TRB's Transit Cooperative Research Program (TCRP) Research Report 198: The Relationship Between Transit Asset Condition and Service Quality documents the development of a quantitative method for characterizing service quality and demonstrates how this quantitative measure varies with changes in asset condition. It provides guidance on how asset condition and transit service quality relate in terms of investment prioritization.
Three Excel spreadsheets–a simplified Effective Journey Time (EJT) Calculator, a comprehensive EJT Calculator, and a worked example demonstrating the use of the comprehensive EJT Calculator—provide quantitative methods. Transit agencies may use this report and tools to better manage existing transit capital assets and make more efficient and effective investment decisions.
http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_rpt_198.zip

Infrastructure Assets: Transit Assets
Resource Types: Guide/Manual, Research Report
Capabilities: Tools & Technology
Management Processes: Performance Based Planning & Programming, Resource Allocation