addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsConsider, for example, a scour critical 23 bridge is potentially vulnerable to moreintense rainfall events leading to increased peak runoff rates, which,hypothetically are expected to increase in likelihood. If the bridge has beenreplaced, or the scour condition has been otherwise corrected through normalrenewal and rehabilitation cycles, by the time rainfall events are likely to exceedhazard thresholds for scour then the issue of exposure might be null. If the asset(or specific asset vulnerability) and the climate hazard are likely to overlap intime, however, then exposure is both physical and temporal and a more detailedassessment of potential consequences may be in order.The extent of the Window – the duration of potential overlap (between asset andstressor) – may prove instructive in formulating a cost-effective adaptationstrategy (or strategies). For example, depending on the region’s risk toleranceand resources, a relatively short overlap between stressor incidence and assetreplacement could be addressed by slightly advancing the date ofreplacement/reconstruction, or by implementing maintenance and operationalstrategies expected to minimize impacts during this higher risk period. Longeroverlaps may pose greater challenges, but often can be addressed through awider variety of strategies (often in synergy), including planning to enhanceredundancy, asset management strategies, engineering interventions (such asretrofits), and more. Broad categories of adaptation strategies are set out later inthis Module.Consider Asset Lifespan and Renewal CyclesAccurate estimates of asset lifespan and renewal cycles can be difficult to obtainin some regions. This data is rarely embedded in systems-level information,such as GIS layers – a primary reason why this screening step is performed for aconstrained set of assets. This is in part because the lifespan of assets is typicallyfluid, depending greatly on changing external conditions (of which climate isone, usage another) and on intermediate treatments (asset management), whichcan shorten or extend lifespan significantly. Estimates of asset design life may bemore readily obtained from asset management databases, where available.Particularly for assets expected to perform over very long time spans – up to acentury or more for some bridges – lifespan might be determined by applyingcommon design life rules of thumb to actual construction dates 24 . The managersof these assets should play a key role in formulating these estimates. As with allprojections considered in the assessment, estimates of asset lifespan need not beperfect, just feasible based on the best currently available information.23 Subject to the erosion of fill beneath piers and/or abutments, creating structural andsafety risks.24 See, for example: M. Meyer, 2012, Design Standards for U.S. Transportation Infrastructure:The Implications of Climate Change. Developed as a working paper for NCHRP 20-83(5).12-4 Cambridge Systematics, Inc.