addressing climate change adaptation in regional transportation plans

Addressing Climate Change Adaptation in Regional Transportation PlansA Guide for California MPOs and RTPAsIn some instances, multiple expected life spans might be associated with a singleasset, and multiple strategies – or a comprehensive strategy – may need to beemployed to mitigate impacts. For example, a given segment of roadway can bedivided into a series of components or elements with varying renewal cycles.The surface course (e.g., asphalt) might require replacement every 10 to 15 yearsdepending on usage, the base course every 30 years, and the right-of-way couldpersist indefinitely. If the stressor of concern is extreme temperatures leading tosurface course rutting, then it may be sufficient to monitor the condition andupgrade the asphalt binder (for instance) during normal repaving to increaseresiliency – an action of relatively low marginal costs and effort. If the stressor isroadway flooding, it may be necessary to raise the embankment and improvedrainage (such as the crown, side swales, and culverts) in conjunction withexpected reconstruction cycles – a costly procedure carried out at the most costefficientpoint in time. For severe flooding, if the only viable option is to modifythe right-of-way, funds could be sought for land acquisition and the existingsegment might be strategically abandoned by performing maintenance only forsafety purposes.Stressor Timeframe(s)Generally, stressor timeframes are established in Module 2b (ClimateInformation). However, a modest amount of additional work may be required inorder to better align the units of time pertaining to asset lifespan and stressortimeframes. Whereas asset lifespan may be measured in years (whenreplacements are planned or even budgeted) to decades, climate stressors areoften expressed in decadal or 30-year averages. To simplify matters, aligningstressors and assets by decade is recommended, and is an appropriate level ofgranularity for the assessment (a scale of years, in contrast, is too precise to berealistic, whereas 30-year spans are not sufficiently precise to base decisionmakingon). For example, if an asset were due for replacement in 2025, thiscould be reflected by assigning it to the 2020 to 2029 decade. Similarly, for astressor projection representing a 30-year average, the associated value could bedistributed evenly over a series of decades (e.g., 2020 to 2050). Especially if thefollowing 30-year span shows a notable increase, it may be appropriate toanecdotally indicate an upward trend, without representing an increase invalues.Applying the Climate Hazard Protection Windows will likely result in theremoval (or downgrade) of some asset/stressor combinations from furtherconsideration if the timing of hazards diminishes the prospect of exposure. Forasset/stressor combinations that remain, the Window will serve as a usefulframework for the time-sensitive consideration of adaptation strategies.Cambridge Systematics, Inc. 12-5