Why Highways Are Less Harmful In Parks Than On Urban Streets

When I read Robert Caro's The Power Broker (a biography of New York road-builder Robert Moses), one story that didn't quite make sense is Caro's discussion of the Henry Hudson Bridge. Caro writes that Caro's routing of this bridge caused "the destruction of Manhattan's priceless last forest" in Inwood Hill Park.  But I visited the park yesterday afternoon, and it didn't look at all "destroyed" to me.  Inwood Hill Park is still one of the jewels of Manhattan's park system, full of primeval-looking forest.  (more photos here). 

Why wasn't the bridge (or the nearby parkway) as destructive as Moses' highways were in some urban neighborhoods? It seems to me that parks and neighborhoods are very different, for two reasons.  

First, a typical urban street is small enough for the highway to cover the entire street.  By contrast, a large park (such as Inwood Hill) is far larger than an urban street, and thus a bridge or highway might make a much smaller impact by comparison.  

Second, a highway has a far wider group of impacts upon a street than upon a park.  The major impact of a highway in a park is noise, which (in a park as large as Inwood Hill) does not extend throughout the park.  By contrast, a highway may have a much wider variety of impacts in an urban neighborhood: it may require destruction of dozens of homes and business, which in turn means that businesses relying on the residents of those homes lose money.  And the people displaced by the highway will create overcrowding if they move to nearby streets, or cause neighborhood businesses to lose customers if they move far away.  Thus, an urban highway through a neighborhood is far more toxic than a highway in a large park.