Lifecycle Design and Cumulative Benefit-Cost Analysis for Transportation Resiliency
Posted: December 7, 2016 at 10:04 am, Last Updated: December 7, 2016 at 10:05 am
For roads, bridges, and culverts it is challenging to make design decisions that anticipate a range of possible environmental futures. Not having a crystal ball, planners and engineers generally must select, for example, a bridge height without having a clear estimate of whether they will be over- or underbuilding for future hydrologic conditions. In so doing, the odds of selecting the most robust and most financially efficient design, given life cycle costs of the asset, are unknown and small in any case. The central problem is that most design methods that attempt to plan for extreme weather events do so via snapshots—e.g. planning for the 100-year storm—but this fails to account for benefits of cumulative avoided damages from extreme events, especially given that other base conditions such as sea levels in coastal areas and probabilities of extreme events themselves are also changing over time. That is, by not operating cumulatively, both the numerator and denominator in many benefit-cost evaluations may be inaccurate.
Lifecycle design based on cumulative business case analysis (BCA) could help address these issues. It encompasses the range of possible extreme weather events that may occur during the useful life of the asset. Asset damage and maintenance costs are tallied through use of depth-damage functions tailored to each candidate structure. Probabilities of weather events of different intensities are incorporated into models that subject the assets to changing conditions over time. When conducted at the correct points in an ongoing asset management program, the approach identifies which candidate design is the best investment to mitigate risks from a changing climate. When additionally integrated with asset ranking based on organizational risk, resources can be focused on solely those assets ranked 1) most sensitive and critical in the face of the environmental threats and 2) most likely to cause bureaucratic and other delays (e.g., NEPA documentation and regulatory review). Efforts of this type create opportunity to enhance ongoing asset management procedures by providing common language and reference points about moving toward resilient design, across divisions within a transportation organization.
Recent examples illustrate these points. Under a Federal Highway pilot project with the Maine Department of Transportation for vulnerable bridges and culverts in three towns, alternative engineering designs were created that would be expected to be resilient to 3.3’ and 6’ of sea level rise. Depth damage functions were created for these designs and for the existing structures. Relative cost-efficiency of the designs was evaluated in each location under a range of sea level rise and storm surge scenarios, cumulatively over time—comparing results for each design to replacing each asset to today’s design standards. Results showed which candidate structures were the best investments given a range of future scenarios and facilitated significant organizational shifts toward resiliency-based programming. Sample life-cycle cost data are provided below for one of the sites. Importantly, the most efficient designs were different not just between sea-level rise scenarios, but also between nearby locations— emphasizing that analysis of this type needs to be site-specific to encompass variability from local tidal regimes, depth damage functions, and hydrologic idiosyncrasies.
|Low Sea Level Rise (3.3′)|
Costs by 2100
|LIFE CYCLE COST BY 2100|
|Replace in Kind||$400,000||$697,476||$1,097,476|
|Replace with 3.3′ SLR design||$594,000||$697,476||$1,291,476|
|Replace with 6′ SLR design||$1,000,000||$281,242||$1,281,242|
|High Sea Level Rise (6′)|
Costs by 2100
|LIFE CYCLE COST BY 2100|
|Replace in Kind||$400,000||$1,867,580||$2,267,580|
|Replace with 3.3′ SLR design||$594,000||$1,867,580||$2,461,580|
|Replace with 6′ SLR design||$1,000,000||$916,598||$1,916,598|
Under a second Federal Highway pilot with the Minnesota Department of Transportation, benefit-cost analyses were conducted for large culverts (28’ triple-box) in two locations expected to experience significantly increased rainfall in the coming decades. Depth damage functions were created for these designs and the existing structures. Relative cost-efficiency of the designs was evaluated under a range of rainfall and runoff scenarios, comparing results to replacing each asset to today’s design standards. Results showed which candidate structures were the best investment given a range of scenarios and considering both structural repair costs and non-local, non-structural costs (e.g., social costs from detours and injuries).
In a third project (for Federal Highway’s SHRP2 EcoLogical program and through Maine Department of Transportation), inland culverts were prioritized for how much risk they represented to the agency. The six highest ranked assets were then analyzed using burdened and unburdened depth damage functions as above. Additional analytic steps helped evaluate cumulative life-cycle costs across runoff scenarios as in the “heat maps” below, where scenarios are on the x-axis and candidate designs are on the y-axis. Results indicate the least expensive design is the most financially robust; but again this depends on local conditions and requires site-specific analysis.
The essence of these approaches is the powerful “what if” question. With the culvert on the left, if we design for the Q25 storm (“25-year storm”) it is likely to be robust across future runoff scenarios, in terms of total expenses to the organization—whereas with the culvert on the right, the Q100 design is more appropriate because it would be undesirable to build the Q25 design and end up with a high runoff future. These are in contrast to the larger designs in the top two rows, which would clearly represent overbuilding, in any envisioned hydraulic future. This type of analysis utilizes the inherent flexibility of the conceptual design stage to identify no-regrets design thresholds where costs to the organization are minimized across potential futures. It also avoids crossing the preliminary design threshold too early, when constraints of permitting, regulation, politics, and environmental issues make it too late to ask “what if” we had designed another way.
The need for this type of bottom-up analysis has been emphasized in recent transportation engineering literature. Challenges in incorporating it more broadly have included not only the absence of robust methods to conduct the work but also identified means for transportation organizations to undertake it in a cost-effective manner that can scale up across hundreds of assets in need of repair or replacement. Current efforts are thus organized around low cost-per-unit analytic frameworks that can expand to become part of regular operations.
And importantly, “scenario-based life-cycle costing” of this type should help transportation organizations evolve their asset management and prioritization process in a diversity of landscape contexts. Explorations of how this works in practice are currently underway at the Maine Department of Transportation. For example, an automatic flagging process is being structured whereby bridges, roads, culverts, and multimodal facilities throughout coastal Maine that come up for repair or replacement in a normal triennial structural review calendar are subjected to spatial overlays of possible future flooding by the 100-year storm and by low- and high-sea level rise scenarios. Assets are then automatically flagged in various databases according to how many of the polygons they intersect.
These flag references are not just being made available to Environmental and Planning Divisions, but are also becoming part of common vocabulary and use in Engineering, Operations, and Maintenance during the normal structural review calendar. Via internal communication vehicles of this type, assets most vulnerable to changing hydrologic patterns each year are more likely to receive lifecycle BCA at the conceptual design stage as above.
The methods are an important element of a swiftly evolving discipline, developing in parallel with a range of other efforts such as the Transportation Research Board’s current NCHRP 15-61 on “Applying climate change information to hydraulic and hydrologic design of transportation infrastructure.” They are also a substantive contribution to major national policy and agency initiatives, including the Moving Ahead for Progress in the 21st Century (MAP-21) and Executive Order 13604: Improving Performance of Federal Permitting and Review of Infrastructure Projects. Further, they address a critical issue for benefit-cost analysis more broadly, that many of the fundamental tenets it represents are coming under scrutiny and the limits of its practical and methodological boundaries are being tested. Their implementation ensures that the least expensive but also resilient design is selected, likely saving transportation organizations significant funds in construction and over time.
However, of course design decisions for transportation upgrades need to encompass more than just financial implications. They also need to reflect non-local and systemic questions about social, environmental, and economic implications of candidate designs. To some extent these issues can be integrated into the benefit-cost methods summarized here, accounting for non-structural benefits and costs of designs under consideration; exploration of these approaches is underway. However this needs to also occur in tandem with other ranking and screening methods, to reflect the broadest possible range of agency concerns. In this manner these methods become not a major paradigm shift but simply an enhancement to an overall set of tools to make better choices on behalf of our evolving transportation network.
Dr. Merrill is a Senior Practice Leader with GEI Consultants. From 2001 – 2012 he was Associate Research Professor at the Muskie School of Public Service, University of Southern Maine, and Director of US EPA’s New England Environmental Finance Center. He has held directorships in nonprofit, academic, private, and government sectors. He has published over 20 peer-reviewed articles and received many awards for his work – including a military medal for distinguished public service in the year 2000.
Judy has directed Maine DOT’s Environmental Office since 2006, leading work on extreme weather and climate resiliency, landscape-level analysis, and streamlining environmental processes. Before this she worked seven years with the Maine Department of Environmental Protection and three years with the Maine Department of Agriculture. She has a B.S. from West Virginia University, two M.S. degrees from the University of Maine at Orono, and is ABD in the Ph.D. program at the Edmund S. Muskie School of Public Service.
 Sam Merrill & Judy Gates, Integrating Storm Surge and Sea Level Rise Vulnerability Assessments and Criticality Analyses into Asset Management at MaineDOT (Maine: Catalysis Adaptation Partners & Maine Department of Transportation, 2014) (sponsored by the Federal Highway Administration), http://www.fhwa.dot.gov/environment/climate_change/adaptation/resilience_pilots/2013-2015_pilots/maine/final_report/maine.pdf.
 Minnesota Department of Transportation, MnDOT Flash Flood Vulnerability and Adaptation Assessment Pilot Project: Final Report, (St. Paul, Minnesota; Minnesota Department of Transportation, 2014), http://www.fhwa.dot.gov/environment/climate_change/adaptation/resilience_pilots/2013-2015_pilots/minnesota/final_report/mndotreport.pdf.
 Maine Department of Transportation, Assessing Program Risk through Benefit-Cost Analysis for Bridge and Culvert Design: Final Report (Augusta, Maine; Maine Department of Transportation, 2015): 24.
 See, e.g., Qing-Chang Lu, et al., “Economic Analyses of Sea-Level Rise Adaptation Strategies in Transportation Considering Spatial Autocorrelation,” Transportation Research Part D 33 (2014): 87-94, http://ac.els-cdn.com/S1361920914001308/1-s2.0-S1361920914001308-main.pdf?_tid=4139e454-ab5e-11e6-b244-00000aab0f27&acdnat=1479233379_a4f59b53d668a27c98d10e1a02d4b09e.
 See “Applying Climate Change Information to Hydrologic and Hydraulic Design of Transportation Infrastructure,” The National Academies of Sciences, Engineering, and Medicine, http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4046.
 See “MAP-21 – Moving Ahead for Progress in the 21st Century Act,” Federal Motor Carrier Safety Administration, updated Feb. 18, 2016, https://www.fmcsa.dot.gov/mission/policy/map-21-moving-ahead-progress-21st-century-act.
 Exec. Order No. 13604, 77 F.R. 18887 (2012), https://www.gpo.gov/fdsys/pkg/FR-2012-03-28/pdf/2012-7636.pdf.
 Fran Sussman, et al., “Introduction to a Special Issue Entitled: Perspectives on Implementing Benefit-Cost Assessment in Climate Assessment,” Journal of Benefit-Cost Analysis 5, no. 3 (2014): 333-46, https://www.degruyter.com/view/j/jbca.2014.5.issue-3/issue-files/jbca.2014.5.issue-3.xml.
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