A method of predicting a traffic behaviour in a road system

Abstract

The invention relates to a method of predicting a traffic behaviour in a road system, comprising the following steps carried out by at least one processor (9, 11, 14, 17) connected to a database (7, 12, 16), which contains a set of traffic profiles (6): clustering the traffic profiles (6); calculating a significance value (SV); if the significance value (SV) of a tag (T) is higher than a threshold value (TH), assigning this tag (T) as a characteristic vector (CVi) to this cluster (CLi); receiving a request (Req) having one or more request tags (RT); determining a cluster (CLi) by means of matching the re- quest tag / s (RT) to the characteristic vectors (CVi) of the clusters (CLi); and outputting a predicted traffic behaviour (PTB) based on the determined cluster (CLi).

Description

The invention relates to a method of predicting a traffic behaviour in a road system on the basis of a set of traffic profiles, each of which represents a traffic measure of vehi- cles in the road system recorded over time, wherein one or more pre-defined tags associated with a time of recording of the specific traffic profile is / are attributed to said traffic pro- file. The invention thus concerns the field of measuring and evaluating vehicle traffic behaviour, for example traffic be- haviour on a main street of a city. Once the traffic behaviour on this street has been analyzed over an extended period of time, typically over a year or longer, the aim is to estimate the traffic behaviour for a certain day or time-window in the future. This can be used to predict which road will be con- gested or blocked at a certain time, e.g., for freighters plan- ning the transportation of cargo or families planning their va- cation. Depending on the predicted traffic behaviour, different routes or times at which to travel on this street can then be chosen, whereby in any case the start-to-end journey time for a vehicle can be reduced. To this end, known methods of traffic prediction use a similarity clustering of the recorded profiles and an assigning of characteristic vectors ("labels") of tags to the clusters, which tags can be queried to identify a cluster of traffic pro- files as a predicted traffic behaviour for a certain day, e.g., a specific weekday, a "rainy" day, etc. Weijermars, van Berkom: "Analyzing highway flow patterns using cluster analysis", IEEE Conference on Intelligence Trans- portation Systems, September 13 - 16, 2005, shows a method for analyzing traffic patterns. Herein, 118 traffic profiles have been recorded for a highway, each over a time-span of 24 hours. Thereafter, the traffic profiles have been clustered by means of a standard clustering algorithm. After manually labelling the clusters, deviations within the clusters were evaluated. Instead of manually labelling the clusters, in the state of the art it is also known to find a matching label for clus- ter by means of a randomised algorithm. Such an algorithm takes up a lot of computational resources and has the problem that certain labels, which could accurately describe the contents of the cluster, cannot be found, because of few corresponding traffic profiles within this cluster. The invention sets its aim to create a more reliable and quicker method for determining labels of clusters, which can then be used to find a predicted traffic behaviour for a spe- cific request. To this end, the invention provides for a method of pre- dicting a traffic behaviour in a road system, comprising the following steps carried out by at least one processor connected to a database, which contains a set of traffic profiles, each traffic profile representing a traffic flow or a different traffic measure of vehicles in the road system recorded over time, one or more pre-defined tags associated with a time of recording of the respective traffic profile being attributed to said traffic profile: clustering the traffic profiles with their tags into at least one cluster, preferably into at least two clusters, as to similarity of traffic profiles; for at least one tag in each cluster, calculating a sig- nificance value by means of a statistical analysis; if the significance value of a tag is higher than a threshold value, assigning this tag as a characteristic vector to this cluster; in a prediction engine, receiving a request having one or more request tags to determine a matching cluster; determining a cluster by means of matching the request tag / s to the characteristic vectors of the clusters; and outputting a predicted traffic behaviour based on the de- termined cluster. The plurality of all characteristic vectors of a single cluster is hereinafter referred to as the "label" of this clus- ter. With the inventive method, labels of clusters can be de- termined in an efficient and systematic manner. By evaluating a significance value for a tag of a traffic profile within a cluster, it can be checked whether this tag is in fact a valid representation of this cluster. This partial statistical analy- sis of the cluster can be used to determine "first-level" char- acteristic vectors that only comprise one tag. In an exemplary embodiment of the invention, there are at least two variables, and each tag is assigned to a variable, the method comprising the further steps of for at least one variable in each cluster, calculating a significance value; and for a tag assigned to the variable with the highest sig- nificance value of each cluster, calculating the significance value. This has the advantage that a "pre-sorting" takes place, which makes the algorithm faster overall. The significance value for the variables can be determined in the same way as for the tags. In this exemplary embodiment, it is further advantageous if the method comprises the further steps of grouping all traffic profiles that do not contain a tag whose significance value lies above said threshold value to a sub-cluster; for at least one variable in the sub-cluster, calculating a significance value; and for at least one tag assigned to the variable with the highest significance value of the sub-cluster, calculating the significance value. The sub-cluster is thus used to "re-use" the traffic pat- ters that did not comprise tags with a significance level above the threshold level in the first iteration. Further preferably, in this exemplary embodiment the steps of grouping, calculating the significance value for a variable and calculating the significance value for a tag are repeated until no more traffic profiles are available for grouping. Here, sub-cluster after sub-cluster is created and evaluated for each variable to obtain all significant tags of the clus- ter. Furthermore, all of the above-mentioned steps can be re- peated for each variable occurring in a cluster to yield the broadest set of significant tags. Also "second-level" characteristic vectors of a cluster can be determined. A second-level characteristic vector is a combination of two tags, which are together representative of the cluster. Therefore, in a preferred embodiment of the inven- tive method, for at least one tag whose significance value lies below said threshold, a significance value of a combination of said tag with a further tag is calculated and, if said signifi- cance value of said tag combination lies above the threshold, said tag combination is assigned as a further characteristic vector to the cluster of said tag. Thereby, a level-by-level analysis of the representative characteristic vectors of a cluster can be made. For example, a cluster could contain traffic profiles which were recorded on Fridays in July. While neither "Friday" nor "July" is a repre- sentative characteristic vector of this cluster, the tag combi- nation "Friday in July" accurately describes the contents of this cluster and is a characteristic vector for this cluster. Preferably, a significance value of a tag combination is calculated for a tag that had the highest significance value during the "first-level" evaluation, while its significance value was still below a threshold value but preferably above a further "lower boundary" threshold level. For this tag, the significance value is determined in combination with all re- maining tags or just in combination with the most common of these remaining tags. A tag which has been used as a character- istic vector in the "first-level" evaluation is not considered to be a remaining tag. Further preferably, also "third-level", "fourth-level", et cet., evaluations can be performed as long as the significance value of a tag combination still lies above said further lower boundary threshold level. The threshold levels can change de- pending on the number of tags combined. In a preferred embodiment of the invention, for each clus- ter, significance values for all tags of this cluster are cal- culated. Thereby, it is not possible to miss out on character- istic vectors whose underlying tags are not very common in this cluster but still describe contents of this cluster accurately. For example, if the tag "Christmas" is the only tag within a cluster, the characteristic value "Christmas" is still signifi- cant for this cluster when the tag "Christmas" is a unique tag amongst the entire set of traffic profiles. Alternatively, only the most common or only arbitrary tags are evaluated. The clus- ter can thus be assigned a label which is derived in a fast, systematic, and reliable manner. In a further preferred embodiment of the invention, when two clusters would be assigned the same characteristic vector, the threshold value is lowered and it is again checked if the significance value of each tag (or tag combination) is higher than the threshold value to assign this tag (or tag combina- tion) as a characteristic vector to this cluster. By means of this, it is possible that an additional tag is added to the characteristic vector that caused the "double labelling" for two different clusters. Alternatively, the characteristic vector whose tag or tag combination, respectively, has the lower significance value is disregarded. This measure prevents collision problems when de- termining a cluster by means of matching the tags of the re- quest. In other words, the characteristic vector is discarded for a cluster when a different cluster has the same character- istic vector with a higher significance value. The significance value of each tag or tag combination can be determined by a variety of statistical analyses. In a first preferred embodiment, the significance value of each tag or tag combination, respectively, is calculated by means of a Chi- squared statistic. The Chi-squared statistic is especially pre- ferred in this method since it gives a highly accurate repre- sentation of the significance of a tag or tag combination within a cluster while at the same time considering tags or tag combinations of other clusters. Preferably, Pearson's Chi- squared statistic is used. It has been noticed that certain characteristic vectors always appear in same clusters. For example, Mondays, Tuesdays, Wednesdays, and Thursdays might exhibit the same traffic behav- iour, and characteristic vectors with tags relating to these weekdays can be thus be grouped together. By means of this, the determination of a cluster by means of matching the tags of the request can be sped up because the amount of characteristic vectors for this cluster has been reduced, e.g., in this case from four weekdays to one group of days. In some embodiments, the significance values of the tags or tag combinations are also used when checking whether a re- quest tag matches a characteristic vector. The determined sig- nificance value can thus be used twice in the method, firstly when labelling the clusters and secondly when determining the matching cluster. This is advantageous because characteristic vectors with higher significance values are more likely to match a tag of the request than characteristic vectors with lower significance values. In all embodiments of the invention, it is preferred that each traffic profile represents the traffic measure of vehicles in the road system over a time-span of 24 hours. Alternatively, times-spans of 6 hours, 12 hours or 18 hours can be used, too, especially when the traffic behaviour in certain hours of the day, e.g., night hours or rush hours, are substantially the same for all traffic profiles. Preferably at least one tag indicates a day of the week, a month of the year, a week of the month, a school vacation indi- cation, or a special holiday indication of said time of re- cording. Such tags can, e.g., be automatically generated by as- sociating an attribute of a calendar to a traffic profile. The calendar can be defined in advance, in real-time, or in retro- spect, and it is also possible to subsequently add tags to traffic profiles when they first occur in a request. Alternatively or additionally thereto, at least one tag indicates a road condition or a weather condition at said time of recording. Such tags represent a physical measurement of en- vironmental data, which can be coded by the tag in advance, in real-time, or in retrospect. The invention shall now be explained in more detail below on the basis of preferred exemplary embodiments thereof with reference to the accompanying drawings, in which: Fig. 1 shows a schematic view of a road system; Fig. 2 shows a block diagram of databases and processing engines for performing the method of the invention; Fig. 3 shows an example of clusters and associated labels occurring at the clustering and labelling stages of the method of the invention; Fig. 4 shows a decision tree used to determine labels for clusters during the method of the invention; Fig. 5 shows a flow chart of the prediction stage of the method of the invention; and Fig. 6 shows an example of the elimination of tags from the request during the prediction stage of Fig. 5. In Fig. 1 a road system 1 with a plurality of roads 2 is depicted on which vehicles 3 travel in directions R. The road system 1 is equipped with at least one traffic measuring device 4, which can be, for example, used for measuring traffic flow on a road 2 or on an intersection of roads 2. The traffic meas- uring device 4 may be mounted on a gantry 5 spanning the road 2 or may alternatively be mounted roadside. The traffic measuring device 4 can be embodied as any type known in the state of the art, e.g., as inductive loops, radar devices, light barriers, video processing cameras, or as wireless readers that read a radio response of so-called onboard-units (OBUs) carried by the vehicles 3. The traffic measuring device 4 can record the traffic flow on the road 2 directly, e.g., as a number v of vehicles 3 per time unit t, or it can record the number <semantics>v / t<annotation encoding="application / x-tex">v / t< / annotation>< / semantics> of vehicles 3 travelling on a given section of the road 2 at a given instant in time, e.g., by counting the vehicles 3 in camera pictures of said road section taken at regular time intervals. Instead of measuring the traffic flow, other traffic con- ditions on the road can be measured by means of different meas- urement values too, for example by recording an average speed on the road 2 at a certain point in time t or by measuring the travel time vehicles take to travel a section of the road 2. The traffic measuring device 4 records the traffic flow v / t - or equivalent measurement values as described above - per time t over a predefined time-span of, e.g., 24 hours as a traffic profile 6 (Fig. 2). Alternatively, shorter time-spans could be used, too, for example only the most interesting time- spans of, e.g., 6, 12 or 18 hours of a day. The traffic measuring device 4 records said traffic pro- files 6 over an extended period of time, e.g., day after day for a whole year or longer. A traffic profile can be made up of discrete samples, e.g., one sample each 5 min, 15 min, or each hour, or can be an at least partially smooth curve over time. In this way, each traffic measuring device 4 records a set of traffic profiles 6 for its road 2 or intersection of roads 2 and stores it in a database 7 via a data connection 8. A proc- essor 9 is connected to the database 7 via a connection 10 for further processing of the traffic profiles 6, as will be de- scribed in the following. Fig. 2 shows a clustering engine 11, which can be part of the aforementioned processor 9. The clustering engine 11 ob- tains traffic profiles 6 from the database 7 and clusters these traffic profiles 6 into at least one or at least two clusters CL1, CL2 ..., generally CLi. The clustering algorithm used in the clustering engine 11 can be of any type known in the state of the art, for example a hierarchical agglomerative clustering algorithm. To this end, the traffic profiles 6 might need to be pre-processed such that they contain, e.g., 96 time samples each at 15 minute intervals. Furthermore, filters can be em- ployed to deal with local anomalies occurring in the traffic profiles 6. As a result, the clustering engine 11 outputs clusters CLi, each comprising multiple traffic profiles 6 that are simi- lar to each other, to a database 12. This database 12 can be the same as the database 7 or a subset thereof. Furthermore, the clustering engine 11 can be controlled by means of a con- trol setting input 13 to adjust clustering parameters. After the traffic profiles 6 have been clustered to clus- ters CLi, a labelling engine 14 is employed to assign a label <semantics>L1<annotation encoding="application / x-tex">L_1< / annotation>< / semantics>, <semantics>L2<annotation encoding="application / x-tex">L_2< / annotation>< / semantics>, ..., generally <semantics>Li<annotation encoding="application / x-tex">L_i< / annotation>< / semantics>, to each cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, wherein each label <semantics>Li<annotation encoding="application / x-tex">L_i< / annotation>< / semantics> consists of at least one characteristic vector <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics>, <semantics>CV2<annotation encoding="application / x-tex">CV_2< / annotation>< / semantics>, ..., generally CVi. The labels Li should reflect the contents of the clusters CLi as accurately as possible. The method steps performed by the labelling engine 14 will now be described in detail by means of Fig. 3, which shows four exemplary clusters <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics>, <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>, <semantics>CL3<annotation encoding="application / x-tex">CL_3< / annotation>< / semantics>, <semantics>CL4<annotation encoding="application / x-tex">CL_4< / annotation>< / semantics> output by the clustering engine 11. The first cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics> comprises <semantics>N=100<annotation encoding="application / x-tex">N = 100< / annotation>< / semantics> similar traffic profiles 6, of which only four are shown in diagram 15 for ease of representation. Diagram 15 maps the time t on the horizontal axis and the traffic flow in vehicles per time v / t on the vertical axis. It can further be seen that each of the four exemplary traffic profiles 6 can have one or more, in the present example two to four, pre-defined tags T attributed thereto. The tags T attributed to a traffic profile 6 are associ- ated in some way with the time of recording said traffic pro- file 6. For example, a tag T can indicate a day of the week, a month of the year, a week of the month, a school vacation indi- cation, a special holiday indication, a road condition, or a weather condition at the time-span over which its traffic pro- file 6 had been recorded. The tags T can be attributed to the traffic profile 6 di- rectly at the time of recording by means of the traffic measur- ing device 4, at the database 7, or even after clustering at the database 12. To this end, the corresponding devices 4, 7, 12 can each comprise a clock, calendar, weather station, or any means to receive environmental or road condition data. Alterna- tively, tags T can be attributed to the traffic profiles 6 in retrospect, for example by means of calendars of the databases 7, 12. Calendar, weather, environmental, or road condition in- formation can be attributed in retrospect, for example if a week or a month later information arises that the road on which the traffic flow has been recorded was damaged or under con- struction. Tags T can even be attributed to the traffic pro- files 6 during the step of labelling by means of the labelling engine 14, which can have its own calendar or data inputs for this purpose. Coming back to the specific example of Fig. 3, it can be seen that a first traffic profile 6 of the first cluster CL1 has the tags "Monday", "rain", "normal day (no holiday)", and "June". A second traffic profile 6 of this cluster has differ- ent tags T, here "Monday", "sunny", "normal day (no holiday)", and "July", and so forth. To extract a label <semantics>Li<annotation encoding="application / x-tex">L_i< / annotation>< / semantics> that most accurately describes a cluster CLi out of all the tags T of this cluster CLi, the la- belling engine 14 firstly calculates a significance value SV for at least some of the tags T within this cluster CLi. In some embodiments, the significance values SV of all tags T of all traffic profiles 6 of a cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> are calculated, while in other embodiments significance values SV are calculated for only the most common tags T of the traffic profiles 6 of a cluster CLi. The significance value SV can be calculated by means of a Chi-square statistic. For example, Pearson's Chi Squared sta- tistic can be used if there are 5 or more traffic profiles 6, and an exact combinatorial method like Fisher's exact test can be used if there less than 5 traffic profiles 6. This yields a most accurate description of significance of an individual tag Τ. To evaluate if a tag T is in fact significant or not, the labelling engine 14 obtains a threshold value TH from a thresh- old input 15. The threshold input 15 can be adjusted manually or digitally if it is connected to computer. If the signifi- cance value SV of a tag T within a cluster CLi lies above the threshold TH, a characteristic vector <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> comprising this tag T is assigned to this cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, see Fig. 3 on the right. For the first cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics> of Fig. 3 it can be seen that four tags T within this cluster have a significance value SV lying over the threshold TH value, such that they have been stored as characteristic vectors <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics>, <semantics>CV2<annotation encoding="application / x-tex">CV_2< / annotation>< / semantics>, <semantics>CV3<annotation encoding="application / x-tex">CV_3< / annotation>< / semantics>, <semantics>CV4<annotation encoding="application / x-tex">CV_4< / annotation>< / semantics>. The corre- sponding tags T were "Monday", "Tuesday", "Wednesday", and "Thursday". The label <semantics>L1<annotation encoding="application / x-tex">L_1< / annotation>< / semantics> of this cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics> thus consists of four characteristic vectors CVi, each containing a single tag Τ. Fig. 4 shows an example of how to generate the label Li corresponding to the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics> and second label <semantics>L2<annotation encoding="application / x-tex">L_2< / annotation>< / semantics> of Fig. 3. Here, firstly the significance values SV of three tags "holiday", "Sunday", and "July" have been calculated. Assuming a threshold value TH of 90%, it can be seen that only the tag "holiday" with a significance value SV of 92% qualifies as a characteristic vector CVi. Additionally, significance values SV for combinations, i.e., "and"-combinations, of tags T can be calculated, either for all tags T whose significance value SV lies below the threshold value TH or for tags T whose significance value SV lies below the threshold value TH but above a further threshold value, for example 25%. For those tags T, the significance value SV is calculated in combination with a further tag T, and if the significance value SV of such a tag combination TC lies above the threshold TH (or a different threshold), this tag combination TC is assigned as a characteristic vector CV; to this cluster CLi. Depending on the method to calculate the significance value SV, it might be beneficial to also consider "or"- combinations insofar as they have not been already found in the form of multiple individual tags T whose significance values SV lie above the threshold level within the same cluster CLi. To this end, the significance value SV of an "or"-combination of two tags whose significance value SV lies below the threshold level TH is calculated to see if these are to be included each as a characteristic vector <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> for a cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>. Generally, this method can be performed also for tag com- binations TC comprising three or more tags T, for example when the significance value SV of a two-tag combination TC again lies in a specific range of thresholds values. By means of this, tag combinations of any length can be assigned to a clus- ter CLi as characteristic vectors CVi. One exemplary algorithm of identifying the significant tags T of a cluster CLi is given as follows. To begin with, the tags T are specific values of so-called variables V, e.g., variables V can be "weekday", "special day", "school vacation day", "month", "month week", and / or "weather condition". The tags T are in turn assigned to each variable V, e.g., tags "Mon", "Tue", Wed", ... to the variable "weekday", tags "holi- day", "pre-holiday", ... to the variable "special day", "Yes", "No" to the variable "school vacation day" and so forth. In a first step of the exemplary algorithm, it is deter- mined by means of one of said statistical tests (Pearson's Chi Squared test, Fisher's exact test, ...) if a variable V is sig- nificant for a cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, e.g., if the week day distribution is a priori significant in this cluster CLi. In a second step, for the most significant variable V the tags T that appear more than expected are determined. In a third step, the significance value SV for each tag T with respect to the rest of the tags T for that same variable V is determined and compared to a predefined threshold TH as de- tailed above. In this way it can be determined, e.g., if the "Saturday" distribution is significant with respect to the rest of the week in this cluster. Furthermore, an additional "sub- cluster" SCLi is generated, which only contains the rest of the traffic profiles 6 that do not correspond to the significant tags T determined before. In a fourth step, steps two and three are repeated for the sub-cluster SCLi until there are no more variables V or traffic profiles 6 to analyze. In a fifth step, the significance test for tags T is per- formed starting with the least significant variable V according to step one, but only for samples inside this sub-cluster SCLi and not with the full cluster size. If the significance value SV is above said threshold TH, those tags T will be added to the cluster label. In a sixth step, the fifth step is repeated for the next sub-cluster SCLi in increasing significance order. This time, not only its own traffic profiles 6 are considered but also the items of the previously analyzed sub-clusters SCLi that were not significant. In this way, all "significant" sub-clusters SCLi for the first level can be computed, and the corresponding tags T are added as a label to the initial cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>. If there are one or more significant sub-clusters SCLi in the first level, in a seventh step the process is repeated for each sub-cluster SCLi in the next level to determine new "child sub-clusters", considering only the characteristics or vari- ables that have not been analyzed before. These steps are then repeated until there is nothing more to analyze in any branch and all "combined" tags T can be added to the label for the child sub-clusters SCLi. Furthermore, if a sub-cluster SCLi includes more than one significant tag T for a variable V, then each tag T will be analyzed in a separate branch. Only if after analyzing all these branches they do not have sub-branches, all the tags T are grouped together. Also, to calculate the significance value SV of a tag T in each branch, only the traffic profiles 6 corresponding to the variables of all levels above the analyzed branch are consid- ered. For example, when the tag "rainy" of a sub-cluster "Fri- days" is analyzed, the expected value for "rainy" will be cal- culated considering only the weather conditions for all the "Fridays" of the total population. Returning to the second cluster CL2 of Fig. 3 detailed in Fig. 4, it can be seen that the tag combinations "Sunday and rain" and "Sunday and July" have significance values SV lying above the threshold value TH. Thus, those two tag combinations TC are assigned as characteristic vectors <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics>, <semantics>CV2<annotation encoding="application / x-tex">CV_2< / annotation>< / semantics> to the sec- ond cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>. In this example, it can be seen that while the second cluster CL2 is not representative for Sundays, rainy days, or days in July alone, this cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics> is representative for rainy Sundays and Sundays in July. Furthermore, if two clusters are assigned the same charac- teristic vectors CVi, the characteristic vector CVi whose tag T or tag combination TC has the lower significance value SV can be deleted from the label Li of this cluster CLi. By means of this, all clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> can be assigned a label Li comprising any number of characteristic vectors CVi that represent this cluster CLi. The labelling engine 14 in turn stores these labelled clusters <semantics>CLi<annotation encoding="application / x-tex">\mathrm{CL_i}< / annotation>< / semantics> in a database 16 which can again be embodied as the database 7 or a subset thereof, as the database 12 or a subset thereof, or embodied as a stand-alone database. From the first cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics> of Fig. 3 it can also be seen that since the characteristic vectors <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics>, <semantics>CV2<annotation encoding="application / x-tex">CV_2< / annotation>< / semantics>, <semantics>CV3<annotation encoding="application / x-tex">CV_3< / annotation>< / semantics>, <semantics>CV4<annotation encoding="application / x-tex">CV_4< / annotation>< / semantics> each comprise a single tag T only, they can optionally be grouped together, for example as weekdays. This can be done to reduce the number of characteristic vectors <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics>, which in turn reduces computational efforts when trying to find a certain cluster. The labelled clusters CL; in the database 16 can now be used to predict a past, present, or future traffic behaviour PTB (Fig. 2) in the road system 1. To this end, a request Req can be fed into a prediction engine 17, which for this purpose obtains the labelled clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> from the database 16. The re- quest Req comprises one or more request tags RT, which can be formulated by a user. The prediction engine 17 then matches the request tags RT to the characteristic vectors CV; of the la- belled clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> to determine a "matching" cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>. This matching cluster CLi, or any data derived therefrom, is then output by the prediction engine 17 as the predicted traffic be- haviour PTB. One exemplary setup of the engines 11, 14, 17 can be as follows: While the traffic measuring device 4 acquires data in real-time in the field, after an extended period of, e.g., one year, the clustering engine 11 and the labelling engine 14 can produce the labelled clusters CLi in the processor 9 of a cen- tral station. On the other hand, the prediction engine 17 can be embodied as an entity physically distinct from the cluster- ing and labelling engines 11, 14. Alternatively, the clustering engine 11, labelling engine 14, and prediction engine 17 can be implemented by the same machine. The operation of the prediction engine 17 is now described in further detail by means of Figs. 5 and 6. After starting the prediction process, in step 18 the cluster CLi that comprises the highest number N of traffic profiles 6 is determined and set as a reference cluster. In the example of Fig. 3, the first cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics> contains the most (N = 100) traffic profiles 6. In step 19, a dissimilarity measure D is calculated for each of the clusters CLi. The dissimilarity measure D is a measure of how much the traffic profiles 6 of a specific clus- ter CL; differ from the traffic profiles 6 of the reference cluster (here: <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics>). Once a dissimilarity measure D is calcu- lated for a cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, it can be assigned to all characteris- tic vectors CV; of this cluster CLi. Per definition, the refer- ence cluster does not differ from itself and thus has the low- est dissimilarity measure, e.g., D = 0, assigned. To compute a dissimilarity measure D for the other clus- ters, for example, an averaged traffic profile of a cluster CLi is compared to an averaged traffic profile of the reference cluster. In some embodiments, this can be done by using the same distance metric that was used to generate the clusters. In the example of Fig. 3, the third cluster <semantics>CL3<annotation encoding="application / x-tex">CL_3< / annotation>< / semantics> deviates the most from the reference cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics> and has a dissimilarity measure <semantics>D=12<annotation encoding="application / x-tex">D = 12< / annotation>< / semantics> assigned thereto. The fourth cluster <semantics>CL4<annotation encoding="application / x-tex">CL_4< / annotation>< / semantics> only deviates a little bit from the reference cluster and has a dissimilarity measure D = 3 assigned, while the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics> has a dis- similarity measure <semantics>D=7<annotation encoding="application / x-tex">D = 7< / annotation>< / semantics> assigned. It is stressed that the dis- similarity measure D is independent from the number N of traf- fic profiles 6 in a cluster CLi and only represents a differ- ence of the average, modal, or median value, or there like, of traffic profiles 6 between clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>. Any measure of (dis) similarity between curves known in the state of the art can be used as the dissimilarity measure D such as, for exam- ple, an L2 norm, an L1 norm, or hybrid norms. Steps 19 and 20 can, e.g., be performed in the processor 9 or in the labelling engine 14. After a request Req with request tags RT is fed into the prediction machine 17 in step 20, it is checked in step 21 whether all request tags RT of the request Req match one of the characteristic vectors CVi of the clusters CLi. For this pur- pose, the request tags RT can be combined to the form of a characteristic vector CV; to see if any of the characteristic vectors CV; of the clusters coincide with it. If this is the case (branch "Y"), the cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> that contains the matching characteristic vector CV; is determined as the matching cluster CLi in step 22. At the end of step 22, either the whole matching cluster CLi or an average traffic profile or any other data derived from this matching cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> can be output by the prediction engine 17 as the predicted traffic behaviour PTB for the re- quest Req. Alternatively, if in step 21 no matching character- istic vector <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> can be found amongst the clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> (branch "N"), one of the request tags RT is eliminated from the request Req in a step 23, and step 21 is repeated. The step 23 of removing a request tag RT from the request Req is described in detail by means of an example shown in Fig. 6, which again uses the exemplary clusters of Fig. 3. Here, in the beginning the request Req comprises the request tags "Wednesday", "holiday", and "rain". When the step 21 is per- formed for the first time, it is checked whether the combina- tion of these three request tags RT appears in any of the la- bels <semantics>Li<annotation encoding="application / x-tex">L_i< / annotation>< / semantics> of the four clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, see the four labels <semantics>L1<annotation encoding="application / x-tex">L_1< / annotation>< / semantics>, <semantics>L2<annotation encoding="application / x-tex">L_2< / annotation>< / semantics>, <semantics>L3<annotation encoding="application / x-tex">L_3< / annotation>< / semantics>, <semantics>L4<annotation encoding="application / x-tex">L_4< / annotation>< / semantics> on the right side of Fig. 3. In this example, no charac- teristic vector CV; can be found that comprises the three re- quest tags RT. To eliminate one of the request tags RT from the request Req, in one embodiment of the present method for each request tag RT it is checked individually whether there exists a char- acteristic vector CV; matching this request tag RT, i.e., it is not checked whether this request tag RT simply occurs in a tag combination TC of a characteristic vector CVi, but only if there is a characteristic vector CVi that exactly matches the request tag RT. By means of Figs. 3 and 6, it can be seen that the request tag "Wednesday" of the request Req occurs as the characteristic vector <semantics>CV3<annotation encoding="application / x-tex">CV_3< / annotation>< / semantics> in the label <semantics>L1<annotation encoding="application / x-tex">L_1< / annotation>< / semantics> of the first cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics>, the request tag "holiday" of the request Req occurs as the characteristic vector <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics> in the label <semantics>L2<annotation encoding="application / x-tex">L_2< / annotation>< / semantics> of the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>, and the request tag "rain" of the request Req occurs as the characteristic vector <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics> in the label <semantics>L4<annotation encoding="application / x-tex">L_4< / annotation>< / semantics> of the fourth cluster CL4. Now it is checked which of these corresponding character- istic vectors CV; has the lowest dissimilarity measure D. Since the characteristic vector <semantics>CV3<annotation encoding="application / x-tex">CV_3< / annotation>< / semantics> is in the first cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics>, which has the lowest dissimilarity measure D = 0, and the other two clusters <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>, <semantics>CL4<annotation encoding="application / x-tex">CL_4< / annotation>< / semantics> have higher dissimilarity measures <semantics>D=7<annotation encoding="application / x-tex">D = 7< / annotation>< / semantics>, 3, respectively, the request tag "Wednesday" is eliminated from the request Req because this request tag RT corresponds to a characteristic vector <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> of the cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> with the lowest dissimilarity measure D, i.e., to the least interesting cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, here: cluster <semantics>CL1<annotation encoding="application / x-tex">CL_1< / annotation>< / semantics>. Thereafter, step 21 is repeated and it is checked whether there exists a characteristic vector CVi that contains the tag combination of the remaining two request tags "holiday" and "rain". Again, this is not the case, and therefore it is again checked which of the two remaining request tags RT corresponds to a cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> with the lowest dissimilarity measure D. In this case, the request tag "rain" is eliminated from the re- quest Req because it has the lower dissimilarity measure D. Thereafter, it is again checked whether the request Req, which now only comprises the tag "holiday", matches any of the characteristic vectors <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> of the clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>. This is the case for the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>, which has the characteristic vector <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics> assigned. Therefore, the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics> is the matching cluster, from which the predicted traffic behaviour PTB is then derived. Sometimes request tags RT do not occur in a characteristic vector CV; that contains only this request tag RT in any of the clusters CLi because either this tag of the request is not pre- sent in any of the tags T of the traffic profiles 6 that are used to create the clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics> or because this tag T is only used in a characteristic vector <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> in a combination with a further tag T. In this case, the lowest dissimilarity measure, e.g., <semantics>D=0<annotation encoding="application / x-tex">D = 0< / annotation>< / semantics>, can be assigned to this request tag RT. In an alternative embodiment, when checking which of the request tags RT is to be eliminated, it is not only checked if there is a characteristic vector CVi that only comprises this request tag RT, but it is also checked whether there is a char- acteristic vector CV; comprising this request tag RT in combi- nation with a further tag T. In this case, this characteristic vector CV; and in turn the underlying cluster CL; and its dis- similarity measure D is chosen, for which, e.g., the signifi- cance value SV of the characteristic vector CV; is higher or which has a higher or lower number N of traffic profiles 6. For example, in Fig. 3 for the tag "holiday", the characteristic vector <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics> of the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics> and the characteristic vector <semantics>CV2<annotation encoding="application / x-tex">CV_2< / annotation>< / semantics> of the third cluster <semantics>CL3<annotation encoding="application / x-tex">CL_3< / annotation>< / semantics>, which has the tag combina- tion "holiday and sunny", are available. Because the signifi- cance value SV of the characteristic vector <semantics>CV2<annotation encoding="application / x-tex">CV_2< / annotation>< / semantics> of the tag com- bination "holiday and Sunday" the third cluster CL3 is higher (98%) than the significance value SV (92%) of the characteris- tic vector <semantics>CV1<annotation encoding="application / x-tex">CV_1< / annotation>< / semantics> in the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>, the dissimilarity measure D = 12 of the third cluster <semantics>CL3<annotation encoding="application / x-tex">CL_3< / annotation>< / semantics> (and not D = 7 of the second cluster <semantics>CL2<annotation encoding="application / x-tex">CL_2< / annotation>< / semantics>) is chosen for the request tag "holiday" and further used in the comparison steps of Fig. 6. Thus, in some embodiments, in which significance values SV of characteristic vectors <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> have been used to label the clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, these significance values SV can also be used when determining the cluster CLi matching the request Req. In all embodiments, when checking which request tag RT corresponds to the characteristic vector <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> of a cluster <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, and two clusters have the same characteristic vectors CV;, the characteristic vector CV; with the higher significance value SV can be chosen for this request tag RT. Furthermore, when in the matching step 21 two matching clusters CLi are found, the one with the high number N of traf- fic profiles 6 can be determined as the matching cluster and the other one discarded. To further enhance the accuracy of the method, not only can there be checked whether single request tags RT occur in the characteristic vectors <semantics>CVi<annotation encoding="application / x-tex">CV_i< / annotation>< / semantics> of the clusters <semantics>CLi<annotation encoding="application / x-tex">CL_i< / annotation>< / semantics>, but also if combinations of request tags RT correspond to a characteristic vector CVi of a cluster CLi. In this case, if this characteris- tic vector CV; corresponding to a combination of request tags RT has the lowest dissimilarity measure D amongst the charac- teristic vectors CV; corresponding to all request tags RT or request tag combinations, said request tag combination is dis- regarded until a request tag RT is eliminated from the request Req. The invention is not restricted to the specific embodi- ments described in detail herein, but encompasses all variants, combinations and modifications thereof that fall within the framework of the appended claims.

Claims

1. A method in a road system, comprising: in a traffic measuring device: measuring traffic conditions on a road or intersec- tion of roads in the form of a set of traffic profiles, each traffic profile representing a traffic measure of ve- hicles in the road system recorded over time, one or more pre-defined tags associated with a time of recording of the respective traffic profile being attributed to said traffic profile; in a clustering engine of at least one processor connected to a database, which contains said set of traffic profiles: clustering the traffic profiles with their tags into at least one cluster as to similarity of traffic profiles; in a labelling engine: calculating for at least one tag in each cluster a significance value by means of a statistical analysis, wherein the significance value of each tag or tag combina- tion, respectively, is calculated by means of a Chi- squared statistic; if the significance value of a tag is higher than a threshold value, assigning this tag as a characteristic vector to this cluster; in a prediction engine: receiving a request having one or more request tags to determine a matching cluster; determining a cluster by means of matching the re- quest tag / s to the characteristic vectors of the clusters; and outputting a predicted traffic behaviour based on the determined cluster; and - 22 - choosing at least one of a different route or a travel time for a vehicle based on the predicted traffic behaviour.

2. The method according to claim 1, wherein there are at least two variables, and each tag is assigned to a variable, the method comprising the further steps of for at least one variable in each cluster, calculating a significance value; and for at least one tag assigned to the variable with the highest significance value of each cluster, calculating the significance value.

3. The method according to claim 2, wherein the method comprises the further steps of grouping all traffic profiles that do not contain a tag whose significance value lies above said threshold value to a sub-cluster; for at least one variable in the sub-cluster, calculating a significance value; and for a tag assigned to the variable with the highest sig- nificance value of the sub-cluster, calculating the signifi- cance value.

4. The method according to claim 3, wherein the steps of grouping, calculating the significance value for a variable and calculating the significance value for a tag are repeated until no more traffic profiles are available for grouping.

5. The method according to any one of the claims 1 to 4, wherein, for at least one tag whose significance value lies below said threshold, a significance value of a combination of said tag with a further tag is calculated and, if said signif- icance value of said tag combination lies above the threshold, assigning said tag combination as a further characteristic vector to the cluster of said tag. - 23 -6. The method according to any one of the claims 1 to 5, wherein for each cluster significance values for all tags of this cluster are calculated.

7. The method according to any one of the claims 1 to 6, wherein, when two clusters would be assigned the same charac- teristic vector, the threshold value is lowered and it is again checked if the significance value of each tag or tag combination, respectively, is higher than the threshold value to assign this tag or tag combination, respectively, as a characteristic vector to this cluster.

8. The method according to any one of the claims 1 to 7, wherein the significance values of the tags or tag combina- tions are used when checking whether a request tag matches a characteristic vector.

9. The method according to any one of the claims 1 to 8, wherein each traffic profile represents the traffic measure of vehicles in the road system over a time-span of 24 hours.

10. The method according to any one of the claims 1 to 9, wherein at least one tag indicates a day of the week, a month of the year, a week of the month, a school vacation indica- tion, or a special holiday indication of said time of record- ing.

11. The method according to any one of the claims 1 to 10, wherein at least one tag indicates a road condition or a weather condition at said time of recording.