Guide for the Preservation of Highway Tunnel Systems (2015) / Chapter Skim
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From page 18... ...
18 C H A P T E R 5 5.1 Evaluating Alternative Preservation Actions To evaluate the effectiveness of a proposed tunnel preservation action, several factors must be considered. First, what effect does the improvement have on achieving the agency's overall goals and objectives (i.e., meeting their LOSs)
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From page 19... ...
Measuring Effectiveness of Preservation Actions 19 The 2011 AASHTO Transportation Asset Management Guide provides an approach for risk assessment where the following are evaluated: • Likelihood of an extreme event, such as a flood, earthquake, asset failure, or other risk driver, expressed as a probability, or range of probability, of an event. • Consequences to the asset, a categorization of the damage or loss of function of the asset, and conditions on occurrence of an event.
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20 Guide for the Preservation of Highway Tunnel Systems within the agency than others. For example, safety and preservation are two goals that typically rank higher than other LOSs for most highway agencies.
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Measuring Effectiveness of Preservation Actions 21 spills within the tunnel to local streams, exhausting of tunnel emissions in an urban area with air-rights structures, or disposal of tunnel lights containing hazardous materials; however, the agency deemed the likelihood of these kinds of issues in its tunnels to be low. This iterative process for consideration of ranking should continue within the AAMT until all members are in agreement with the ranking of LOS elements in order of importance.
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22 Guide for the Preservation of Highway Tunnel Systems LOS Reliability Safety Security Preservation Quality ofService Environment Weights 20% 40% 5% 18% 15% 2% Preservation Action Tunnel # Ventilation upgrade to meet NFPA 502 1 1 5 1 5 1 N/A Install new LED lights 1 3 4 2 5 4 5 CO system – repair to operating condition 2 2 5 N/A 4 N/A 2 Repair active leak in tunnel 4 4 5 N/A 5 5 N/A Remove existing concrete tunnel ceiling 6 4 5 N/A 4 5 N/A Install flood gates 6 4 4 N/A 5 N/A N/A Table 5-3. Level-of-service ratings for selected preservation actions.
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Measuring Effectiveness of Preservation Actions 23 environment is a 5. Although the current system provides the needed lighting levels to operate the tunnel, a failure could require tunnel closure, so reliability is assigned a 3.
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24 Guide for the Preservation of Highway Tunnel Systems where LOS = agency level-of-service score, R = reliability rating, Sa = safety rating, Se = security rating, P = preservation rating, Q = quality of service rating, E = environment rating, and WR, WSa, WSe, WP, WQ, WE = weights for reliability, safety, security, preservation, quality of service, and environment scores, where (WR + WSa + WSe + WP + WQ + WE)
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From page 25... ...
Measuring Effectiveness of Preservation Actions 25 affect the resulting LOS score and, therefore, should be established by the AAMT and used consistently. As indicated in Section 5.1, the AAMT should follow a process where the LOSs are prioritized, and then individual weights are applied to each.
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From page 26... ...
26 Guide for the Preservation of Highway Tunnel Systems when evaluating alternative approaches, whether alternative equipment or varying options for rehabilitation, to ensure the greatest cost efficiency over the life of the tunnel. This process involves evaluating the alternatives over a given duration or economic life to determine specific costs involved for each option and then equating them through a series of mathematical formulas that enable the costs of each option to be compared at a common point in time.
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Measuring Effectiveness of Preservation Actions 27 where P = present worth, F = future one-time expense, n = number of years, and i = discount rate. Future expenses can also be uniform, in that the same expense occurs at the end of each year.
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28 Guide for the Preservation of Highway Tunnel Systems factors are also unique to the desired result. The procedure for using standard economic tables is as follows: • Determine the discount rate (i)
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Measuring Effectiveness of Preservation Actions 29 5.3.1.3 Discount Rate Caution should be taken when determining the appropriate discount rate. Because of the power of compounded interest, a difference in discount rate can actually change the final outcome of the analysis if the repair/rehabilitation options being considered have different arrangements of uniform and one-time costs.
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30 Guide for the Preservation of Highway Tunnel Systems Pr es er va tio n A ct io n Tu nn el # C ap ita l C os t ( $)
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Measuring Effectiveness of Preservation Actions 31 Tunnel 2 for a given preservation action focused on improving safety if it is not implemented than for the lower-ADT Tunnel 1. The impact of having to close the tunnel would be greater for Tunnel 2 than Tunnel 1 due to the higher number of users.
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32 Guide for the Preservation of Highway Tunnel Systems where CE = cost-effectiveness score, ADT = average daily traffic, number of vehicles, ALCC/ADT = annual life-cycle cost per daily vehicle, and F = cost factor, varies (see Section 5.3.4)
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From page 33... ...
Measuring Effectiveness of Preservation Actions 33 condition or a condition requiring closure of the tunnel. There are several factors that contribute to urgency: condition, remaining life, regulatory requirements, and unplanned events.
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34 Guide for the Preservation of Highway Tunnel Systems needed improvements. Such conditions can be established by following the guidelines of the FHWA 2015 Specifications for National Tunnel Inventory.
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Measuring Effectiveness of Preservation Actions 35 risk of these events and their possible impacts and plan for these occurrences. Preservation actions focused on resiliency may be difficult to prioritize because the future is unknown, but owners must evaluate the risks and consider these risks as another factor when developing the RBU score.
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36 Guide for the Preservation of Highway Tunnel Systems A selection of Agency X's RBU ratings is provided in Table 5-9; additional preservation actions are presented in Appendix D The rationale for assigning each of the RBU ratings is explained in the following.
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Measuring Effectiveness of Preservation Actions 37 5.4.6 Calibrating the Risk-Based Urgency Score There is considerable subjectivity in the determination of the RBU score. In addition, the scores are further aggregated by the multiplication factor of 10.
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38 Guide for the Preservation of Highway Tunnel Systems considering the final measure of effectiveness score (Section 5.5; RBU score assigned a weight of 45% of total combined score)
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From page 39... ...
Measuring Effectiveness of Preservation Actions 39 Measure of effectiveness is computed as follows: MOE score LOS CE RBU Equation 5-7LOS CE RBUW W W= ∗ + ∗ + ∗ where LOS = level-of-service score, CE = cost-effectiveness score, RBU = risk-based urgency score, and WLOS, WCE, WRBU = weights for the LOS, CE, and RBU, where (WLOS + WCE + WRBU)
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