What is the result of opening the trip cock on a subway car?

Opening the trip cock on a subway car activates the emergency brake system of the train. This mechanism is a safety feature designed to bring the train to an immediate stop in the event of an emergency or if there is a breach in protocol. When the trip cock is opened, it effectively signals the train's braking system to engage, providing a rapid response to potential hazards or unsafe conditions on the tracks.

This safety protocol is crucial in maintaining the safety of the passengers and crew onboard, as it ensures that the train can stop quickly and prevent accidents or injuries. The design and purpose of the trip cock highlight its importance in emergency situations, allowing operators to respond to critical events efficiently.

While other options may touch on different facets of train operations, such as gradual stopping or automatic door operation, they do not pertain to the specific function of the trip cock, which is solely to invoke the emergency braking system when activated.