US1616554A - Transit system - Google Patents

Description

P. SACHS A TRANSIT sYsTEM Filed sem. s, 1923 3 Sheetssheetz Feb, 8 9 @2296 P. SACHSv TRANSIT SYSTEM Feb. 8, 1927,

' Filed sept. s, 1925 5 sheets-sheen HTTFVEYE Patented Feb. 8, 1927.

PHILLIP SACHS, OF NEW YORK. N. Y.

TRANSIT SYSTEM.

Application filed September 8, 1923.

This invention relates to an improved type and new method Of operating a rapid transit system.

The invention has for its object a solution of the rapid transit problem of cities, like New York for example, where economical utilization of the available space remaining for the construction of transit lines must be realized, togeth-er with increased carrying capacity. Although the invention is described with reference vto` the subways, the principlesof the invention are applicable wholly or in part to the elevated and surface railway systems.

It is an important object of this invention to provide a subway system and method of operation with greatly increased carrying capacity for the space required as compared with the present subways, and to provide a system which can be constructed and operated at less cost than subways of the existing type.

Another object is to provide a more flexible transit system, wherein the location of the stations can be readily and economically changed to accommodate the shifting vof the population and business centers. v

Another object is to provide a transit systeni in which the train length can be readilychanged without necessitating a change in the tracks, or the structure of the subway or the signal system.

Another object is to provide a subway, or other transit system, with a substantially uniform overall width whereby certain economies in construction and operation are realized.

Other objects of the invention are to reduce the train headway,.reduce power consumption and other operating expenses, increase the schedule speed, carrying capacity, operating efficiency and factor of safety, and eliminate or reduce stations and train congestion.

Various other objects and advantages will appear as the description of the invention proceeds.

. Referring now to the drawings which illustratc a preferred forni of the invention:

Figure l is a diagram illustra-ting the operation of the new system;v

Figure 2 is a diagrammatic plan view of the construction thereof, showing theL continuous island platform;

Serial No. 661,542.

Figure 3 is a diagrammatic plan view of a modified form of subway system;

Figure t is a cross sectional View of a subway such as is illustrated in Figure 2.y

vFigure 5 is across sectional view type of subway now in use. f

Figure 6 is side elevation illustrating one way of constructing the subway according to my invention.

Figure 7 is a diagrammatic view showing graphically the economical use of subsurface space. y

The urban transportation problem is rapidly gaining in seriousness and importance. On the one hand w-e are confronted with the rising ltendency in the cost of labor and materials entering into construction and equipment and operating expenses of the transit lines, which, in the face of the low fare that is generally demanded, makes the operation .thereof unprofitable and investment in new lines unattractive. On thel other hand our large cities are rapidly growing in population and expanding indu-strially and commercially and the riding habit of the inhabitants is as a result increasing, at the same time the motor traflic is also rapidly gaining, making walking unpleasant7 hazardous and slow. In other words, while the demand for rapidV 'transit is spreading and growing more urgent the task of meeting it i-s becoming more difficult. In New York city, for example, the situation is particularly serious for in addition to the huge sums of money that an adequate solution 'of the problem would call for, a shortage in underground street space is beginning to manifest itself. Already most of the longitudinal streets are provided with rapid transit lines. If the present rate of growth of traftic continues, a line under every longitudinal street will be inadequate in the course of about ten years. The building of additional subways of the present type would afford relief of only a temporary nature, but would at the'same time cause permanent harm, as it would tend to exhaust the citys finances, use up the citys streets, and burdenthe city with the payment of interest on an investment that according to present indications may never become self-supportino;

What we need then,- is not more subways,

but subways of a better type, subways that will cost less to construct, equip and opera-te CTI -fto suit Ian urban population.

soA

1....: v du than the present ones and provide a greater lrelating to the operation of the new system.

Uronsruotkon. The present rapid transit system .may be regarded as a compromise between the trolley and trunk line railroad. lhen the trolley became too slow, and its capacity too inadequate for the rapidly expanding, rapidly growing population, a rapid transit system was devised to operate on a private right of way,.and to stop at fixed points like a trunk line, but make these stops frequent enough In designing the structure for this system, however, two important points were either overlooked or vthought unnecessary to consider at that time:

Vhile the capacity of the trunk line is only limited by its train headway, the capacity of a rapid transit system is limited by yits train length which, in turn, is fixed Vby the length of station.

(2) lWhile in the case of the trunk line, new stations can be built and old ones removed or shifted to meet new conditions, in

the case of a rapid transit system, this can-A not readily be done.

The result has been a system sadly deticient in flexibility, elasticity and adaptabilityto new conditions, so essential to the success of any device providing transit for a rapidly growing city.

In order to meet the demands of the increasing population and shifting business and residential centers of our growiiig citp'ies, ya transit system should provide ready 'means for increasing its capacity by .increasing the train length and for relocating its stations as the business `and residential centers shift. The present subway system is deficient in these respects because the platforms are built to accommodate only a certain length of train, and each time a caris added to the train every platform on the line must be correspondingly lengthened, and in case the ytracks arecurved at the platform, as at island platforms, the tracks must also be' changed. To change the location of a station it is necessary to constructan entirely new'station with new loading platforms, new entrances, etc., and to destroy the old station, all -of which involves a great expense.v

nforder toovercome these andother objections and provide the desired flexibility,

I propose to construct a subway or other transit system with a continuous station platform for the entire length of the line whereby train lengths can be increased to an indefinite degree; and the stations or loading platforms, relocated or changed at will without expense.

An embodiment of this construction wherein the continuous platform is illustrated as being between the tracks, is shown diagrammatically in Figurev2, in which the numerals l 'to 24, etc. represent cross streets. r)The street C in which the subway is located is shown as `being wider than the cross streets to more clearly illustrate the construction of the subway, however, `the street C need not actually be any wider than the cross streets l to 24 etc. The continuous 'center platform -is designated bythe letter D, and itis subdivided by suitable markings such as lines 0l into the alternate stations A, A .and B, etc. rlhe :up (track t and down track t are located at.4 each side of the platform D and are substantially straight throughout their lengths.y Stairways d at frequent intervals, at and between stations, provide entrance and exit for the'y platform. It is at once apparent that with such a system no change in the platform is necessary when the trains are lengthened and that it is only necessary-to change the markings Z to relocate the stations. It will also be shown that track for track this construction will involve little or no additional expense, and when the capacity of the lines is compared will show a great economy over the present system.

ln the New York subways for example the local stations now average eight blocks apart and are about two blocks long. The platforms then occupy 25% of the length of line. Since there are two platforms to a station, i. e. one on each side vof thev tracks, it :follows that if we could stagger the upand-down stations, or place them end to end on an island platforn'i instead of on the opposite sides of the same street, they would occupy of the length of the line or, if they could be made continuous, would leave only 50% of the width of the platform to be accounted for in constructinga subway with a continuous island platform. ln other words, the space now utilized for loading platforms if properly distributed would provide a continuous platform of about 50% the normal platform .vidth. rl`he other50% may be gained withoutl increasing the over- Fig. 7 They comprise the spaces indicated at M which can be gained by removing the struction, are indicated by the dash lines in duct'benches Y found upon both sides of most of the present subway lines, and which now serve as an emergency walk for the passengers in case a train is stalled between stations, and placing the ducts or cable conduits 'under the center platforms as illustrated in Fig. i and Fig. 6, and the spaces indicated by N plus the width ofthe spaced center columns X which may be gained through the reduced amount of clearance required between the center line of the tracks and a platform as comparedto the clearance required between the center line of the tracks and the face of a column.

To consider 'a specific example of certain of the New York subways illustrated in Fig. 5, in the case of cars now in use, ,thel distance from center line L of the tracks T to inside facev of the wall `W is 7 3, and that to center of interior column X is Gf 6, making a total of 13 5), or net inside width of a two-track structure of 27 6". 'he in- ,sidewidth at stations averages 46 7 and since the stations occupy about of the vtotal vlength of line, the average width of the structure is Toer se sa,"

Under the new system illustrated in Figs. land 6 with the duct benches Y removed from the sides we shall require 6 3 from center line L of tracks to inside face of wall `W, and if 91/2 to edge of platform D or a total of 22A l for the two tracks, leaving 10 21/1 for a continuous platform D, `without increasing the average width of the subway. i Y By this system the space for the platform D is then'gained from the three spaces of the present system, thatis, from the space now taken for the present stations, the `space M now taken by the duct benches Yand the space N gained by the reduced clearance required from the center line of the tracks to- Y a platform as compared to the space rethe face of a column.

quired from the center line of the tracks to The width of platform D could of course be increased if the 10 2% is found insufficient by slightly increasing the overall width of the system.

mezzanine C may be continuous with the n platform vD or mayv be discontinuous but located at frequent intervals over the stairways cl at or between stations;

` As 1t 1sl usually necessary to excavate to the depth indicated to allow proper en-f trances tothe platform D, it willinvolve very little 'additional expense to construct continuous mezzanines C over the tracks in whichv case they maybe used to supplement the sidewalks or for stores or various other'purposes.

By having frequent entrances tothe continuous mezzanine C or to the continuous platform D, the walk to and from stations` may be made underground, whereby the passengers may walk to and from their desm tinations without interference from street trafic.`

Due to its substantiallyuniform overall width, this type of continuous platform subway will be simpler than the present one and the work of designing, constructing and .supervising construction much simplified. The elaborate station of the present type and its approaches could be dispensed with for all that isneeded is a series of narrow stairways leading directly to the platform D or to the mezzanine C with either manor passimete'r controls. In view of these economies the new type of subway with a continuous-platform can be built without iucurring additional expense as compared with the present types, but at a substantial saving when the increased capacity of the new type is considered.

Another advantage of my system is the added safety and security that vwill be gained by the travelling public through the fact that they are always alongside a platt'orm and not far from an exit; 'and that Y if anything happens to a train they are on, they can be let off immediately instead of lhaving to be shut'up in a 'tube',probably dark and smokafilled, for a long period, or be obliged to brave the third rail.

O pemtz'on.

The present local-express system, while highly desirable from the standpoint of economy of operation, and as a convenience to the travelling public, does notwork out so satisfactorily from the standpoint of maximum capacity for the. following reasons:

l. The vlocal and express trains are as a rule not operated independently, but are other at express stations. Inasmuch as the tendency `of this transferfis generally in one direction, the effect of it is to overcrowd one .system at the expense of the other. An observation of conditions at almost any point lof such a system will-show that while neither express nor local trains lack in patronage, one, usually the express, always is very much l more crowded than the other; and if the degree .of congestion of the former be. taken as 100%, the other would be only 50% full.

The result is'that while we operate af d-track system, we have as far as capacity is concerned, no more than, say a B-track line.

2. l.Vith practically 100% vof the local trallic changing for the express at express stations, these stations become over-congested which results in great confusion and delay, and a general upset of schedules.

To increase the carrying capacity and gain other important advantages, I propose to dispense with local and express trains and to `operateall trains on the basis of alternate trains` making alternate stops. In other words, every A train, A1, A2,` etc., will stop at the A stations indicated in Fig. 2 and skip the B stations, whilethe following B trains, B1, B2, etc., will reverse the process and skip the A stations. By bringing thev stations somewhat closer together than they average now, and taking advantage of the end controls or entrances, the maximum walk between the alternate A or B stations would not be much greater than under the present system, at the same time the schedule speed.

and carrying capacity of the railroad under the skip stop method of operation will materially improve.

The first effect of this method of operation would be to reduce the headway. The train headway is composed of two elements-(l) ruiming headway and (2) station headway. The running headway is the time interval between corresponding points of two trains moving at maximum speed; the station headway is the additional loss of time due to stopping at stations. Under the most exacting requirements of the block signal system, trains can be run at one minute in-` tervals with absolute safety. The station stops, however, impose a loss of another minute composed as follows:

` Seconds. Acceleration 111- D'eceleration 9.2 Station stop [Miscellaneous 6.8

Total 60.0

By adopting the alternate skip `stop method of operation here suggested, the headway can be reduced by 30 seconds, for 'the station headway loss will be divided by two trains speed without stopping, then train A2 will only have to be separated from train Blby the running headway which is one minute and will pass by the station A', three minutes after trainAl, instead of four minutes after.- ln brief, by this method of operation, the time interval between any alternate trains is equal to twice therunning headway plus one station headway.

This method of operationmay also be used to furnish us with the equivalent of a reservoir, or double track loading station, without the objectionable features of turn-outs,

short radii curves, costly approaches and ex. i

tra tracks. Like a reservoir station thi. method will permit two consecutive trains on the same track to load and unload at the same time and the headway will generally1 be determined by the running headway, rather than the stat-ion headway.

The operation of this system is shown on the accompanying diagram of Fig. 1, in which horizontal dimensions represent distance and vertical dimensions, time. Eachv horizontal space represents 250 feet, or one block, and each vertical space represents 20 seconds. Stations A B A B are indicated by heavy lines on thebottom of the diagram. These .are indicated on the diagram as being two blocks long and six blocks apart. The diagrams represent train performances and are based uponthe following: Maximum speed miles per hour.

Acceleration 1.25milesper hour per second.

Deceleration 1.9 miles per hour per second.

Station'stop 30 seconds.

Trains are designated A1 A2, B1, B2, etc. A trains will stop at A stations, and B trains at B stations. In practice `they will similarly be designated andv passengers boarding an A train will know from experience or from lists posted in every car, and at frequent intervals in the station where the trains will stop.

Capacity.

13 30=390 cars per hour.

Under my new system, operating under a 90-second headway basis, we shall get on one track, a capacity of 10 40z400 cars per hour.

track, however, merely represents the initial capacity of a highly elastic system, which capacity could be increased almost 10% by merely adding one car to the train, no increase in the station length being necessary, if we have a continuous platform as above described. A two-car addition would mean almost a 20%v increase, and by the time a QO-car train is reached, we shall practically have double the capacity of a four-track system on a two-tiack line, and a 20-car tiaiii by no means represents-the limit of the continuous platform system.

Signal system.

A signal system which may be used in the new construction and method of operation is shown diagiammatically on the upper portion of the diagram of Fig. 1. 'lhe system here illustrated conforms in essence to all requirements of a standardv system.

A block length is composed of two overlaps, each overlapconsisting of no less than a braking distance.' v j -At the entrance to each .overlap there are two signals, one home, indicating the condition of the track in the same block and one distant, showing the condition of the track lin the block ahead. vA train is thus always X1 X2 X3 etc. and distant signals byA Y1, Y2, Ya, etc. l'With train #l occupying overlap D, home signals X2 and X2 will be set for danger and distant signals Y1, Y2 and Y3 for caution. Train 'ft2 following will find the signal X1 clear and the caution signal Y? effective to indicate caution and the train will be permitted to proceed at a reduced speed to the entrance to overlap C, where the signal X2 will indicate danger and the train forced to come to a standstill or be tripped on passing the signal. Y

The workings of the signal system are shown on the train curves. j l/Vhen the train A2 enters overlap C1 atpoint a,it sets up a danger signal, which position is detery Ajectionable, as the slowing down and speed-1 mined by the intersection of this space point with the correspondingI time .point f120. This position is at b, lThis signal will 1remain yup until the end ofthe train has cleared the forward-end of the overlap at @ZS". Since the trainis 500 feet long, the forward end of the train will at that time occupy position e, corresponding to 140 on the time scale, see e. Projecting thisvpoint to intersect with space point .a `at f kwe get nof" as, the dangensignal for the time any portion of train A2 occupies overlap C1.

, l` lVliile the train occupies overlap D, another The capacity of 400 cars per hour on one danger signal will be set up at the saine location shown on the diagram as,g1,.,v While the train occupies overlap E, a caution signal will be set up shown by kl, In a similar way, all the other signals have been constructed. VIt is thus seen that at any point there are two danger signals indicated in full line, and one caution signal indicated by dotted lines `separating two moving trains, and that there-is an additional, interval of tiine'betweenthe forward `end of nal ahead. For convenience of plotting, the

length of overlap was taken as l500 feet,`

which represents the braking distance -plus about 10%. lt will be seen frointhe diara moving train aii-d theneaiest caution siggram 'that a considerably longer block could be used for the conditions under consideraj the constraint that is nowfeltat express staiooV will operate with perfect freedom, vwithout i tions, without reducing the block `length at stations and without having` to resort'to the i time control signals. lt might be vthought at first .that the reductionioffthe headway fromtwo minutes to ninety seconds, would place the operationuiider a stiain.- That the reverse is true is evident from what was just broughtout. This propertywould iinpart resiliency to the system, and in caseof `'one train being delayed the re'st of the' sys'- `tein will not be affected by it as quickly as under the present system. v y.

Another important feature of vmy invention will be seen from the following analysis.

By moving the station through one complete block, itV can be seen by inspection Y signals, except at one point.

ment of station B to the right would cause the'train curve to cut caution signal ma,

While from the standpoint of safety, there lis nothing objectionable to a trains entry' .into a caution zone, from the standpoint of y i econon'i H of .-oaeratinit Uenerall is obing up again in dresult is a, lossl of time and Tenergy. In Iouricase, however, there would be nothing 'objectionable to it from either standpoint, for the train on' entering the caution zone vwill be under full control of the brakes, and `on the road to a complete standstill, so that no further speeding up will be'required. This means that we shall be` able to lay out a system for the new subway at random with nothing but the braking length to be guided by and then lay out our station where we choose, and still be able to maintain our 90 second headway. Similarly, weshall be able to relocate a station without'havingto change the signal system.

y Power consumption. y Under the skip-stop system vthe' reduction:

- inthe number of stopscan be made about 40% less than in the present system without increasing the walk to and from stations. Inasmuch as the acceleration consumes about 80% of the total power necessary to operate the local trains, it follows that by reducing the brakes without having to repeatedly stop andI start as isoften the case at present. This will practically eliminate all stops between stations as a result of traiiic congestion and', in addition to other advantages, will result in av further reduction in the power consumption. A total saving of 50% in thepower consumption as a result of these two features is not impossible.

Power pla/n.25 capacity.

As a result of reducing the power 50% as'above, the power plant capacity may be correspondingly reduced.

A further reduction in the power plan capacity :made possible by the skip-stop method ofoperation will become apparent from an examination of the diagram of Fig. 1. It` willv be seen that in a stretch extending over five stations, or about 625 i feet, the accelerating periods P are uniformly scattered over the. entire stretch, each lasting about 86 seconds, and by spacing the sub-stations in such a way that each will feed about 6250 feet of line or any multiple thereof, we would get a practically uniform load on the sub-stations and power plants, with the maximum load but little above the average; v

It is of course not essential' that the station platform be literal'lycontinuous, andl in ns1-e554 places where cross-overs are required or natural obstructions present, it'may be continued as an overhead or underground walk, or be omitted altogether.

An improvement which may be utilized when desired is a transfer station, where trains from both the A and B systems would stop, and passengers would be able to change from one systemto the other. This station may be an individual island platform with reservoir tracks, or else a portion of theregular'platform with trains from the two systems stopping end to end, and passengers .walking the length of the train forward or backward as the case may be. A side transfer' platforni may also be constructedl in special cases. In'either case, the same number of passengers willon an average change from the A to thefl system, as from B to the.. A system, and no undue congestion will be produced. ln this way every station on the line would be made accessible to all passengers, and the walking to and from the stations reduced.'

If one main line is to branch out into two lines in the outlying districts, then each of these lines may leither be operated as one A and one B, or else have A and B trains alternate on each. v

The invention has been described as applied to a twov track syste-m, and as the capacity of the two tracks with a 20 car train will substantially equal thepresent capacity of ank 8 track system it will probably not be necessary to increasel theV num# beriof tracks. However, it could be equally well applied to any number of tracks, forl example, in Fig. 3, a four vtrack system is illustrated wherein the local tracks F "and G are located in the center ofthe street Yat each side of the continuous platform (l and the express tracks H and I are located i at the edge of the street outside the local tracks, suitable platforms E and E being provided` outside the express tracks with mezzanine or underneath passages where pessen'gers may transfer from one platform to the other. The express trains K may also be operated upon the alternate skip-stop system so that passengers from local A trains may transfer at stations E', and passengers from B ytrains may transfer at stations E", or each express train may make every express stop as under the present systems. In lieu of a four track system with both 'express and local trains, the four tracks may be operated as two separate two track local systems of the type previously described, by

providing a continuous island platform be'- tween.y each pair of tracks, or one of the two 'track continuous platform systems may be operated as a local system and one 'as' an express system. p Due to the skip-stop operation and the reduction in the number of stops and in the train headway, the operation of the system may be speeded up so that the speed of the skip-stop local trains compares favorably with the speed of the present express trains, giving as one result of my invention a two track system with a carrying capacity practically equal to the present four track system and a yspeed practically equal to the express train speed of the present system.

This feature may also be used in the operathe invention, it is to be understood thatA the continuous platform could be used with the present method of operation or that the skip-stop system could be used without the continuous platform and it is my intention to include these and other modifications of my invention within the scope of the appended claims.

llVhat l claim is:

l. A method of rapid transitsubway railway operation for multiple car trains which comprises stopping alternate trains at alternate stations arranged along a continuous platform. p

2. A method of rapid transit subway railway operation for multiple car trains which comprises stopping alternate trains at alternate stations arranged along a continuous island platform.

3. A rapid transit subway system for multiple car trains characterized by the use of a continuous island loading platform, whereby the locations of the stations may be readily changed.

4. A rapid transit subway system for multiple car trains characterized by the use of a continuous loading platform, whereby the length of trains operated is unlimited.

5. A rapid transit subway system for multiple car trains characterized by the use of a continuous loading platform constituting a series of stations, and frequent entrances at and between stations. 1

6. A method of rapid transit railway operation which comprises stopping alternate local trans at alternate local stations and alternate express trains at alternate express stations, and stopping all trains at some stations whereby universal transfers may be made.

7. A method of rapid transit railway operation which comprises stopping alternate local trains at alternate local stations arranged along a continuous platform and alternate express trains at alternate express stat-ions and stopping all trains at some stations whereby universal transfers may be made.

8. A method. of rapid' transit railway operation which comprises stopping alternate local trains at alternatelocal stationsl arranged along a lcontinuous island plat `form rand alternate express trains vat alternate express stations and stopping all trains at some stations whereby universal transfers may be made.

9. A method of rapid transit railway operation which comprises stopping alternate local trains at alternate local and express stations and stopping express trains at all express-stations.

,10. A rapid transit systemcharacterized y,

local tracksl at eachside ofthe platform,

express tracks outside the` local tracks and i parallel therewith, and express stations outside the express tracks whereby the tracks may be approximately straight and no change in the tracks is necessitated by changing the lengthof stations.

13. A subway system lof substantially uniform width having a substantially continuous loading platform `and substantiallyv straight tracks on either side thereof.

14. A transit system including continuous loading platforms constituting a series of stations and a signal system arranged to automatically maintain two danger signals and one caution signal between trains and also arranged to permit the location of the stations to be charged without interfering with the operation of the .signal system.

l5. A method of'increasing thefcarrying capacity of a rapid transit system which comprises stopping alternate trains at alternate stations, whereby the train headway is reduced, and using continu-ous platforms with substantially straight tracks whereby the train length may be readily increased.`

16. In a transit system, a plurality of stations, so spaced that a train leaving one of said stations without restraintwould endanger a train standing at the next station in advance, and a signal system comprisingv means controlled by the presence of a train at the advance station to maintain a warning signal at the other of said stations whereby signal stops between stations are ordinarily avoided.

17. A transit system comprising a succes- Vby the use of a continuousfisland platform,

itil) sion of stations for use by alternate trains on ACf:

train in the block of the next station .in advance7 whereby the station retardation of said trains may be overlapped to enable the station headway between trains to be reduced block including a danger signalr and a warnp ing` signal, the signals being so arranged that the presence of a. train at one station will' cause a warning signal to be set at the next Vpreceding station so that the checking' of speed required by the warning will coincide with the scheduled stopping orthe station.

19. A rapid transit system in which alternate trains stop at alternate stationsysaid system being divided into signal blocks of substantially equal length7 each block including danger and warning signals at its entrance and danger'and warning signals midwaybetwn its ends, controlled by the presence of trains in the block and in the blocks in advance so as to maintain two danger signals and a warning signal between trains, the blocks being of a length corresponding substantially to double the safe braking distance of a train, the arrangement of the signal system being such that the stations can be located at any desired distance apartv rso long as each station is spaced from the'station in advance of it at least far enough to have two danger signals and a warning signal interposed between trains atv said staF tions.

'20. A method of transit operation which comprises running a succession of trains on the saine track with less headway-thanv the sum of the timey required for a` station stop and the necessary running headway and stopping alternate trains at alternate stations whereby the station retardation of the successive trainsfis overlappedv and retarda` tion of trains by those preceding them is ordinarily avoided. i

21.A In al transit system, the combination with a plurality of stations, of'a signal system comprising a series of blocks arranged in overlapping relationq each block being equal in length to double the safe braking distance of a train? and each block being overlapped by two adjoining` blocks which meet at its middle so that the track is divided into block overlaps equal in length to the safe braio ing distance ot a train, the arrangementbeing such that a train is always in two overlapping blocks7 each block having a danger signal and a caution signal at its entrance made efecti've by the presence of a train in the block, the caution signal being also made'efective by the presence of a train in the advanced overlapping block.

Tn testimony whereof l have aiXed my signature to this specification.

PHILIP snor-is.

Certificate of Correction.

Parent No, 1,616,554. Granted February s, 1927, no

PHILIP SACHS.

It is hereby certed that error appears in the printed specicaton of the ab0vementioned patent requiring correction as follows: Page 7, line 106, claim 14, for the Word charged read changed; and tha-t the said Letters Patent should be read With this correction therein that the same may conform to the record of the case Vin the Patent Ofce.

Signe-d and sealed this 8th day of March, A. D. 1927.

[SEAL] M. J. MOORE,

e Acting 00mm/stione? of Patents.

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