What does moving the automatic brake valve handle into the service zone reduce?

Moving the automatic brake valve handle into the service zone reduces equalizing reservoir pressure. The equalizing reservoir, which helps control the brake system, maintains a certain pressure that is crucial for proper brake function. When the brake valve handle is moved into the service position, it allows brake pipe air to flow into the equalizing reservoir, resulting in a pressure drop in that reservoir. This action is an integral part of the braking process, as it enables the train to decelerate by controlling the amount of air pressure distributed to the brake cylinders of the cars.

In contrast, the other options focus on different aspects of the braking system. Brake cylinder air pressure relates to the force applied at the wheels, auxiliary reservoir air pertains to stored air for car brake operation, and service reservoir pressure involves the larger system of air storage for braking functions. While each of these elements plays a role in the overall operation of the air brake system, the primary effect of moving the valve handle into the service zone specifically targets the equalizing reservoir pressure.