Transportation infrastructure and public safety

Rivers and streams, like transportation networks, are widely spread across the landscape providing many opportunities for intersections with roads. These crossings are points of potential vulnerability for transportation infrastructure. Road-stream crossings are a critical, and sometimes vulnerable, component of the transportation system. Flooding and erosion associated with severe storms can disrupt transportation networks and thus the ability to provide essential services. Crossing failures can be more than an inconvenience; they can threaten public safety and result in significant economic impacts.

Recent severe storms in the Northeastern USA has raised concerns about the vulnerability of road-stream crossings, and transportation networks in general, to flood damage. In 2011, tropical storm Irene resulted in widespread damage to roads and highways in VT, NY and MA, including the failure of over 1000 stream crossings in Vermont alone. With climate change models forecasting storms of increasing severity and a higher frequency of severe storms, state departments of transportation are beginning to take the issue more seriously.

Transportation vulnerability includes three factors:

Risk of failure

A road-stream crossing can fail for a number of reasons, including structural deficiencies or storm damage. Normal wear and tear or specific damage during construction or maintenance activities, or accidents can compromise the structural integrity of culverts and bridges. Undersized structures may lack the capacity to pass enough water during storms to prevent failures due to these hydraulic conditions. Some risks are related to the geomorphology of the site, such as its vulnerability to erosion, sediment deposition, blockage by woody debris, or lateral movements of the stream channel. The magnitude of such failures can range from inconvenience when roads are temporarily closed due to water overtopping the road, to catestrophic failures that result in the complete loss of a crossing, downstream property damage, and loss of life. Severe storms, such as tropical storm Irene, can result iin multiple crossing failures that can impede emergency crews and leave neighborhoods and communities isolated as they are cut off from surrounding areas.

Criticality

Crossing failures during extreme storms and flooding events can impede critical routes and severely disrupt access to important infrastructure and the ability of communities to provide critical emergency services. Impassable roads can prevent electrical line workers, police, fire and emergency medical services from reaching their intended destinations. Road failures can also prevent access to important infrastructure such as water treatment plants, power plants, electrical substations and gas compressor stations, and can disrupt the core functionality of transportation networks. Criticality is a measure of how important, or irreplaceable, a crossing is for providing essential access, transportation functionality, and the delivery of critical services.

Climate change resistance/resilience

Climate change models are forecasting storms of increasing severity and a higher frequency of severe storms in the future. It is important to also take future changes in hydrology due to climate change into account when assessing the vulnerability of road-stream crossings.