1 ABSTRACT: Recent events have created renewed interest in deploying automatic linebreak control valves across the nation's natural gas pipeline infrastructure. However, certain pipeline configurations may not lend themselves to the installation of these devices. One such area on the Southern California Gas Company (SoCalGas) and San Diego Gas & Electric Company (SDG&E) system is the "Rainbow Corridor". The Rainbow Corridor is an area in southern Riverside County, California, where a series of three parallel pipelines of differing diameters provide the majority of gas supply to San Diego County. SoCalGas and SDG&E use transient hydraulic software to evaluate proper settings for proposed automatic linebreak control valves. During pipeline break conditions, a large pressure drop and corresponding pressure rate of change is observed at the valve location. This pressure rate of drop (ROD) is measured over a period of time and is used by the control valve to determine if a line rupture has occurred. Breaks are simulated at the furthest point from the valve on the line, or in between other control valves, in order to catch a break anywhere on the pipeline. Normal operating procedures, including operation of compressor stations, power plants, valves, etc., have the same effect on the valve, typically to a lesser extent. This unique problem is magnified by the differing pipeline diameters in the Rainbow Corridor, where a break on a large line has a drastic effect on a smaller diameter pipeline. The case study demonstrates that there are certain special circumstances where automatic linebreak control valves will be more of a hindrance than helpful, and would be better suited with remote control operation. Careful modeling of the pipeline network produced a plan which mitigated the likelihood of losing all supply to San Diego County, while improving the safety of the SoCalGas/SDG&E pipeline network.