Effective pipeline external corrosion control can be achieved by maintaining an adequate balance between the coating condition and the cathodic protection level. When a pipeline is in a corridor shared with parallel buried pipelines and high voltage alternating current (HVAC) power transmission lines, determining the adequacy of the cathodic protection (CP) system becomes a challenge. Misinterpretation of data being collected, or unreliable data can lead to the implementation of either ineffective or excessive mitigation programs for these pipelines. To obtain a better representation of the year-round performance of the CP system, additional testing to the conventional adjustive survey or close interval potential survey (CIPS or CIS) might be required on transmission pipelines collocated in HVAC corridors. The variation of the structure-to-electrolyte potential values over time and the effect of polarization cell replacement (PCR) units should be assessed when determining the level of polarization of the pipeline. Data from a case study is analyzed to illustrate additional testing procedures required to minimize the effects of HVAC systems when monitoring the CP level on transmission pipelines. The proper interpretation of the field monitoring data allows pipeline operators to develop and implement effective corrosion control mitigation plans.