Lead was first added to gasoline in the U.S. in the 1920’s to prevent pinging or knocking, From the beginning there were concerns about health effects but it wasn’t until 1976 that a gradual phaseout of lead from gasoline was initiated. Finally, in 1996 leaded gasoline was banned, with some exceptions.
The result of all those years of cars using leaded gas resulted in lead settling on soils, especially near busy roadways.
My suggestion is to test all soils near highways where children are likely to play and remove the lead. Lead levels in children (and adults) decreased substantially after leaded gas was phased out but this lingering lead in soil should still be removed considering that lead is believed to lower IQ’s in children and children can be affected by lead in contaminated soil by touching it or breathing it in.