Coastal roads provide access to the lake shore, including shoreline in less developed areas and sensitive habitats. Though similar to coastal development, roads are considered a distinct stressor because they:

• Add to the amount of impervious, in impermeable, surrface area
• Alter the nearshore physical and chemical environmnet by contributing run-off polluted with road surface materials (e.g., salt, sand)
• Fragment habitats
• Act as barriers to animal movement

Mapping coastal roads as a Great Lakes stressor

Canadian road data was derived from the Ontario Road Network.¹ U.S. road data was derived from TIGER line files from the 2010 U.S. Census. For consistency, efforts were made to select paved roads from each dataset.²

The influence of coastal roads was assumed to extend one kilometer into the lakes. For each 1 km² shoreline pixel, we computed the coastal road density (km road/km²) and assigned the value to the nearest water pixel. High coastal road density is generally correlated with high human population and high urban development.³

Spatial distribution of coastal roads as a stressor in the Laurentian Great Lakes (Inset: Southern Lake Michigan).