With the rapid expansion of Intelligent Transportation Systems (ITS) for traffic management, the cyber-physical security of smart transportation infrastructures is becoming increasingly crucial. This paper investigates the impact of intentional disruptions on variable speed limit (VSL) signs within traffic networks. We present a threat model to identify vulnerabilities in the VSL communication network and potential access points for attackers. An analytical accident model was developed, and various disruption scenarios were simulated using a case study of Highway 1 in British Columbia, Canada, in SUMO (Simulation of Urban MObility) to assess the potential for crashes and safety issues resulting from VSL disruptions. Surrogate Safety Measures (SSM) were employed as key measures of safety concerns. Our findings highlight notable risks, including up to 56$\%$ additional conflicts, posed by these intentional disruptions. Various mitigation strategies are proposed to enhance traffic safety and resilience against VSL manipulation.