Memory controlled process for railraod traffic management

A method for regulating vehicular traffic over a network of itineraries travelled by various vehicles such as railroad trains, or other public modes of transportation. On board, computer assisted vehicle control processes are advantageously combined with traditional time-table scheduling and modern centralized traffic control concepts. Simplified audio radio communications alleviate the need for intensive track equipment. Monitoring and signaling devices are limited to those dictated by safety rules and regulations. In order to limit to a minimum the exchange of data between each vehicle and the traffic control, a set of predetermined timetables are stored on board each vehicle. Traffic instructions are reduced to two elements, the identification of the assigned timetable and a time lag constant to be uniformly added to the time entries of the assigned time-table. The method relies on precise dead-reckoning equipment on board each vehicle which permits its operation in precise conformance with the assigned time-table. The dead-reckoning equipment which allows a continuous display of the exact location of the vehicle along its prescribed itinerary uses a combination of various conventional and novel techniques for the computation of the distance travelled. The most important of these techniques comprises the recognition along the itinerary of various planned and unplanned events which have been detected during previous experimental runs and recorded in coordination with their locations. Various cross-check and probabilistic choices are used in order to achieve a very high degree of accuracy and reliability of measurement. The method also contemplates the automatic control of the vehicle speed in function of prerecorded acceleration data, and of feedback information proportional to the time error computed in function of the assigned time-table and the dead-reckoning system display.

BACKGROUND OF THE INVENTION 
Railroad traffic management systems commonly in use today are based on the 
so called centralized traffic control (C.T.C.) concept, adopted in the 
U.S.A. in 1927. The most advanced adaptation of the C.T.C. concept is the 
ORE/LORENTZ/BBC system now being implemented throughout Europe. This 
method provides for close monitoring of each vehicle progress along its 
itinerary from a control center and regulation of its movement by 
communication of control instructions through signals and other equipment 
installed along the track. An itinerary for each vehicle is broadly 
defined in advance. Electronic data processing machines are then used to 
coordinate the various itineraries and to define signaling and switching 
instructions. The method relies upon powerful monitoring and decision 
making apparatuses at the traffic control center, and upon extensive 
detection, signaling and communication hardward installed along the tracks 
and between each track block and the traffic control center. The 
bidirectional flow of information between each vehicle and the traffic 
control center is not only frequent, but also lengthy and complex, since 
the progress of each vehicle along the track is totally dependent upon the 
directives of the traffic control center, with practically no control left 
to the discretion of its conductor. 
The trend towards centralized traffic control operation of railroad 
networks, based on extensive train location equipment along the track, has 
been prompted by two factors. On one hand the traditional inability of 
trains to accurately determine their position between stations prevented 
their engineers from making, on their own, the acceleration or breaking 
decisions necessary to reach a predetermined point on time, or to avoid 
collisions. On the other hand the unavailability of practical and reliable 
audio radio equipment severely limited communications between train crews 
and traffic stations. The centralized traffic control has greatly improved 
the efficiency of networks formerly managed by the traditional time-table 
method. Under time-table programming, trains were constrained to run 
within predetermined schedules. These schedules however, had large safety 
margins to guard against possible interferences with other trains. The 
network traffic capacity was thus severely limited. Today the time-table 
method of traffic regulation can still be encountered over some simple and 
lightly travelled circuits. 
The centralized method of traffic management, however, is not without 
disadvantages. Besides requiring a heavy investment in equipment and 
maintenance work, the method has other limitations. In spite of the 
repetitive nature of train schedules, the progress of a particular train 
over a frequently travelled itinerary is seldom similar from one run to 
the next. The train movement is subject to random pace variations dictated 
by the traffic control center in function of the current traffic condition 
over the network. The resulting braking and acceleration maneuvers 
increase the fuel consumption. Furthermore, the speed variations coupled 
with the uncertainty of the exact location of the train within a block 
create security risks. These risks can only be eliminated by increasing 
the minimum spacing between trains, thus causing additional delay, waste 
of energy and lower traffic capacity. 
Today's radio communications have been tremendously improved. Electronic 
miniaturization allows for installation of computer assisted 
dead-reckoning system on board each train. The task of the traffic control 
centers could now be safely and very efficiently alleviated by returning 
to the train crews (or to the train auto-piloting system) some of the 
track monitoring and decision making operations. 
SUMMARY OF THE INVENTION 
The method disclosed is a return to a new form of time-table traffic 
management, free from the former performance limitations, safe, and more 
efficient, although simpler, than the totally centralized method. The 
vehicle location and signaling equipment along the track is minimized, and 
dictated only by safety considerations. The frequency and contents of 
communications between the traffic control center and the moving vehicles 
are drastically reduced and can be carried over audio radio channels. 
The present invention teaches new method for accurately determining, on 
board a moving vehicle, its accurate position along an itinerary; and a 
new procedure for regulating its speed in order to meet its assigned 
schedule in response to said position determination. The method also 
teaches the use of stored control instructions (which may have been 
recorded during a previous run) in order to regulate the pace of the 
vehicle. Each vehicle can thus assume some of the control and 
decision-making normally concentrated at the traffic control center. More 
specifically the invention provides for storing on board each vehicle a 
set of predetermined time-tables. The time-tables are cross-checked two by 
two for compatibility and each vehicle is assigned a time-table and a 
time-lag to be added uniformly to the assigned time-table data. Accurate 
dead-reckoning equipment on board each vehicle provides a precise 
measurement of the vehicle compliance with its assigned time-table. The 
dead-reckoning equipment comprises conventional methods such as wheel 
revolution counters, and accelerometers. It comprises also the recognition 
along the itinerary of various planned and unplanned events which have 
been detected during previous runs and recorded in coordination with their 
location and timing data. Various cross-checks between sensors, auto 
calibration and statistical selection of data techniques are used to 
achieve a highly reliable position determination. The method also teaches 
the automatic piloting of the vehicle based on acceleration data recorded 
during experimental runs. These acceleration data are further combined 
with a signal proportional to the time error computed in function of the 
assigned time-table and the location displayed on the dead reckoning 
equipment. 
The principal object of this invention is to provide an improved method of 
time-table traffic management, whereby the coordination between various 
assigned time-tables can be defined, and the control directives between 
the control center and the vehicle crews can be exchanged, all in terms of 
a few simple parameters. 
The secondary object of this invention is to provide an accurate method for 
controlling the pace of a vehicle in exact compliance with its assigned 
time-table.

DESCRIPTION OF THE PREFERRED EMBODIMENT OF THE INVENTION 
Referring now to FIG. 1 of the drawing, there is shown the diagram of a 
hypothetical railroad network ABCDEF which comprises four itineraries. Let 
us assume that itinerary i (AEFB) is travelled from A to B by train Hi; 
itinerary j (DEFC) is travelled from D to C by train Hj; itinerary k 
(BFED) is travelled from B to D by train He; and itinerary 1 (CFEA) is 
travelled from C to A by train Hl. Let us assume also that the distances 
between locations ABCDE and F are those listed in meters in table G of 
FIG. 1, that train speeds are constant as listed in meters per second 
along with the length of each train in meters in table H of FIG. 1. 
Security regulations further dictate that the spacing between trains 
cannot at any time be less than 5 minutes. Given the above hypothesis, the 
regulation of such a network, according to the present invention may be 
achieved as explained below in order to process the four trains in the 
most direct method across the network, and with minimum supervision by the 
traffic regulating center. 
Each curve of FIG. 2A represents the most direct and fastest time-table for 
the corresponding train over its assigned itinerary. However, the diagram 
of FIG. 2A assumes that all four trains start at the same time (t=o) which 
leads to several conflicts that must be avoided by establishment of 
priority between trains, adjustment of speed, stop and wait periods or 
other delaying methods. According to the teachings of this invention, a 
distinct time-lag TL is added uniformly to each time-table TT so that, 
when the time-tables are compared two by two, no conflict can be found. 
This condition may be expressed between, for instance, the time-table of 
trains Hi and Hj as follows: 
EQU TL.sub.i .gtoreq.TL.sub.j +a.sub.j .multidot.l.sub.j +b.sub.ij 
if train Hi is to follow train Hj, and 
EQU TL.sub.j .gtoreq.TL.sub.i +a.sub.i .multidot..sub.i +b.sub.ji 
if train Hj is to follow train Hi; wherein TLi and TLj are the time lags 
added to the time-tables of train Hi and Hj respectively, li and lj are 
the lengths of trains Hi and Hj respectively, and ai, aj, lij and bji are 
constant factors established in function of the itineraries and trains 
characteristics. 
In our hypothesis ai, aj, ak and al are equal to the inverses of the speeds 
of train Hi, Hj, Hk and Hl respectively. The constant bij may be 
determined according to the formula: 
EQU b.sub.ij =Tc.sub.j -Tc.sub.i +SF 
Wherein Tcj is the time set in the basic time-table of the first train for 
passing at the "critical point" and Tci the time in the time-table of the 
second train corresponding to the same "critical point". For trains 
travelling in the same direction over a common path such as Hi and Hj from 
point E to point F, the critical point is the point of entry E if the 
first train is faster, and the point of exit F if the following train is 
faster. For trains travelling in opposite directions over a common path 
such as Hi and Hk, and trains Hj and Hl, the critical point is where the 
first train leaves the common section of tracks and where the second 
enters that common section. 
FIG. 2B shows the basic time-tables of trains Hi and Hj and how bij is 
determined in order to delay Hi so that Hi will travel the common section 
safely after train Hj. Hj being faster than Hi, the point E is the 
critical point. According to those time-tables, Tci=800s, Tcj=800s, hence 
bij=SF=300s 
FIG. 2C shows how bji is determined in order to delay train Hj so that it 
travels safely after Hi on the common path. The critical point is now F, 
Tcj=1200, Tci=1600 hence bji=1600-1200+300=700s. 
FIG. 2D illustrates how bik is determined so that Hi safely enters the 
common path after Hk has left it. In this case, E is the critical point. 
Hence, bik=250, and so forth. Accordingly, the following values are 
obtained: ai=0.2, aj=0.1, ak=0.0625 al=0.04 
______________________________________ 
bij=300 bik=250 bil=60 
bji=700 bjk=250 bjl=60 
bki=1400 bkj=1000 bkl=200 
bli=1500 blj=1100 blk=490 
______________________________________ 
A variety of 24 combinations of orders of priority is offered with 4 
trains. Let us assume that the selected order is Hl, Hj, Hk, Hj. The 
time-lags to be assigned to the time-tables must meet the following 
conditions, starting with TLl=0: 
TLj.gtoreq.al.multidot.ll+bjl; TLi.gtoreq.al.multidot.ll+bjl 
TLb.gtoreq.al.multidot.ll+bkl; TLi.gtoreq.TLj+j.multidot.lj+bij 
TLk.gtoreq.TLj+aj.multidot.lj+bkj; TLi.gtoreq.TLK+ak.multidot.lk+bik 
The above conditions are satisfied by the following time lag values, in 
seconds TLj=68 and TLk=1218 and TLi=1531. Adding these time-lags to the 
respective time-table eliminates all the previous conflicts. 
FIG. 3 illustrates the resulting timing diagram for the entire network 
operation. New time-tables with modified itineraries, new trains or 
different train speeds could be introduced into the above scheme. Such 
additional time-tables would have to be checked two by two against each 
other and against the previously established ones according to the 
procedure just described. The procedure would yield a new set of time-lags 
to be communicated to the respective trains in order to establish a new 
overall workable schedule for the network. Conversely, a vehicle crew may 
have to ask by radio communication, for agreement on an increased time-lag 
if for any reason it has been delayed, or they may report they had to 
switch to a lower grade time-table (slower time-table). 
The present method of traffic management may be readily adapted to networks 
already equipped with standard block signaling systems for avoiding train 
collisions. Rather than using a security factor SF in the form of a time 
constant as previously described, the values of bij are established in 
function of the restrictive signaling generated by the immediately 
preceeding train. 
The following example illustrates a method for determining bij on the 
previously described network subdivided in 1000 meters blocks, for trains 
Hi and Hj sharing a common path EF. Referring now to FIG. 15, given the 
slow speed of Hi, the distant signal at point M being the first 
restrictive signal to affect Hi if Hj has not cleared point E, bij is 
computed as follows: bij=Tcj-Tci where Tcj is the time at which Hj clears 
point E and Tci is the time when Hi clears point M. For the sake of 
simplicity, the above example assumes that both trains have constant 
speeds. It should be noted however, that the same method applies to 
variable speed time-tables, with or without safety signaling. Interference 
limit conditions for a vehicle Hi following a vehicle Hj without having to 
slip off its assigned time-table may always be expressed in condensed form 
through two constant such as aj and bij. 
The invention contemplates that all the time-tables applicable to a 
particular vehicle are stored in advance on board said vehicle. It follows 
that the overall regulation of the traffic over the network, according to 
the method just described, can be achieved by communicating from the 
traffic control center to each vehicle two simple instructions; to wit: 
the identification number of its assigned time-table and its assigned 
time-lag. This type of simple communication can easily be carried over 
ordinary radio channels. This method for regulating vehicular traffic over 
a network of interferring itineraries assumes that each vehicle has the on 
board capability of accurately complying with the assigned time-table and 
time-lag, or at least to be aware of any discrepancy as soon as it 
appears. 
FIG. 4 gives the general block diagram of the process carried out on board 
each vehicle. Block 1 represents a time of day clock synchronized with the 
traffic command center clock. Block 2 illustrates a memory in which the 
time-tables are stored. Block 3 indicates the dead-reckoning process which 
determines accurately the position of the vehicle along its assigned 
intinerary. The position coordinates px indicated by the dead-reckoning 
process 3 is used to address the time-table memory 2. The time tx at which 
the vehicle should pass the position defined by px according to the 
assigned time-table is read out of the memory and compared to the clock 
time ti modified by the assigned time-lag TL, in the comparator 4. The 
resulting time error .DELTA. tx is used in the vehicular control process 5 
to generate a acceleration or deceleration command .gamma. designed to 
reduce the time error .DELTA. tx to zero. In order to achieve a smooth and 
accurate operation of the system it may be necessary to instantaneously 
detect and measure the time error .DELTA. tx. Quasi-continuous time-tables 
are provided to that effect. 
In the time-table memory 2, the vehicular positions P.sub.1, P.sub.2, 
P.sub.3 etc . . . are recorded in relation to clock time t1, t2, t3 etc. 
as shown in FIG. 5. These memory data may be generated, a priori, in the 
laboratory. Preferably they should be established by entering the values 
generated by the clock 1 and the dead-reckoning process 3 during an 
experimental run of the vehicle. This latter method guarantees that the 
time-table can actually be duplicated by this particular vehicle during 
future runs. FIG. 12 illustrates the process used during such an 
experimental run. 
The control process 5 may be accomplished by the conductor of the vehicle 
himself in response to a display of the time error .DELTA.tx. Preferably 
it is done automatically according to the auto-piloting method illustrated 
in FIG. 6. It should be noted that the time indication tc issued from the 
clock 1 must be reduced in 6 by the assigned time-lag TL entered by the 
operator. 
In a second memory 9, are stored the instantaneous acceleration or 
deceleration commands to be applied to the vehicle in relation to the 
vehicle position px. These commands are also cross-related in the memory 
10 to the times tx corresponding to the position px according to the 
assigned time-table. These acceleration or deceleration commands can be 
computed a priori and entered in the laboratory. Preferably they are 
recorded during an experimental run of the vehicle over the corresponding 
itinerary, according to the procedure illustrated in FIG. 13. During 
subsequent runs command datum .gamma.ex is extracted from the memory 9 in 
function of the position coordinate px issued by the dead-reckoning 
process 3, to which a correction factor corresponding to the product of 
the speed vx by the response time, TR of the vehicle to acceleration or 
deceleration commands is added at 8. Command datum .gamma.et is extracted 
from the memory 10 in function of the time te derived from the clock after 
adding the response time TR to the time Ti, in 7, so that te=tc+TR-TL. A 
selector circuit 13 allows .gamma.ex to reach adder circuit 14 only when 
.gamma.ex value is negative or corresponding to a deceleration command. 
The command .gamma.et is fed to adder 14 only when it is positive and 
corresponding to an acceleration command. The command data .gamma.ex and 
.gamma.et should theoretically be sufficient to allow the vehicle to 
faithfully duplicate the experimental or theoretical run the 
characteristics of which have been stored in the memories 2 and 9. 
However, the inherent inaccuracy of the various organs of the vehicles 
would tend to cause a drift away from the time-table schedule. An 
additional acceleration or deceleration component .gamma.x is thus 
generated in 12 in function of the time error .DELTA.tx according to the 
formula: 
EQU .gamma.=A.DELTA.tx+B(d.DELTA.tx/dt) 
wherein A and B are constant factors determined in accordance with the 
characteristics of the vehicle the itinerary and other contingencies. The 
acceleration or deceleration .gamma.x is then added to .gamma.ex or 
.gamma.et in adder 14. The resulting value .gamma. is used to control the 
vehicle traction and braking machanism 27. The value .gamma.x thus acts as 
a corrective feedback to the command data .gamma.ex and .gamma.et. The 
process and equipment just described and illustrated in FIG. 6 constitutes 
a form of auto-pilot with two components which can achieve great accuracy 
and safety of operation. 
The dead-reckoning process 3 is illustrated more explicitly in block 
diagram form by FIG. 7 of the drawing. The basic principle for achieving 
great accuracy in dead-reckoning, in accordance with the present 
invention, is to use multiple measurement techniques which are then 
cross-checked and statistically interpreted. 
Various types of distance measurement techniques and devices may be 
advantageously used within the scope of this invention. For the sake of 
explanation, an acceleration technique and a wheel revolution counter 
technique will be specifically discussed. The first measurement chain 
comprises a wheel revolution counter 15 associated with a long term drift 
correction circuit 16 to indicate the estimated distance travelled pc. 
The second measurement chain comprises an accelerometer 19 which is located 
on the vehicle structure so as to give an indication of the longitudinal 
acceleration applied to it. In a train locomotive this accelerometer 
should be located near the center of the moving body in order to reduce 
the effect of the lateral acceleration experienced during the negotiating 
of curves. In order to compensate for slopes and suspension deflections, a 
tilting correction generated by a gyroscope 29 is added to the 
accelerometer 19 output. The acceleration data are fed to a first 
integrator circuit 20 at the output of which the speed vx of the vehicle 
is read and displayed at 26. A second integrator circuit 21 is used to 
obtain the estimated distance travelled py. An increment selector 23 
periodically selects the distance increment indicated during the current 
measurement period from either pc or py. This incremented period may 
conveniently be in the order of one second. The selection function may be 
the sum of Q.sub.Pc and (l-Q).sub.Py where Q is the weight factor 
attributed to the revolution counter data. The selected increment is then 
added in 24 to the content px of a position display register 25 in order 
to generate the current position coordinates which is immediately entered 
into the display register 25 in place of the previous reading. 
It should be noted that the wheel-revolution counter and the accelerometer 
constitute two measurement techniques which appropriately complement one 
another. The accelerometer usually gives a reliable measure but its twice 
integrated output signal is subject to drifting. It is known that during 
periods of high acceleration or on uphill ramps, the traction wheels of a 
vehicle are subject to spinning. During the deceleration process the 
wheels are subject to skidding. The revolution-counter is thus a poor 
gauge of the distance travelled during these periods; but can safely be 
relied upon during long periods of constant speed or of low power 
application, to provide precise measurement on the basis of which the 
accelerometer can be recalibrated. The increment selector 23 operates in 
function of the raw, absolute value of acceleration and gives more weight 
to distance increments from the wheel revolution-counter in inverse 
proportion to the amplitude of the accelerometer output. A comparator 
circuit 22 is further added in order to generate a correction factor for 
the accelerometer and the speed indicator 26 in function of the error 
detected between pc and py during periods when the wheel 
revolution-counter can be expected to yield very reliable data. 
The combination of the two complementary measurement techniques can provide 
reliable positive data over a short run. For long distance, the slow drift 
accumulated by each method due to the systems components tolerances and 
inherent inaccuracies could result in substantial error, after several 
kilometers. The probabilistic correction circuit 18 in association with 
memory 17 is used to periodically correct the positive display register 
25, as described below. 
A well known method for automatically correcting dead-reckoning systems 
consists in installing along the track a series of check points evidenced 
by markers or contact ramps which can be sensed by vehicles passing over 
it. Since the location of these check points is accurately known their 
detection can trigger automatic correction of the position display data. 
In order to avoid the untimely correction of the position data triggered 
by spurious signals, check point detection equipment is, in its normal 
state, inhibited and allowed to operate only when the vehicle is 
approaching the area where it is expected to pass the check point, then 
shut-off again. The adjustment of the width of the window during which the 
check point can reasonably be encountered is often a compromise between 
two risks. First the risks that the check point will be missed altogether 
if the window is too narrow. Second, the risk that a spurious signal will 
be detected and mistaken for the check point if the window is too wide. 
The amount of applied correction in function of the detected error is 
shown by the function A of FIG. 8 wherein the distance between point M and 
N is proportional to the width of the window. 
The present invention teaches a method attributing a corrective weight to 
the detection of a check point in proportion to the probability that it is 
not a spurious signal. That probability is assumed to be in function of 
the closeness of the detected checkpoint position to its expected 
location. For instance, the correction could be done in proportion to the 
curve B of FIG. 8 which shows the correction weight to be in function of 
the difference between the known location of the expected check point and 
the current estimated location i.e., the estimated errors. This technique, 
which avoids the discontinuity of the correction function at points M and 
N, corresponds to opening a window with variable limits as evidenced by 
curve C of FIG. 8 which show the correction in function of the time error. 
FIG. 9 is a block diagram of the probabilistic correction process 
illustrated by curve C of FIG. 8. 
A memory 17, holds in storage the known measured location pex of each check 
point Ex. Upon detection of a check point Ex, its closest known location 
pex is extracted from the memory 17 and compared to the location px 
currently stored in the display register 25. A correction C is computed in 
function of the difference in 27 and added to px at 28. The resulting 
corrected px data is then entered into the display register. 
FIG. 9 also illustrates the block diagram of the process followed in 
correcting the slow drift error caused by variations in the wheel 
circumference due to wear and temperature variations. 
The wheel circumference factor W (multiplied in 32 by the number of 
revolutions N indicated by the counter 15) is quasicontinually adjusted by 
a minute correction factor .epsilon. added to it at 33. The correction 
factor .epsilon. is a function of the correction C applied to the display 
register 25 upon detection of a check point. This correction is computed 
in the correction circuit 31. A low-pass, integrating type filter 30 may 
be advantageously installed between the circuit 31 and the adder circuit 
33 in order to stabilize the corrective system loop. The exact location 
coordinates pex of each check point Ex can be determined by survey and 
written into the memory 17 in the laboratory. These coordinates can also 
be recorded during an experimental run according to the following 
procedure. 
The locations of the check points are measured and recorded using the 
dead-reckoning apparatus described above, limited to the two complementary 
measurement techniques as shown in FIG. 14. The recorded coordinates are 
then extracted and corrected in function of the measurements obtained 
through said limited dead-reckoning apparatus between two well known 
reference locations. The corrected values P1, P2, P3 etc . . . of the 
check points can be derived from the recorded coordinates p1, p2, p3 etc . 
. . through the following equation: 
##EQU1## 
wherein B1 and B2 are the true known coordinates of the reference 
locations and b1 and b2 their measured coordinates. 
The type of check points used in the first described correction process 
requires substantial investment for installation and maintenance. 
According to the teachings of this invention most of these planned events 
constituted by the encounter along the itinerary of premeasured check 
points can be advantageously replaced by the detection of unplanned events 
which have not necessarily been installed for that purpose. These 
unplanned events can be, for instance, a lateral deflection of the vehicle 
at a curve, the variations in vertical acceleration due to obliguity of 
the track, the variations in the amount of light reflected by the tracks, 
the variation of sound levels when the vehicle crosses a bridge or passes 
under a tunnel and a multitude of other recurring immutable physical 
phenomena detectable along a particular itinerary. Referring now to FIGS. 
7, 10 and 14, the method can be explained as follows: 
The various physical phenomena are first recorded in the course of an 
experimental data gathering run over the itinerary. The vehicle for that 
purpose is equipped with a plurality of sensors and transducers 39. The 
various output signals are processed through signal conditioning equipment 
38 then digitized into binary coded words which can conveniently be stored 
in a memory 17 in correlation with the location coordinates pex measured 
by the dead-reckoning system at time of their occurence. Each phenomena 
variation is thus translated into a event Ex which can be extracted from 
the memory 17 in function of its location coordinates pex. These 
coordinates can be corrected according to the procedure previously 
outlined. 
During subsequent runs over the same itinerary the estimated location px 
derived from the location display register 25 is sent to a probability 
limit circuit 34. This probability limit circuit define the two limits of 
an interval inside which the vehicle is supposed to be (with a probability 
of, for example ninety-nine per cent). These limits are computed in 
function of px and statistical factors such as a standard deviation and a 
multiplier n based on the estimated accuracy of the distance measurement 
equipment. The multiplier n, for instance may be proportional to the 
distance travelled since the last correction was made. The statistical 
limit circuit 34 generates two limits pxm and pxr which are applied as 
addresses to the memory 17. The coded events Exm through Exr corresponding 
to the addresses included in the margin defined by Pxm and Pxr are 
extracted and compared in 35 to the event currently issuing from the 
phenomena sensing equipment 38, 39. 
When identity of signals is found between the information extracted from 
the memory 17 and the information issued by the sensing equipment 38-39, 
the corresponding location coordinate Pxn which lies between Pxm and Pxr 
is transmitted to the correction factor generator circuit 36. In the 
correction factor generator circuit 36, the location coordinate Pxn is 
compared to the estimated location px and a correction value C is 
generated according to a function similar to that illustrated by curve C 
of FIG. 8. The correction value is then added at 37 to the estimated 
position coordinate px. The resulting corrected coordinates are then 
entered into the display register 25. The correction value C is also used 
to reset the variable statistical factor used in the statistical limit 
circuit 34. 
In cases where multiple informations within the Pxn Pxr margin are found to 
correspond to the incoming event Ex the correction value C is 
appropriately decreased in function of the uncertainty thus created. 
Although reference has been made throughout this specification to railroad 
installations, the method of traffic regulation disclosed herein may be 
applied to other forms of vehicular movements. These methods may be 
advantageously used in the regulation of maritime traffic in and out or 
within a harbor, as well as over a network of canals. Regulation of 
airborne traffic would also benefit from the application of some of the 
techniques explained above. 
The methods described above may be implemented through the installation on 
board such vehicles of electronic data processing equipment of both analog 
and digital types. The function sought to be performed are within the 
current state of the art and within the knowledge and capabilities of 
persons skilled in the electrical and mechanical arts. 
Although I have described specific means for implementing the methods 
disclosed herein, other means may be used for that purpose within the 
scope of my invention as defined by the appended claims.