Communications: electrical – Vehicle detectors – Density
Reexamination Certificate
1999-08-16
2001-12-11
Wu, Daniel J. (Department: 2632)
Communications: electrical
Vehicle detectors
Density
C340S936000, C701S119000
Reexamination Certificate
active
06329932
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for determining traffic data, and to a traffic information center.
2. Discussion of the Prior Art
Methods exist for automatically producing traffic reports by assessing point-related data from stationary vehicle detectors, such as induction loops, in order to assess the traffic situation at or in the vicinity of the stationary detectors. In this case, data detected by a plurality of stationary detectors along, for example, a road section are collated in a center to form messages such as “three kilometer traffic jam between X
18
and X
2
”.
With regard to optimization of this system by determining traffic data on the basis of measurements from stationary detectors and mobile detectors (that is to say detectors which are also moving in the traffic), it is problematic that data from the two types,of detector are transmitted only at relatively long time intervals as a result of the telecommunications costs incurred for transmission to a center and that, owing to the limited number of stationary and mobile detectors, the data are transmitted only at relatively long distance intervals. Furthermore, and in particular, the data supplied from these two data sources and relating to vehicle speeds differ since, for example, the mean speed of travel of this one vehicle in this time interval along a path travelled by this vehicle is transmitted by vehicles to a center after a time interval in each case, while the mean vehicle speed of a large number of vehicles passing a specific point in the traffic system, namely the location of the detector, is transmitted by a stationary detector to the center within a time interval which is, furthermore, often relatively short. Separate treatment of single-point-related data (originating from stationary detectors) and distance-related data (originating from mobile detectors) results in inaccurate and inconsistent reports relating to the traffic situation.
Existing approaches to determining traffic data, in particular traffic jam reports, on the basis of speed measurements from stationary detectors and from mobile detectors, namely traffic flow models, domain models, microscopic models, are highly complex and have not been tested much in practice; in addition, some of these existing methods require a certain amount of input data synchronism.
SUMMARY OF THE INVENTION
The object of the invention is therefore to provide a method which is as simple and efficient as possible for determining traffic data at points of interest in a traffic system, taking account not only of vehicle data which respectively relate to the mean speed of one vehicle but also of stationary detector data which relate to the mean speed of a number of vehicles at one stationary detector.
Traffic data to be determined in the sense of the invention may, in particular, be mean vehicle speeds at points of interest in a traffic system and/or traffic jam indicators (free, slow moving, very slow moving, traffic jam) determined from these speeds and, possibly, from other additional information. Points of interest in a traffic system may, in particular, be points where vehicle drivers wish to have data relating to the traffic situation there, in particular traffic jam indicators; furthermore, points of interest may be junctions, ramps, intersections and/or ends of road segments of a road on a digital map. If no up-to-date FCD data are available at a point, interpolation can be carried out from data from at least two stationary detectors. If only FCD data are available at a point, FCD data can be interpolated from at least two vehicles. At at least some points, the interpolation is carried out on the basis of data from at least one vehicle and data from at least one stationary detector, possibly from a plurality in each case. In addition, it is possible to determine traffic data, in particular the traffic jam situation, at a large number of points defined, for example, in a close grid, and to transmit to vehicle drivers only significant traffic data such as traffic jams which are building up, are in existence or are clearing. The calculation of vehicle speeds, in particular of mean vehicle speeds, at each point of interest is expediently carried out by means of a program running in a computer in a traffic information center.
When calculating mean vehicle speeds at points of interest, the vehicle detector data and/or stationary detector data may be weighted. The weighting can be carried out from values based on experience. The quality of the results of the method can thus be optimized.
According to one refinement of the invention, the speed at the current point in time at each one point of interest is determined by linear interpolation of two speed values, which are adjacent in terms of position and/or time, from stationary detector data and/or from vehicle data. Interpolation from more than two speed values is also possible. Linear interpolation of speeds v(x, t) is the simplest form of interpolation to carry out by computer and results in relatively low errors. In contrast, higher-order interpolation processes take more computation time and provide only slightly better results.
With regard to the interpolation of speeds v(x, t), it is expedient also to take account of additional information, in particular information relating to roadworks and/or the proportion of trucks on road segments and/or traffic flows in specific traffic lanes, which likewise optimizes the quality of the results of the method according to the invention.
The association of vehicle data (that is to say data transmitted from one vehicle in each case, that is to say FCD) with defined points is preferably carried out by definition of the speed (which in each case represents one vehicle in vehicle data) as the speed of that vehicle at a defined point such as, in particular, at a position in the road segment at which the vehicle is currently located. This position may be, in particular, the start, middle or end or the like of the current road segment on a digital map of the traffic system in a computer in the center. This reduces the accuracy only to a relatively minor extent. However, it allows simple and efficient conversion of distance-related FCD data to singlepoint-related data, and thus joint analysis of vehicle data (FCD) and stationary detector data.
On the basis of the measured traffic data and the traffic data determined according to the invention, in particular speeds at a large number of points of interest with measurement data or interpolated data for a traffic system, a traffic jam indicator (free, slow moving, very slow moving, traffic jam etc.) is expediently assigned to these points in the traffic system on the basis of the vehicle speeds measured or calculated for these points of interest. This traffic jam indicator is even more suitable for assessing the traffic jam situation and for transmission to those in the traffic as mean speeds at a large number of points.
Furthermore, traffic information (“traffic jam between A and B on the A
8
” or the like), in particular in traffic jam reports, relating to traffic system segments is expediently determined and issued on the basis of a number of traffic jam indicators (such as 1. “traffic jam at A on the A
8
” and 2. “traffic jam at B on the A
8
” and, possibly, other local traffic jam indicators at other points of interest) which are, in particular, associated in terms of position with these traffic system segments. The traffic information which can be transmitted to those in the traffic is thus compressed. Only traffic information (such as traffic jams) which is assessed as being important on the basis of criteria which can be predetermined is preferably in this case issued by the program in the center.
The time interval within which a vehicle determines its own mean speed is expediently longer than the time interval within which the speeds of vehicles passing a stationary detector are in each case measured and averaged by this stationary detector. This results in further pract
Cohen & Pontani, Lieberman & Pavane
Huang Sihong
Mannesmann AG
Wu Daniel J.
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