Method of collecting traffic information, and system for performing the method

Via a cellular radio communication system, measured values are transmitted from vehicles to a computer. The measured values are chosen so that they can be used to determine Origin-Destination matrices without infringing upon the privacy of the users.

BACKGROUND OF THE INVENTION 
The invention relates to a method of collecting traffic information by 
receiving measured values, transmitted from at least one vehicle, in 
respect of location and movement of the relevant vehicle. 
The invention also relates to a system for performing the method. 
A method of this kind is known from the article "Ali-Scout--A universal 
guidance and information system for road traffic", R. von Tomkewitsch, 
Second International Conference on Road Traffic Control, 15-18 Apr. 1986. 
The cited article describes a traffic guidance system in which vehicles 
comprise a navigation device which guides the user to a preselected 
destination by means of a position-finding device and data concerning the 
local road network and current traffic situation as generated by a central 
computer and transmitted by guidance beacons. For traffic-dependent 
guidance it is necessary for the central computer to have available 
current traffic information which is provided by the vehicles themselves, 
the vehicles transmitting measured values (such as travel times and 
waiting times on route segments determined by the guidance beacons) to the 
guidance beacons which transmit this data to the central computer for 
processing. 
It is a drawback of such a method that it requires a complex and expensive 
network of guidance beacons with infrared transmitters and receivers in 
the vehicles as well as in the beacons. 
SUMMARY OF THE INVENTION 
It is inter alia an object of the invention to provide a less expensive and 
more efficient method. To achieve this, a method in accordance with the 
invention is characterized in that said measured values are defined 
relative to virtual reference positions and are transmitted in a cellular 
radio communication system via the communication mechanism of an actual 
cell. A cellular radio communication system, for example as introduced in 
Europe in 1991, offers an extensive mobile and portable communication 
network enabling vehicles or other users to transmit and receive digitized 
data via a radio link. The use of radio channels in this system and the 
definition of the data relative to virtual reference positions renders the 
network of guidance beacons superfluous. For more detailed information 
regarding this system, reference is made to the article "Implementing the 
Pan-European Cellular System", J. R. Easteal, Pan-European Mobile 
Communications, Winter 1989/90, IBC Technical Services Ltd, pp. 101-104. 
A preferred version of a method in accordance with the invention is 
characterized in that per vehicle the transmitted measured values contain, 
for each intersection passed, indications in respect of a route segment 
travelled by the vehicle so as to reach the intersection as well as in 
respect of a route segment travelled by the vehicle beyond the 
intersection. This offers a special advantage in that these measured 
values can be used to determine the so-called Origin-Destination (O-D) 
matrix for each intersection, and hence the O-D matrix of an entire area, 
without infringing upon the privacy of the user. For a given set of 
origins and destinations such an O-D matrix provides the frequencies at 
which vehicles depart from a given origin to a given destination. This 
enables authorities not only to improve the traffic infrastructure (for 
example by readjustment of traffic lights), but also to generate 
short-term traffic guidance recommendations to stimulate the flow of 
traffic. The data necessary for determining O-D matrices is customarily 
collected by means of video cameras monitoring the traffic flows at each 
intersection. This is a cumbersome and expensive approach, notably when 
the measurements are often repeated in order to update the data. The 
measured values transmitted in the cited Ali-Scout traffic guidance system 
are not suitable for calculating O-D matrices. An obvious solution to this 
problem would be the additional transmission by the vehicles of their 
destination; however, this has a major drawback in that the privacy of the 
users is then seriously affected. The method in accordance with the 
invention offers sufficient data for the determination of the O-D 
matrices, it nevertheless being impossible to trace individual users even 
in the case of low traffic densities. It is to be noted that this 
preferred version of the method can in principle also be used without a 
cellular radio communication system; however, in that case facilities must 
be provided at each intersection for the transmission of the data which 
is, of course a drawback.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 shows a number of cells of a radio communication system. In this 
case they have a circular shape with adequate overlap for full coverage of 
a region. Other cell shapes, of course, are also feasible. A cell of this 
kind corresponds to a geographic sub-region of a larger geographic region. 
Within the cell there is situated a transmitter/receiver station S whereto 
vehicles within the relevant cell can transmit data via a radio link. Each 
cell has its own radio frequency or radio channel and the range of the 
transmitter/receiver station is decisive as regards the dimensions of the 
relevant cell. The vehicles comprise a number of sensors (for example, 
magnetic sensors for direction finding and wheel sensors for determining 
the distance travelled) which, on the basis of their measurements, enable 
accurate determination of the location and the direction of movement of 
the vehicle by a navigation device, for example, the CARIN (Car 
Information and Navigation System) system, aboard the vehicle. To this 
end, the navigation device has available a digitized map of the area (for 
example, on CD-ROM) which contains all roads, composed of route segments, 
of the relevant region. Hereinafter, the term "intersection" or "junction" 
is to be understood to mean: any point of the road network where a vehicle 
can make a choice as regards continuation of its travel (i.e. three-forked 
roads, intersections, roundabouts and the like). Each segment of the road 
network between two intersections will be referred to hereinafter as a 
"route segment". Thus, a vehicle can determine at any instant its position 
on the map, i.e. which route segment is being followed at that instant. 
The digitized map forms a reference framework consisting of virtual 
reference positions. The measured values transmitted to the 
transmitter/receiver station S of a cell by a vehicle are defined in 
relation to these reference positions (for example, representations on the 
map of intersections or fuel stations along a highway); for example, a 
transmitted travelling time relates to the complete route completed 
between two given intersections. Therefore, the reference positions need 
not be represented by physical units such as beacons. The 
transmitter/receiver station S of each cell communicates with a central 
computer which collects and analyses the transmitted measured values. On 
the basis of the analysis of the traffic situation by the central 
computer, it can generate traffic guidance recommendations for 
transmission to the vehicles. The drivers of the vehicles can thus be 
informed about congestions caused by accidents, back-ups and the like. The 
flow of traffic is thus improved. 
FIG. 2 shows an intersection of roads. The traffic arrives from the 
directions or route segments numbered from 1 to 4. At this intersection 
each vehicle has the choice from three route segments for continuing its 
travel. Therefore, there are 12 traffic flows which are represented by 
arrows in the Figure. In a preferred embodiment of the invention, after 
passage of an intersection the following information is transmitted to the 
transmitter/receiver station S by each vehicle: an indication of the route 
segment followed by the vehicle so as to reach the relevant intersection 
and an indication of the route segment followed by the vehicle beyond the 
intersection. For example, a vehicle coming from the route segment via and 
continuing on the route segment 4 will transmit, after the right-hand turn 
at the intersection, the combination of the route segment 1 followed by 
the route segment 4 to the transmitter/receiver station S. Should a given 
vehicle temporarily not have the opportunity to transmit the data (for 
example, because the channel is busy), the indications of the route 
segments followed can be saved for a plurality of intersections until 
transmission of the data thus saved is possible. In such a case traffic 
will be rather busy, so that the privacy of the relevant user will not be 
affected, despite the transmission of the route indications relating to 
successive intersections. 
FIG. 3 shows an Origin-Destination matrix associated with the intersection 
of FIG. 2. The 12 traffic flows of the intersection have been counted 
during a given time interval. Evidently, this is possible only by way of 
the described transmission of the measured values in accordance with the 
invention. It can be seen from FIG. 3, for example that during the time 
interval of the measurement 89 vehicles originating from the route segment 
1 continued their travel via the route segment 4. Such an O-D matrix can 
also be translated (by simple normalization) into a percentual O-D matrix; 
the sum of the values of each row of the matrix is then 100. In a 
non-normalized O-D matrix, the sum of the values of each row represents 
the inflow via the relevant route segment and the sum of the values of 
each column represents the butflow via the relevant route segment. On the 
basis of this data, the authorities (the central computer) can optimize, 
for example the setting of traffic lights at the intersection. It is also 
possible to combine O-D matrices of neighbouring intersections, provided 
of course that they relate to the same time interval. Thus, for a given 
region an O-D matrix can also be determined from the O-D matrices of the 
constituent intersections of the relevant region. On the basis thereof the 
authorities can supply the users with traffic guidance recommendations via 
the cellular radio communication system. A major advantage of the 
collection of the traffic information in accordance with the invention 
consists in that the determination of the O-D matrices (or other 
measurements) can be simply repeated and hence continuously updated. The 
central computer can thus generate recommendations which fully correspond 
to the current traffic situation. The known step of making each vehicle 
transmit also its travelling time for its last route segment travelled 
thus also has a synergetic effect: in combination with the derived O-D 
matrices, even more accurate traffic guidance is possible. Another major 
advantage of the method in accordance with the invention consists in that 
the users need not make their final destination known. As a result of the 
transmission of the relevant route segments per intersection, the data 
required can be virtually anonymously collected. This is because it is 
impossible to track a given vehicle along its route through the cell, even 
in the case of low traffic density. The privacy of the drivers is thus 
ensured. 
FIG. 4 shows a device in accordance with the invention. Vehicle A comprises 
sensors SEN (for example, magnetic sensors for direction finding and wheel 
sensors for determining the distance travelled), a navigation device NAV 
with a digitized map of the geographic region which contains virtual 
reference positions, a radio unit R for transmitting and receiving data in 
a cellular radio communication system, and a microprocessor .mu.P. The 
microprocessor is programmed to apply the measured values from the sensors 
to the navigation device which utilizes this data for accurate 
determination of the location and the direction of movement of the vehicle 
relative to virtual reference positions on the map. The microprocessor is 
also programmed to transmit measured values, such as indications of the 
route segment travelled to a passed intersection and of the route segment 
travelled beyond the intersection, via the radio unit R, to the 
transmitter/receiver station S which communicates with the central 
computer CC. The transmitter/receiver station S and the radio unit R form 
part of a cellular radio communication system. The central computer CC 
receives measured values from a number of vehicles via several 
transmitter/receiver stations and processes this information so as to 
form, for example traffic guidance recommendations which can be 
transmitted to the vehicles via the transmitter/receiver stations. The 
microprocessor .mu.P in the vehicles applies this data to the navigation 
device which applies it to the driver of the vehicle. This can be realised 
in a visual manner, via a display screen, or audibly by means of a speech 
synthesizer.