Modeling cost and time uncertainty in rail line construction

Abstract

Transportation construction projects are often plagued by cost overruns and delays. Technical, economic-political, psychological, and legal causes explain the frequent underestimations. To counteract such underestimations, the author developed an innovative approach to capture cost and time uncertainty in rail line projects, and applied this to the construction of a new high speed rail line in Portugal. The construction of the four main types of structures in rail lines (tunnels, viaducts, cuts and embankments) is modeled bottom-up from the single activity to the entire rail line. Sub-networks of activities are combined in structure networks to model the rail line structures; in turn, the structure networks are organized in the construction network to represent the rail line. For the first time, three sources of uncertainty (variability in the construction process, correlations between the costs of repeated activities, and disruptive events) are modeled jointly at the level of the single activity. These uncertainties are propagated to the total construction cost and time through the combination of the individual activity costs and times. The Construction and Uncertainty Models are integrated in the Decision Aids for Tunneling (DAT), which have been extended beyond tunneling to consider different structures and different uncertainty types. Based on historical input data and expert estimations, the cost and time uncertainty in the construction of four alignments of the new Portuguese high speed rail line is simulated. The three sources of uncertainty cause different cost and time impacts depending on the type of structure suggesting structure specific mitigation measures. Most importantly, their cumulative impact causes significant increases in construction cost and time compared to the deterministic estimates: 58% in the construction cost of tunnels, and 94% in the construction time of cuts and embankments. The Construction and Uncertainty Models and their integrated implementation in the DAT provide transportation agencies with a modeling tool to tackle cost and time uncertainty in the construction of rail lines and other linear/networked infrastructure projects.