Guide for the Preservation of Highway Tunnel Systems (2015)

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14 4.1 Definitions of Preservation Actions Drawing on the definitions of preservation actions for bridges in the 2011 FHWA Bridge Preservation Guide,(4) the following definitions of preservation actions for tunnels are provided. Preservation actions include both preventive maintenance and rehabilitation activities. 4.1.1 Preventive Maintenance Preventive maintenance is a planned strategy of cost-effective treatments to an existing tunnel and its systems that preserves the systems, retards future deterioration, and maintains or improves the functional condition of the systems (without substantially increasing structural capacity). Preventive maintenance includes cyclical (non-condition-based) and condition-based activities. • Cyclical (non-condition-based) preventive maintenance: Activities performed at a pre- determined interval and aimed to preserve existing tunnel element or component conditions. Tunnel element or component conditions are not always directly improved as a result of these activities, but deterioration is expected to be delayed. Such maintenance is typically based on manufacturer recommendations, research recommendations, or a maintenance intervention strategy (e.g., light bulb replacement, vibration testing of fan motors, exercising of emergency generators). • Condition-based preventive maintenance: Activities that are performed on bridge elements as needed and identified through the tunnel inspection process. These activities are typically performed on a tunnel that is in overall good to fair condition to restore tunnel elements to a state of good repair. Similar to cyclical preventive maintenance activities, condition-based pre- ventive maintenance activities are designed to extend the useful life of tunnels. These may include emergency or other unscheduled, time-sensitive maintenance or observed repair activities. 4.1.2 Rehabilitation Rehabilitation involves major work required to restore the structural integrity of a tunnel or its systems, as well as work necessary to correct major safety defects. Rehabilitation could include structural repairs for capacity, operations, or safety improvements, as well as the addition of new tunnel systems as part of a fire and life safety assessment. 4.2 Establishing Preservation Actions Asset management of tunnels involves a continuous cycle of assessment, maintenance, and preservation over the life of the asset. Knowing what is needed in terms of preservation actions comes through assessment of the tunnel and its systems, which begins with regular inspections. C H A P T E R 4 Highway Tunnel Preservation Actions

Highway Tunnel Preservation Actions 15 With the promulgation of the anticipated National Tunnel Inspection Standards (NTIS), tunnels must be inspected every 2 years unless a risk assessment allows for this period to be extended. It is anticipated that many tunnel owners will use a reliability-based approach for tunnels, similar to that proposed for bridge inspection, per requirements of the NTIS. The reliability-based approach that was developed for bridge inspection(13) is equally appli- cable to tunnels and provides a process for evaluating tunnel inspection scope and frequencies. The process involves three simple steps that evaluate inspections in terms of the likelihood and extent of damage that could occur within a tunnel: • Step 1: Determine what can go wrong and how likely it is to occur. This step considers the likelihood of serious damage occurring and categorizes it within four occurrence factors ranging from remote (very unlikely) with a score of 1 to high (very likely) with a score of 4. • Step 2: Determine what the consequences are. This step assesses the consequences in terms of safety and serviceability, assuming the given damage modes occur. It categorizes the potential consequences into four consequence factors ranging from low (minor effect on serviceability) with a score of 1 through severe (e.g., collapse, loss of life) with a score of 4. • Step 3: Determine the inspection interval and scope. The occurrence factor and consequence factor are used to assess the inspection interval and the scope of the inspection, considering the potential damage modes that are likely to occur. The reliability matrix (Figure 4-1) illustrates that inspection intervals should be shorter if the occurrence and consequence factors are high and may be longer if the occurrence and consequence factors are low. During inspections, the inspection team notes and documents deficiencies. Recommendations for improvements to remedy deficiencies are typically developed as a part of the inspection process but may also be identified through normal operations. Specific preservation actions may be identified by tunnel operations personnel when a piece of equipment malfunctions; by specialty companies when providing troubleshooting and testing of equipment or systems; by agency/ consultant personnel after completion of walk-through, periodic, or in-depth inspections; and by the agency/consultant after performing code evaluations to identify actions needed to comply with current codes and standards. A code evaluation may trigger the need for installation of entirely new systems within the tunnel, such as life safety systems that are needed in the event of a fire. A complete list of preservation actions should be developed as part of an asset management process. Alternative preservation actions that might resolve a particular issue can be included and ultimately compared using the metric described in Chapter 5. The information critical for comparing preservation actions includes: • Tunnel identification, • Capital cost (the initial cost of the preservation action in present-value dollars; includes labor and equipment), • Annual change in cost (e.g., savings in energy or maintenance), • Average daily traffic, • Theoretical service life of the asset, • Remaining life of the asset prior to the preservation action being implemented, • Condition of the existing asset prior to the preservation action being implemented, • Whether the improvement is driven by a regulatory requirement or industry standard, and • Risk of unplanned events. Once this information has been established, the AAMT can use it to evaluate priorities based on element condition and associated risks of failure, can develop and consider various funding scenarios, and can forecast staffing needs as identified in Chapters 5, 6, and 7. Source: NCHRP Report 782: Proposed Guideline for Reliability-Based Bridge Inspection Practices. O cc ur re nc e Fa ct or Consequence Factor 1 1 2 2 3 Longer Shorter 3 4 4 Figure 4-1. Reliability matrix for determining maximum inspection intervals for bridges.

16 Guide for the Preservation of Highway Tunnel Systems 4.3 Examples of Tunnel Preservation Actions To assist tunnel owners in fully understanding typical preservation actions required for aging tunnel systems, this section summarizes some typical tunnel system conditions that, once identified, an owner needs to address. Consider an agency (“Agency X” used throughout this guide) with six tunnels with varying traffic volumes. Upon completion of its normal in-depth inspection of each tunnel, it was clear that improvements were needed. The structures ranged in structural condition from fair to poor, and the life safety and lighting systems were deemed obsolete by modern standards. The agency identified numerous preservation actions: • Making structural repairs of the tunnel walls, • Upgrading the electrical systems, • Replacing lighting systems, • Rehabilitating the existing mechanical systems (fans/motors/drives), • Cleaning and repairing all damper doors, • Adding a new fiber-optic system, • Installing CCTV cameras, • Evaluating and implementing flood protection measures, and • Overhauling the over-height truck detection system. Since major improvements were envisioned, the agency investigated possible improvements to upgrade life safety systems to comply with NFPA 502. These included: • Upgrades to the CO detection system, • Addition of a heat detection system for fire events, • Installing emergency signage providing distances to cross-passageways and exits, • Installing new call stations, • Providing alarms at all doors for security and detection at the operations center of security breaches, • Adding a dry standpipe system for fire, and • Potentially removing the tunnel ceiling to upgrade the ventilation system from semi-transverse to longitudinal ventilation. A summary of Agency X’s tunnels, including a tunnel identification number, ADT (in thousands), and a brief description, is provided in Table 4-1. A total of 32 preservation actions were identified based on the routine inspection of these six tunnels. To illustrate the range and nature of these actions, a selection of these preservation actions is presented in Table 4-2. For a complete list of all of Agency X’s preservation actions, refer to Appendix D. Additional examples of maintenance and preservation actions for numerous types of tunnel equipment are identified in Appendix B: Catalog of Preservation Actions. Tunnel # ADT (x1000) Description 1 40 Rural tunnel on a major Interstate 2 100 High-traffic urban tunnel downtown in a major city 3 30 Low-traffic urban tunnel outside of city 4 19 Very-low-traffic urban tunnel downtown 5 50 Moderately high-traffic tunnel near Tunnel 2 6 75 High-traffic urban tunnel accessing a major city in close proximity to the river Table 4-1. Agency X’s tunnels.

Highway Tunnel Preservation Actions 17 Preservation Action Tunnel # Ventilation upgrade to meet NFPA 502 1 Install new light-emitting diode (LED) lights 1 CO system – repair to operating condition 2 Repair active leak in tunnel 4 Remove existing concrete tunnel ceiling 6 Install flood gates 6 Table 4-2. Agency X’s preservation actions.