamination signal sitting closest to the most American gardens. Vehicles emit lead from pre-1986 leaded gasoline still bound in roadside soil, polycyclic aromatic hydrocarbons (PAHs) from incomplete fuel combustion, and fine particulates carrying heavy metals from brake and tire wear. The EPA's Near-Road Air Quality 2010 evidence shows concentrations are highest within about 100 ft of the road edge, drop roughly 70–80% by 500 ft, and reach near-background by 1,000 ft. Wind direction shifts the picture: downwind soil carries 2–3× higher concentrations than upwind soil at the same distance.

This is one of the most readable contamination patterns in the federal record — distance does most of the work. The air at 650 ft back from a major road is meaningfully different from the air at 100 ft: same source, very different exposure. For most parcels beyond the 500-foot EPA threshold, this is a "good to know," not a "must mitigate." Wind direction sharpens the read further — a parcel upwind of a busy highway sits in a different exposure profile than a downwind one only meters away. The map encodes both axes, so you see the asymmetric plume shape, not just the proximity dot.

For gardens within 500 ft of a major road, raised beds with imported clean soil sever the soil-contact pathway — the most direct mitigation. A dense vegetative buffer (hedge or treeline) between road and growing area reduces particulate deposition further. Crop choice carries weight too: leafy greens accumulate the most surface deposition and warrant the larger setback; fruiting crops with peelable skins accumulate the least. If you grow in native soil within the 500-foot band, a soil test for lead is the right starting point, and liming acidic soil to pH 6.5+ binds lead and reduces uptake. Wash leafy greens under running water before eating — most surface deposition rinses off.

1. 1For parcels within ~500 ft of a major road, prioritize raised beds with imported clean soil for soil-contact crops.
2. 2Plant a vegetative buffer (dense hedge or trees) between the road and growing area to reduce particulate deposition.
3. 3If using native soil within 500 ft of a major road, test for lead — pH-adjustment to >6.5 reduces lead bioavailability.
4. 4Wash leafy greens grown near roadsides under running water before consumption to remove deposited particulates.
5. 5Roadside contamination decays with distance — gardens >1,000 ft from major roads have near-background exposure.

Frequently asked questions