Crash modification factor (CMF) provides the expected change in crash frequency due to the implementation of a countermeasure or a change in a particular site condition. State and local transportation agencies determine CMF values by utilizing the Highway Safety Manual (HSM). The HSM provides CMF values for various types of facilities and treatments. However, the HSM’s coverage of work zone-related CMF values is limited. This report introduces practitioners to: the procedure for evaluating work zone countermeasures using existing CMFs and the procedures for developing new work zone CMFs. Once derived, CMFs can be used for selecting countermeasures and scheduling lane closures.