Building on the comment about lead (Pb), other metals such as Cadmium and Zinc are common alongside roads, and especially PAH's (polycyclic aromatic hydrocarbons) that are made from the burning of fossil fuels (so car exhaust!) and deposited within 25m of roadways and bind in the soil. A good thing to consider is how the folks living near there would be exposed to contaminants as a result of the huge increase in traffic from the overpass. Are they growing gardens near there? Are children playing near there in the soil?
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There's a community who lives just off or, nearly under the overpass- as in, they look directly up at it at probably an 85 degree angle, so children play there. There are also some gardens, and a small intersection with a green way with a field there where children often play.