Utility construction projects (UCP) are one-off endeavours with many unique characteristics, such as long period, complicated processes, abominable environment, financial intensity and dynamic organisation structures. Delays are common in the schedules of construction projects and cause significant losses to project parties. Therefore, it is important to quantify factors that cause delays and affect the execution phase of UCP in order to prevent potential delays and additional costs when managing the schedules. The purpose of this thesis is to quantify the critical factors that cause delays and affect the execution phase of UCP in the Netherlands using a Bayesian belief network (BBN). To fulfil this purpose, this thesis focuses on selecting the important critical factors that cause delays and affect the execution phase of UCP in the Netherlands, identifying the cause-effect relationships between the important critical factors and estimating the associated conditional probabilities. A total of 136 factors that influence construction projects have been collected through a literature review. With expert interviews, the factors that influence construction projects has been reduced to 59 critical factors that cause delays and affect the execution phase of UCP. These critical factors have been assessed by 138 respondents in questionnaire (I). In total twenty critical factors that cause delays and affect the execution phase of UCP in the Netherlands have been selected using the Fuzzy Delphi Method. Using nine Logical rules, a total of 56 cause-effect relationships between the selected critical factors have been accepted by forty respondents in questionnaire (II). Based on these cause-effect relationships a Directed graph (DG) has been developed. The knowledge and experience of ten experts have been used to create a BBN out of the DG by estimating the conditional probabilities in questionnaire (III). To identify and evaluate the probabilities of a factors’ condition on the basis of certain conditions of other factors, the BBN can be used. The most influential critical factors “Information delays and lack of information exchange between the parties”, “Incomplete and unclear drawings”, “Non-availability of drawing/design on time” and “Poor communication and coordination” need to be controlled in every UCP to avoid schedule delays in advance.