You can feel the presence of a living body of water, even when you can't see it. The vegetation, the light, the wildlife, all announce that you are now entering the riparian zone.
The presence of a busy motorway -- just yards beyond the trees beyond the viaduct -- is somehow less obvious. Apart, of course, from the constant noise. There is no transitional zone, no distinctive ecology, although it's true the motorways themselves are becoming an ecosystem in their own right. The bounty of roadkill along the central reservations and verges is one reason for the rapid spread of carrion eaters like the Red Kite, I'm sure.
Maybe it's that lack of a distinctive sense of transition that leads
pheasants, foxes, badgers and deer to stride boldly out across the
carriageway. After all, you don't see a constant flow of such creatures floating
downstream, Eeyore-like, having mistakenly tried to dash across the