Whistle posts were positioned at approaches to grade crossing intersections to order the locomotive engineer to sound his whistle as a warning. These posts were positioned one quarter mile before the crossings and on the right side of the track to be visible to the engineer. At a typical speed of 30 miles per hour, a train would take 30 seconds to travel the distance from the whistle post to the crossing.

The warning signal for a crossing was a series of four whistle blasts: long-long-short-long. Many of us of a certain age will recognize that signal, having heard it so often as youngsters. The engineer was required to extend this four-blast signal until the locomotive had occupied the intersection.

There is an interesting story about the origin of this crossing signal. In Morse code, this sequence of long-long-short-long is the letter “Q.” The story states that it dates back to the days of the Queen of England. When she would return to harbor aboard a ship, that ship would blast the letter “Q” with their horn to let everyone know that the Queen of England was aboard and to yield the right of way to it.

The following whistle posts have been restored to date along the Northern Line:

Bullock’s Crossing Road, southbound
Prescott Hill Road, northbound
Sargent Hill Road, northbound and southbound
Danbury Center, southbound
Jack Wells Road, northbound
Channel Road, southbound
Sam Hill Road, northbound and southbound
Dyer’s Crossing, northbound
Carr Street, northbound and southbound
Kimble Street, northbound and southbound
Holy Cross Road, northbound