BRAKING CURVES.

Figure 2.

This diagram shows the distance in feet required upon a straight and level track to bring a train to rest from different initial speeds in miles per hour and at various rates of deceleration. For instance, to stop a train from 26 miles an hour in 26 seconds or at the uniform rate of retardation of one mile per hour per second will require 500 feet, whereas to stop this same train in 13 seconds or at the rate of 2 miles per hour per second will require but 250 feet. The dotted lines indicate the curve of braking distance which was used in laying out the Subway signal system and it will be seen that this curve, constructed from test data, corresponds very nearly to the theoretical curve of 2 miles per hour per second. The fact that with improved brakes it is possible to stop a train at the rate of 21⁄2 miles per hour per second or greater suggests that possibly the braking distance-and therefore the lengths of the blocks and the headway-can be correspondingly reduced.

COMPARATIVE DECELERATION CURVES.

FIGURE 3.

This diagram shows the number of seconds required to stop a train at various rates of deceleration. The length of an express station platform is 350 feet. If the head end of a train coming to a stop at this platform runs the length of the platform in 151⁄2 seconds the train is braking at an average of 2 miles per hour per second. If, however, the time to run the length of the platform is 22 seconds, then the rate of retardation or braking is an average of but one mile per hour per second.

The shaded portion of the diagram covers points of observation which were made on a great many trains and indicate that the braking practice in the present Subway is varying through wide limits. In bringing a train to a rest at the station platform, many motormen take at least 5 seconds longer than other or more skilled motormen. The single curve indicating a stop in the length of the platform of 14 seconds is the result of one observation in which an exceptionally quick stop was made but this stop shows the possibilities of eventual improvement.

TIME REQUIRED TO STOP TRAINS.

Figure 4.

In this diagram Curve A shows a train reaching the platform at a speed of 22 miles an hour and stopping in 22 seconds or at the rate of one mile per hour per second. Curve B shows the train stopping in 151⁄2 seconds from a speed of 31 miles per hour or a deceleration rate of 2 miles per hour per second. Curve C shows the first train which reached the platform at 22 miles per hour-accelerating first to about 24 miles per hour and then decelerating at the rate of 2 miles per hour per second thus coming to a stop in 161⁄2 seconds instead of 22 seconds. This latter curve shows the method of stopping which should be followed by all trains. An indicator should be located 100 feet from the entering end of the platform and the motormen should be trained and instructed to reach this indicator with their trains running at a predetermined speed. The motormen become sufficiently expert in judging the speed of the train to make this rule practicable and it can be carried out without the use of speed indicators in the motorman's cab.

A strict adherence to this rule would reduce the operating headway of the present Subway by at least 5 seconds and there is no other improvement possible which will add so much to the capacity of the Subway in proportion to the amount of investment involved: