Comparing the utility of decision trees and support vector machines when planning inspections of linear sewer infrastructure

Closed-circuit television inspection technology is traditionally used to identify aging sewer pipes requiring rehabilitation. While these inspections provide essential information on the condition of pipes hidden from day-to-day view, they are expensive and often limited to small portions of an entire sewer system. Municipalities may benefit from utilizing predictive analytics to leverage existing inspection datasets so that reliable predictions of condition are available for pipes that have not yet been inspected. The predictive capabilities of data mining systems, namely support vector machines (SVMs) and decision tree classifiers, are demonstrated using a case study of sanitary sewer pipe inspection data collected by the municipality of Guelph, Ontario, Canada. The modeling algorithms are implemented using open-source software and are tuned to counteract the negative impact on predictive performance resulting from class imbalance common within pipe inspection datasets. The decision tree classifier outperforms SVM for this classification task – achieving an acceptable area under the receiver operating characteristic curve of 0.77 and an overall accuracy of 76% on a stratified test set. Although predicting individual pipe condition is a notoriously difficult task, decision trees are found to be a useful screening tool for planning future inspection-related activities.