Disaggregating Variability in Projected Benefits of Transit State of Good Repair Due to Uncertainty of Travel Demand Forecasts

Abstract

Maintaining transit infrastructure in a state of good repair (SGR) is key to improving the sustainability of urban transportation. Insufficient SGR investments lead to the deterioration of transit agency assets and to declining service quality and a loss of ridership. Thus, a significant portion of the benefits of SGR investments are due to travel demand impacts, but the literature on this subject is extremely sparse. As a result, evidence and demand modeling tools to properly determine benefits of transit SGR investments are lacking. This paper quantifies the impact that this gap of knowledge has on SGR investment benefit forecasts. It presents a comprehensive sensitivity analysis to determine first-order and higher-order effects of travel demand variables on the variance in SGR benefit estimates, using 37 hypothetical investment scenarios. The results show that the variance attributable to uncertainty in travel demand forecasts is considerable and may skew investment decisions. It varies by SGR project type and may be reduced by addressing some of the variables with which travel demand forecasts interact.