Research Idea Details

Research Idea Scope

Major and visible effects-such as shoreline alteration, reduced connection to adjacent upland, sediment filling-in, eutrophication, reduced oxygen levels, and altered fish populations-are attributable to roads altering coastal, lake, reservoir, pond, and vernal-pool ecosystems. Similarly, stream and river water quality is significantly altered by roads, as illustrated by bridge effects, eroded sediments, turbidity, reduced diversity of stream habitats, warm water from roadside ditches, movement of chemical substances, truncated food webs, and altered fish populations (FHWA 1996; Findlay and Houlahan 1996; Evink et al. 1999). However, a broader view of the cumulative impacts is critical. Transportation systems provide a major mechanism for dispersing human influences across the landscape. This dispersion begins with single pathways, expands to networks, and culminates in increasing release of contaminants and corresponding environmental damage around the networks. The cumulative effects of transportation systems on water quality, considering all points of corridor-waterway interaction, must be recognized. Such a cumulative-effects analysis would go beyond simple toxicity determinations or parameter-specific regulation to examine the effects, both small and large, of water quality change over expansive spatial and temporal scales, focusing in particular on the functioning of aquatic ecosystems.

An extensive literature on the hydrology of transportation systems includes the effects of roads on water and of water on roads. The contaminants in highway runoff have also been widely characterized, though much remains poorly known. For example, the specific ecosystem effects of highway runoff and their relative contribution to overall environmental quality in receiving waters remain elusory. The situation is complicated by the fact that some effects of highway runoff are site-specific, while others are general; moreover, runoff may exacerbate problems created by other activities in watersheds. Although general consequences may sometimes be predicted, the information available on the aquatic effects of roads often is inadequate to support effective planning. For example, although contaminant loading can be estimated, regulatory authorities often require site-specific studies, which seldom follow a uniform protocol that would permit extrapolation to other sites. Research on certain aquatic-ecosystem processes operating over decades and centuries, as is the case with road systems, also would enhance extrapolation for planning. Thus both the state of knowledge and transportation planning would be advanced by conducting broader analyses of cumulative effects instead of the narrower analysis of transportation-related effects.