This invention was not made pursuant to any federally-sponsored research and/or development.
The present invention relates to a method and system for assisting the drivers of vehicles, and the intelligent in-vehicle systems in partially or fully automated vehicles, to select a specific lane for vehicle travel on limited access highways, as well as a recommended vehicle speed.
Motorists driving conventional vehicles on freeways typically use visual information on their surroundings, together with whatever traffic related information that might be available, to select driving lanes and target speeds. In partially automated vehicles, this information may be enhanced by sensors located on the vehicle. Fully automated vehicles primarily use vehicle based sensor information to collect nearby status information and employ interpretative algorithms to convert this information to lane and speed choices.
In recent years, the increase in traffic levels along with difficulties with the construction of new freeway facilities has resulted in strategies that manage lane use. These strategies include the preferential assignment of classes of vehicles to specific lanes and the use of aggressive tolling strategies. In some cases, these strategies are lane specific and may vary with time-of day or with traffic conditions.
An additional set of strategies (that may also be traffic responsive or that may vary with time of day) termed “active traffic management” also limit and control the use of lanes. These strategies have been employed in Europe for some time (see Fuhs, C., Synthesis of Active Traffic Management Experiences in Europe and the United States, FHWA Report No. FHWA-HOP-10-031, May, 2010) and are being increasingly emphasized by intelligent transportation systems in the U.S. Table 1 shows the strategies that constitute this set.
Motorists are traditionally informed about lane selection associated with these strategies by dynamic message signs (DMS) also called variable message signs (VMS), by lane control signals (LCS) and by changeable speed limit signs controlled from a transportation management center (TMC). The driver uses this information, together with preferences that he may have and constraints imposed by the vehicle that he is driving, to select the appropriate lane and speed.
There have recently been significant developments in the development of automated vehicles. Levels of automation have been classified as follows by two agencies as shown in Table 2.
The following discussion employs the U.S. classification system.
Automated vehicles at levels 2 through 4 generally provide two capabilities:
With the rapid improvement in implementing technology at Levels 2-4, the emphasis being placed on its implementation by auto manufacturers and others, the adoption of some form of authorization by three states (see Kelly, R. and M. Johnson, Legal Brief, Thinking Highways, North American Edition, October, 2012), it has been estimated that significant operational use may be achieved in ten to twelve years (see Self-Driving Cars: The Next Revolution, KPMG and the Center for Automotive Research).
At Levels 0 and 1, the functions of lane and speed selection are adequately performed by the driver. Research (Redelmeier, D. A. and R. J. Tibshirani, Are Those Other Drivers Really Going Faster?, Chance, Vol. 13, NO. 3, 2000) has shown, however, that drivers often incorrectly perceive that adjacent lanes are moving faster and are thus motivated to change lanes unproductively. This results in needless fuel consumption and a crash rate that is higher than otherwise would be the case. Guidance to the motorist on when a lane change would be appropriate will contribute to a smoother, safer ride with reduced fuel consumption. The Automated Lane Management Assist (“ALMA”) concept disclosed in the present application provides this capability.
As the intent of levels 2 to 4 is to reduce, and ultimately eliminate the driver's real time participation in vehicle operation and management, a scheme to coordinate these decisions with the current limited access highway lane use and speed limit requirements as well as with the characteristics of the vehicle and the general preferences of the driver is required.
Conceptually, ALMA may be viewed as a level of decision software that lies between the vehicle's navigation function (position determination and route selection) and the lateral and longitudinal control functions as shown in
The ALMA concept converts information from freeway transportation management centers or Traffic Management Centers (“TMCs”) operated by states and other agencies to a form that assists in the selection of driving lanes and selection of target speeds for vehicles. Although providing general road congestion information is well-known in the art, the use of specific lane status information on a multi-lane limited-access highway has not been used for assisting the driver or in an automated vehicle—for selecting a travel lane and the travel speed in that lane. In fact, the lane congestion or driving condition information on specific, short geographic roadway segments has not been used to assist the drivers, or the intelligent in-vehicle systems (in partially and fully automated vehicles), select the lane and the travel speed in that lane.
The ALMA Management Center (ALMAMC) obtains information on lane traffic conditions, lane use restrictions and speed limits from the TMCs, processes it to compute appropriate traffic parameters and reformats it to formats required by ALMA data structures. It also manages the static ALMA database. This information is communicated to the vehicle by a suitable means. Satellite radio and cellular telephone are examples of communication schemes. While ALMA can potentially use infrastructure-to-vehicle communications developed under the USDOT connected vehicle program, ALMA does not depend on the availability of communications that may be provided by that program.
The dashed rectangles enclosed by
The Guidance Assist Vehicle Module (GAVM) employs the ALMA developed information to implement or assist in the implementation of mandatory and optional lane changes and the development of a target speed for the selected lane. The algorithms and logic for the GAVM are developed by the vehicle supplier (OEM) or other parties using ALMA provided data and ALMA data structures along with other data as shown In
It is an object of the present invention to achieve, provide, and facilitate:
These and other strategies are accomplished by obtaining the real-time or near-real-time information from the TMCs and using that data to make or supplement vehicle lane control decisions, further enhancing the vehicle control process. The decisions and communication to the vehicles are done in real-time or near-real-time.
More specifically, the vehicle control will not only be determined based on direct external parameters such as those provided by the sensors on the vehicle and/or by vehicle-to-vehicle communications, but also by the data collected and processed by the TMCs from its own vehicle detectors, cameras, incident reports, scheduled roadway closures and TMC operator input. Additionally, the vehicle's operator may put in some information about the vehicle's characteristics, passenger occupancy and willingness to take highways, pay tolls, and other driving preferences.
The present invention differs from prior art references that provide lane selection and speed guidance in that the prior references are oriented towards conventionally-driven vehicles. The present invention is intended for use in conventionally driven vehicles, partially automated vehicles, and fully automated vehicles. As the level of automated driving increases, the need for greater precision in providing this guidance also increases because of reduced emphasis on driver input. These increases in precision include tighter geometric boundaries for which the information is provided as well as the increasing imposition of constraints on lane use inferred by traffic management authorities. The present invention includes the following features:
These features, aspects and advantages of the novel Management Center Module For Advanced Lane Management Assist will become further understood with reference to the following description and accompanying drawings where
Active traffic management is an ITS technology that has found considerable use in Europe and is beginning to be used in the U.S. It brings traffic responsive control to the lane level by providing information to the motorist on the use lanes and speed limits associated with the lanes. These lane uses and speed limits uses may change as a function of time, traffic conditions or the location of incidents. The motorist is normally provided with this information by means of changeable message signs, lane use controls signals and variable speed limit signs.
In recent years, other lane management strategies including high occupancy vehicle lanes, high occupancy toll lanes and time variable toll pricing have become common, and variable speed limits are expected to become more commonly employed. While motorists driving conventional vehicles respond to this these requirements in a conventional way, the anticipated use of self driving vehicles or vehicles providing the driver with a considerable level of safety assists may require help in selecting the appropriate lane and adjusting the vehicle target speed to appropriate levels. This document terms such vehicles “automated vehicles” with the understanding that there may be varying levels of automation.
Advanced Lane Management Assist (ALMA) provides the vehicle with information that enables it to adapt to the requirements of the issues described above. It enables control information developed in freeway traffic management centers to be used together with information provided by the vehicle and vehicle operator. This information enables limited access highway lane control recommendations and appropriate speed settings to be provided to vehicles. The remainder of this document describes the concepts, components and software required to develop this information.
Basic Functions.
A system and method for Advanced Lane Management Assist (ALMA) are provided. ALMA provides information to conventional and automated vehicles to enable them to respond to information from the freeway traffic management center in a way that is similar or superior to the way that an unaided human driver would respond to the information.
In addition to lane based traffic parameters this information includes:
Other constraints on lane use may apply. These may include:
The Applicant, acting as his own lexicographer, identifies the symbols and abbreviations used in this application in Appendix A attached hereto and made a part hereof.
Vehicles employing ALMA require a route development capability (navigation system). Automated vehicles employing ALMA have a system that uses vehicle based sensor information to control vehicle position and speed (vehicle control system). As shown in
Data Flow Relationships.
The ALMA Management Center (ALMAMC) obtains traffic parameters, lane use information and speed limits from Freeway Traffic Management Centers and reformats it to formats required by ALMA data structures. It also manages the static ALMA database. This information is communicated to the vehicle by a suitable means. Satellite radio, conventional radio and cellular networks, including cellular telephone and data networks, are examples of communication schemes that may be used.
The dashed rectangles enclosed by
The dash-dot enclosure in
Basic ALMA Data Structure.
An earlier patent, U.S. Pat. No. 7,030,095 (Lee), provides lane status information with no discussion of its application. That patent however, provides the information aggregated at the traffic link level (a link is a roadway section between access and/or egress points on highway). That level of aggregation is not sufficiently detailed for use by automated vehicles. Furthermore the Lee patent does not provide for the additional features required to provide lane selection and speed guidance by automated vehicles or for more accurate guidance for conventional vehicles. The ALMA data structure and the features described in this patent address these issues and provide guidance at the requisite level of detail and accuracy.
A barrel is a set of lanes in a roadway using lane management techniques. It is physically or functionally separated from other parallel lane sets. There are several types of barrels. The simplest type of barrel has traffic flow in one direction; however, contra-flow lanes may be present. Barrel boundaries are determined by changes in the physical roadway configuration and by permanent changes along the roadway in the regulatory use of the roadway or its lanes.
A barrel is divided into zones. Zone boundaries are determined by a number of factors including traffic conditions, placement of motorist information devices and regulatory devices that provide changeable information. The zone boundaries are also identical to the active traffic management control signal boundaries.
Entry zones are defined for locations adjacent to the barrel. A representation of a simple barrel with its zones is shown in
ZP(P, Barrel)={Entry zone, number of zones in path, path trace less last zone, last zone}
Thus the path set for a vehicle entering at entry zone a is
ZP(1,Barrel)={a,7,1,2,3,4,5,6,7} (1)
The path set for a vehicle entering at c is
ZP(2,Barrel)={c,4,4,5,6,7} (2)
A path set for a vehicle in a contra-flow lane is
ZP(3,Barrel)={b,7,7,6,5,4,3,2,1} (3)
Note that the last zone may also serve as an entry zone for another barrel. Depending on its destination requirements, a vehicle may exit a path prior to reaching the last zone on the path.
In some cases, an entry zone may serve more than one barrel. This may happen when a roadway divides.
An example of a reversible lane barrel is shown in
Path sets include the following:
ZP(1,Barrel)={a,5,1,2,3,4,6} (4)
ZP(2,Barrel)={c,3,4,6,8} (5)
ZP(3,Barrel)={b,6,8,7,6,5,4,2} (6)
ZP(4,Barrel)={d,4,6,5,4,3} (7)
Vehicles may exit the barrel prior to the last zone identified in the path.
A relationship is required in the vehicle (and is assumed to be provided by the vehicle) between the vehicle's planned route as established by the vehicle mapping function). It must relate the segment sequence as mapped in the vehicle's mapping system to the system's appropriate barrel, path, entry zone and exit zone.
ALMAMC Top Level Module and Processes.
ALMAMC executes its processes through software modules. With reference to
Module 1—Lane Closure Guidance
Module 2—Explicit Lane and Speed Limits Requirements from TMC
Module 3—Dynamic Lane Use Requirements
Module 4—Toll Information
Module 5—Check Traffic Data for Accuracy
Module 6—Prepare ALMA Traffic Data for Use by Vehicle
Module 7—Miscellaneous Data
ALMAMC Module Process Descriptions
Module 1—Lane Closure Guidance
The flow chart for this module is shown in
The module considers the case where two lane blocking incidents occur in adjacent lanes and in sequential zones. The processes in the flow chart provide for diversion to an unblocked lane where it is possible to do so and otherwise indicate that guidance cannot be provided.
Module 2—Explicit Lane and Speed Limit Requirements from TMC
Some TMCs provide explicit lane control and speed limit requirements. When appropriate, this module obtains this information from the TMC and provides it to the vehicle. These may be developed in the TMC by some combination of automatic and manual operation. The Module 2 Flow Chart (
2.1 Convert Lane Control Information from TMC LCS to ALMA Protocols
Module 3—Dynamic Lane Use Requirements
Module 4—Toll Information
The purpose of this module is to provide toll information to the vehicle operator through the GAVM and thence to the ODE.
The basic parameter developed by the module is {VTR(B1,Z1,B2,Z2)}. It represents the set of toll charges from the vehicle's entry point in the toll system (Barrel B1, Zone Z1) to the point at which it exits the toll system (Barrel B2, Zone Z2). A set of baseline tolls is provided in the static database. If these tolls vary with time or traffic conditions, this information will be provided to the ALMAMC by the TMC. These updates are then sent to the GAVM.
Module 5—Check Detector Data for Accuracy
Data for each lane is developed from detector speed, volume, occupancy and classification volumes. This data will originate with point traffic detectors in Freeway Management Systems (FMS).
Where the TMC does not provide sufficient data checking and imputation capability, the alternative path in
Module 6—Prepare ALMA Data
This module uses the speed, volume, occupancy and vehicle length classification data from point traffic detectors in each lane to develop the following zone parameters for communication to the Guidance Assist Vehicle Module (GAVM): zone speed, zone density, zone volume, zone passenger car equivalents, zone average headway, average vehicle length for zone.
This module performs two functions:
A Kalman filter will be used to process the SPINT(DET,L) valid speed data (valid if SPINT(DET,L)< >−1), OCCINT valid occupancy data (valid if OCCINT< >−1, VOLINT valid volume data (valid if VOLINT< >−1) to conform to a common data period such as one minute. If it is not valid, data from the prior minute will be used as the Kalman filter input. Standard Kalman filter equations will be used (see, for example Welch, G and T R Bishop, “An Introduction to the Kalman Filter”, University of North Carolina Department of Computer Science, TR 95-041, 2006). Filtered parameters include speed (SPFIL(DET,L)), filtered volume (VOLFIL(DET,L)), filtered occupancy (OCCFIL(DET,L)). If the standard deviation of the error estimate provided by the Kalman filter exceeds settings established by the ALMAMC operator, an indication (NOSPEED(DET,L), (NOOCC(DET,L), NOVOL(DET,L) will be provided for that data period. The Kalman filter's standard deviation for speed (SPDEV(DET,L) will also be provided.
Filtering techniques other than a Kalman filter may also be used. Examples of other filtering techniques include a first-order low-pass filter and a moving average.
Speed data collected from or computed from point detector data is time mean speed. It is more appropriate to use space mean speed for ALMA's purposes. The definition of these quantities and the relationship between them is provided by May (May, A. D., “Traffic Flow Fundamentals”, Prentice Hall, 1990). The relationship when solved for space mean speed, and using the Kalman filters error estimate is shown as follows:
The relationship between density and the volume and space mean speed variables is (May, op.cit.)
Gordon (Gordon, R L and Tighe, W, “Traffic Control Systems Handbook”, FHWA Report FHWA-HOP-06-006) defines occupancy as follows:
θ=Raw occupancy, in percent
T=Specified time period, in seconds
ti=Measured detector pulse presence, in seconds
LR=Ratio of the effective length of the vehicle plus the loop to the vehicle length
N=Number of vehicles detected in the time period, T
D=Detector drop out time−detector pick up time
While this definition was developed for inductive loop detectors, other detector technologies exhibit similar detection zones, but with different values for L.
The occupancy value provided by most TMCs do not provide compensation for this effect. Where this is the case, the occupancy data will be compensated for LR. This will permit the use of a mix of detection technologies from different TMCs as well as the use of detectors using different technologies in a single TMC. The relationships for compensated occupancy (COMPFILOCC) are:
For each detector station and lane,
OCCINT(Det,L)=⊖ (11)
OCCFIL(Det,L) is the corresponding Kalman filtered occupancy variable
If the data is already compensated by the TMC then
COMPFILOCC(Det,L)=OCCFIL(Det,L) (12)
If the data has not been compensated by the TMC then
COMPFIL0CC(Det,L)=OCCFIL(Det,L)/LR (13)
Some algorithms in the Guidance Assist Vehicle Module may elect to use a comparison of PCEs in adjacent lanes as a parameter for lane selection. Equivalency factors are identified for trucks and buses (ET) and for recreational vehicles (ER) in the Highway Capacity Manual (“HCM 2010”, Transportation Research Board, 2010). HCM 2010 provides these factors as a function of highway grade and the percentage of vehicles in each class.
For each data accumulation period (typically one minute) certain detectors provide a count of vehicles in each class. These are denoted as VAUTO(Det,L,p), VTRUCK(Det,L,p), VRV(Det,L,p). p is the data accumulation period.
Hourly compilations of these values are compiled and fractional values for each class are computed as follows:
If detectors do not have a classification capability, representative hourly values are obtained by manual observations of CCTV images of detector sites.
Average vehicle length is obtained as follows:
AVL(Det,L,Hr)=AVAUTOLEN*(1−FRTRUCK(Det,L,Hr)−FRVRV(Det,L,Hr))+FRTRUCK(Det,L,Hr)*AVTRUCKLEN(Det,L,Hr)+FRVRV(Det,L,Hr)*AVRVLEN (17)
Passenger car equivalents (PCE) are obtained as follows
PCE(Det,L)=VOLFIL(Det,L)*((1−FRTRUCK(Det,L)−FRVRV(Det,L)+ET*FRTRUCK(Det,L)+ER*FRVRV(Det,L)) (18)
6.2.4 Computation of Space-Mean-Speed and Density from Occupancy
Some traffic detector technologies do not measure speed at all or measure it poorly. Generally these technologies measure occupancy (the time period that the vehicle is in the detector's sensing zone). Speed and density for this class of detectors is obtained from volume and occupancy as follows.
Klein (Klein, L. A., “Sensor Technologies and Data Requirements for ITS”, Artech House, 2001) provides the following relationship between density and occupancy.
DENFIL(Det,L)=(F*OCCFIL(Det,L))/(LL+AVL(DetL)) (19)
where LL is the detector's sensing distance on the roadway and F is a coefficient. If AVL and LL are in feet, and F=5280, then DENFIL(Det,L) is in vehicles per mile per lane.
Rearranging the terms of Equation 9 provides the relationship for space-mean-speed for this case.
SPSP(Det,L)=VOLFIL(Det,L)/DENFIL(Det,L) (20)
The data developed in Modules 6.1 and 6.2 are referenced to the coordinate system employed by the TMC developing the data. Since this is most likely different from the ALMA data structure (Section 4), conversion to the ALMA data structure is required. To do this, one and only one detector station is assigned to each ALMA zone. In some cases, the zone detector station might not physically lie within the zone. When the detector error indications show that the data is unacceptable, a value of −1 is assigned to the zone variable. Some detector types have the capability to classify vehicles according to length. Zone based traffic variables are denoted by the ALMA data structure subscripts. These are B (barrel), Z (zone), L (lane).
The roadways serviced by different traffic management centers may be equipped with detectors using different technologies. The data parameters and their accuracy provided by these technologies differ depending on the technology. Table 3 identifies the traffic parameter data provided to the Guidance Assist Vehicle Module (GAVM) as well as the associated computational process. A very broad set of possible algorithms and vehicle guidance rules may be implemented in the GAVM. The ALMAMC data outputs described in this section provide the data required for this broad set.
Module 7—Miscellaneous Data
Table 4 identifies data that may vary and is therefore not included in the Static Database. It is basically obtained from the TMC, and transformed into ALMA coordinates as appropriate.
Table 5 identifies certain parameters included in the static database.
Refer to process descriptions for index referencing
This patent application is a nonprovisional application of, and claims priority to, provisional patent application Ser. No. 61/747,331 filed on Dec. 30, 2012, provisional patent application Ser. No. 61/750,426 filed on Jan. 9, 2013, and provisional patent application Ser. No. 61/827,067 filed on May 24, 2013, all of which are hereby incorporated by reference in their entirety.
Number | Date | Country | |
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61747331 | Dec 2012 | US | |
61750426 | Jan 2013 | US | |
61827067 | May 2013 | US |