THE ECOLOGICAL ROAD-EFFECT ZONE FOR TRANSPORTATION PLANNING AND MASSACHUSETTS HIGHWAY EXAMPLE

Ecological flows and biological diversity trace broad patterns across the landscape, whereas transportation planning traditionally focuses carefully on a narrow strip close to a road or highway. To effectively mesh the ecological dimensions with human mobility objectives the "road-effect zone", over which significant ecological effects extend outward from a road, appears to be central. The zone is many times wider than the road (with roadsides/verges), is strongly asymmetrical, and has convoluted margins. The road-effect zone is illustrated with a 24 km length of a four-lane highway in the outer suburbs of Boston. The locations and distances of effects of nine processes are measured or estimated, and mapped to show the road-effect zone. Factors such as road salt affecting vegetation only extend outward meters or 10s of meters, whereas the effects to traffic noise on bird communities and the road as a barrier interrupting wildlife travel corridors extend outward 100s of meters to kilometers. Roads and roadsides cover approximately 1% of the United States, and based on calculations using scattered data, it is estimated that 15-20% of the land is directly affected ecologically by roads and vehicles. Thus the road network causes an enormous impact on America's ecological infrastructure. A vision for America's future transportation system focuses broadly on the land uses, landscape ecology and the road-effect zone in transportation planning, and provides effectively for both (a) natural processes and biodiversity and (b) safe and efficient human mobility.