Tunnels are defined as enclosed roadways with vehicle access that is restricted to portals, regardless of type of structure or method of construction. Tunnels do not include highway bridges, railroad bridges, or other bridges over a roadway. Tunnels are structures that require special design considerations that may include lighting, ventilation, fire protection systems, and emergency egress capacity based on the owner’s determination. Tunnel preservation includes actions or strategies that prevent, delay, or reduce deterioration of tunnel systems (preventive maintenance); restore the function of existing tunnels (repair or rehabilitation); and keep tunnels in good condition and extend their useful life. Every year, significant public funds are needed to inspect and maintain tunnels that were not designed to be easily inspected and maintained. Nevertheless, well-planned preventive maintenance is a cost-effective strategy to keep tunnels safe and operational. Practitioners often apply preservation strategies on the basis of judgment or common sense using available resources. However, it is difficult to translate these strategies into coherent and convincing arguments that will lead to support for aggressive and well-planned programs of highway tunnel preservation. Also, tunnels are complex structures that include mechanical, electrical, life safety, and structural systems. Deciding the priorities among these disparate elements can be very difficult. Therefore, tunnel programs may be inadequately funded due to absence of a credible, quantitative basis for measuring effectiveness. Research was performed under NCHRP Project 14-27 by Gannett Fleming, Inc., to develop a guide for possible adoption by AASHTO that will (1) assemble a catalog of highway tunnel preservation actions, (2) quantify the benefits of tunnel preservation actions, (3) provide decision-making tools to optimize tunnel preservation actions, and (4) develop a method to determine appropriate levels of funding and staffing to achieve agency-selected goals and performance measures. The research agency’s final report that documents the entire research effort is available on the NCHRP 14-27 project description page on the TRB website. This report presents a guide for the preservation of highway tunnel systems to (1) assist tunnel owners in making informed decisions using an asset management process to support their prioritization of highway tunnel preservation actions and (2) provide executives with credible, evidence-based information on capital funding needs for tunnel improvements as part of their overall transportation system funding, as well as a means for communicating those needs. This guide provides a process for prioritizing needs, using an overall measure of effectiveness that is calculated using a risk-based urgency score, and developing capital funding and staffing programs to accomplish tunnel preservation goals, and also serves as a training tool for new personnel. The material in this report will be of immediate interest to tunnel owners and operators. (Author/publisher)
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