Road Ecology Center

An extensive area of frequently mowed open grassy roadsides is designed for highway safety, yet paradoxically, in many locations woody vegetation of various types may make safer highways, and additionally provide diverse valuable benefits for society. Therefore our objective is to identify the goals of greatly increasing woody vegetation, consider the pros and cons, and identify the especially desirable and undesirable locations for it. Today, frequent costly roadside mowing favors many non-native species including invasives. Rare species also live on roadsides, including nearly a quarter of the U.S. federally listed threatened-and-endangered plant species with at least one roadside population. The prime goals of greatly increasing woody roadside vegetation are to: (1) increase wildlife habitat, biodiversity, and landscape connectivity; (2) increase highway safety and driver experience; and (3) decrease pollut¬ant and peak-water-flow inputs to nearby water-bodies. The first goal has few disadvantages and also accomplishes diverse societal benefits. The second goal emerges from a modest decrease in vehicle speed in appropriate areas, plus the use of visually diverse types of roadside woody vegetation. An entrée into the travel-behavior and wildlife literature indicates that drivers drive more slowly on narrow than wide two-lane highways, and suggests that a sharp drop in wildlife/vehicle crashes appears between a posted speed limit of 90 and 70 km/hr (55 and 45 mph). The third goal enhances nearby streams, ponds, and other water bodies, mainly by significantly improving conditions in roadside ditches. Tall shrubs or natural forest/woodland are especially desirable vegetation types for >50% of the 35 situations common along road networks. Mowed grass is especially desirable on 17% of the situations, essentially the most risky driving locations. Meadow/low shrubs and small trees with herbaceous layer are intermediate in overall roadside value. We conclude that a massive increase in woody roadside vegetation offers numerous transportation, environmental, and societal benefits with minor disadvantages. Evaluation by a blue-ribbon panel of diverse experts and widespread pilot projects with research and monitoring are valuable next steps.