. Proposed electrification of the Milwaukee branch, Chicago & Northwestern railway. f Technology. No attempt has been made to enter into thedetails of all or any particular portion of thedesign. Such a task as a detail design couldonly be accomplished by a Board of Engineers withat least two or three years time to devote tothe subject. THE SPEED TIME CURVE. In the preliminary calculation and deter-mination of the speed-time curve the followingfactors have been considered: (a) Choice of acceleration, involvingdistance between stops, the average speed,and weight of car. (b) The profile of the li
. Proposed electrification of the Milwaukee branch, Chicago & Northwestern railway. f Technology. No attempt has been made to enter into thedetails of all or any particular portion of thedesign. Such a task as a detail design couldonly be accomplished by a Board of Engineers withat least two or three years time to devote tothe subject. THE SPEED TIME CURVE. In the preliminary calculation and deter-mination of the speed-time curve the followingfactors have been considered: (a) Choice of acceleration, involvingdistance between stops, the average speed,and weight of car. (b) The profile of the line. (c) Choice of motor and gear ratio. (d) Frequency of the service. Choice of Acceleration. The general solution of the problem is hereconsidered because of its important relation tothe choice of motors, a factor which directlydetermines the initial cost of the entire system. Referring to Fig. 1, an arbitrarily assumedstraight line speed-time curve for a straightand level track, the following notation has beenused: a - Acceleration in miles per hour persecond along OA (sDA+OD). b - Retardation during braking (-AbtEB)c - Retardation during coasting(=BE*EC)x - Time required to go from C to A.(zOD)y - Time for AB (=DE)z - Time for EC (=EC)? ?i- Distance for OA. (=Area OAD)s2- Distance for AB. (=Area DABE)8 - Distance for BG. (=Area EBG)T - Total time of run. (=0C)L - Total distance. (=Area OABC)V - Average velocity. ( LVT) ( onemile per hour - feet per second) As indicated in the figure the car is assumedto be moving with a constant acceleration up toits maximum speed for a time 0D, then is retardedat a constant coasting rate for a time DE, andfinally is retarded during braking at a constantacceleration over a period of time equal to EG. The velocities, times, and distances referredto in the foregoing discussion may be representedby the three following equations: (1) ax - by - cz - 0 (2) x -f- y -f- z = T (3) ax2 - by2+cz2-v- 2axy = : A __ t . ^ . ^ Then
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