An adapter is designed to interconnect the two glad hands that extend from the adjacently disposed ends of a pair of rail vehicles in a train. The housing of the adapter includes first and second connector bodies and an intermediate portion situated between the two connector bodies. The adapter housing encloses a flow chamber that runs from the first connector body through the intermediate portion to the second connector body. The intermediate portion defines a vertically disposed access port in communication with the flow chamber of the adapter housing. The connector bodies are formed on opposite, vertically oriented sides of the adapter housing. Each connector body features a mating surface from which a flow port in communication with the flow chamber emerges. Each connector body also includes a mechanism that allows the connector body to mechanically couple to one of the glad hands. When so coupled, the mating surface of the connector body is aligned with the mating surface of its corresponding glad hand with a sealing member of the glad hand held in compression therebetween. By coupling the glad hands to connector bodies of the adapter, a leak proof passage is provided from one glad hand through the flow chamber and the flow ports of the adapter housing to the other glad hand. It is directly to the access port or indirectly via a fitting that an external device can connect for the purpose of affecting the pressure contained by the brake pipe of the train.