Patent Publication Number: US-9836979-B2

Title: Method and system for latent demand modeling for a transportation system

Description:
BACKGROUND 
     The present disclosure relates to modeling demand in a transportation system, such as a public bus, train or plane system. More specifically, the present disclosure relates to latent demand modeling as a function of the time of the day and the day of the week for a transportation system. 
     Many service providers monitor and analyze analytics related to the services they provide. One important analytic related to efficient operation is travel demand for a transportation system or a particular route in a transportation system. For example, public transportation vehicles may be equipped with an automated passenger counter configured to measure passengers boarding or alighting a vehicle at a particular stop. However, data from automated passenger counters is not collected regularly, and thus the information is difficult to accurately correlate to time and place. Additionally, if no one is at a stop, the vehicle typically will not stop unless there is a passenger wanting to get off the vehicle. Thus, such stops may be ignored completely and there is no registration of the stop with the automated passenger counter. 
     Additionally, public transportation vehicle routes are run irregularly throughout the day, and some routes are not run at all at certain hours such as late at night or early in the morning, e.g. from 2:00 AM to 5:00 AM. Thus, the actual number of passengers picked up at a stop, i.e., the demand at that stop, is not only dependent upon the time of the day but also the interval between vehicles servicing that stop. A longer interval will result in a higher number of passengers. However, this increase in passengers may not be related to the population or overall demand of the stop. Rather, the increase may be a result of a longer time interval between vehicles servicing that particular stop. As such, using existing technology and techniques to estimate demand results provides an incomplete analysis when modeling demand as a function of time of day and day of week. 
     SUMMARY 
     In one general respect, the embodiments disclose a method of identifying demand in a transportation system. The method includes determining a boarding count model based upon passenger arrival information and determining a geographic and time-specific generalized boarding model based upon the boarding count model as well as information related to a plurality of stops on a route in the transportation system. For each of the plurality of stops, the method includes determining an approximated uniform arrival model based upon the generalized arrival model and a time period between arriving vehicles at a specific stop, determining an instantaneous demand model based upon the uniform arrival model, and determining a probability of no demand model based upon the uniform arrival model. The method also includes generating a report including at least an indication of instantaneous demand determined based upon the instantaneous demand model and an indication of probability of no demand determined based upon the no demand model, and presenting the report. 
     In another general respect, the embodiments disclose a system for identifying demand in a transportation system. The system includes a processing device, a display device operably connected to the processing device, and a computer readable medium in communication with the processing device. The computer readable medium includes one or more programming instructions for causing the processing device to determine a boarding count model based upon passenger arrival information and determine a geographic and time-specific generalized boarding model based upon the boarding count model as well as information related to a plurality of stops on a route in the transportation system. For each of the plurality of stops, the one or more instructions cause the processing device to determine an approximated uniform arrival model based upon the generalized arrival model and a time period between arriving vehicles at a specific stop, determine an instantaneous demand model based upon the uniform arrival model, and determine a probability of no demand model based upon the uniform arrival model. The one or more instructions further cause the processing device to generate a report that includes an indication of instantaneous demand determined based upon the instantaneous demand model and an indication of probability of no demand determined based upon the no demand model, and display the report on the display device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a sample flow chart for modeling demand for a transportation system according to an embodiment. 
         FIG. 2  depicts an example of a plot of observed and estimated passengers boarding for a particular transportation route according to an embodiment. 
         FIG. 3A  depicts a level plot illustrating estimated demand at a stop on a transportation system as a function of hour and day of week according to an embodiment. 
         FIG. 3B  depicts a level plot illustrating a probability of zero demand for a stop on a transportation system according to an embodiment. 
         FIG. 4  depicts various embodiments of a computing device for implementing the various methods and processes described herein. 
     
    
    
     DETAILED DESCRIPTION 
     This disclosure is not limited to the particular systems, devices and methods described, as these may vary. The terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope. 
     As used in this document, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Nothing in this disclosure is to be construed as an admission that the embodiments described in this disclosure are not entitled to antedate such disclosure by virtue of prior invention. As used in this document, the term “comprising” means “including, but not limited to.” 
     As used herein, a “computing device” or “processing device” refers to a device that processes data in order to perform one or more functions. A computing device may include any processor-based device such as, for example, a server, a personal computer, a personal digital assistant, a web-enabled phone, a smart terminal, a dumb terminal and/or other electronic device capable of communicating in a networked environment. A computing device or processing device may interpret and execute instructions. Unless specifically limited, reference to any device can refer to a single device and/or a group of devices which work together to implement a process. 
     A “mathematical model,” or simply “model,” refers to a process of developing a mathematical representation of one more variables and one or more relationships that exists between those variables. A variable, as used herein, refers to abstractions of quantifiable parameters of interest that are either known or are being solved for in the model. A relationship, as used herein, refers to algebraic operators, functions and algorithms and other similar mathematical operators. 
     The present disclosure is directed to a method and system for modeling demand for a transportation system using Bayesian latent modeling techniques. Based upon information collected and modeling for a particular route or stop in the transportation system, instantaneous demand for that stop or route can be modeled for a particular time of day and day of week, as well as the probability of no demand occurring at any particular time of day and day of week. Using the techniques as described herein, a public transportation company can monitor demand at each stop along its provided routes to determine if, for example, stops should be eliminated, additional stops should be added, vehicle sizes can be adjusted, and other similar actions that can impact system efficiency and reduce and/or maximize operating expenses. 
       FIG. 1  illustrates a flow chart showing a sample process for modeling demand for a particular transportation system. For discussion purposes only, a public transportation system including multiple buses operating on varying routes, each route include multiple stops will be described. However, it should be noted that such a transportation system is described by way of example only. The processes, systems and methods as taught herein may be applied to any environment where performance based metrics and information are collected for later analysis, and provided services may be altered accordingly based upon the collected information to improve demand-based efficiency. 
     As shown in  FIG. 1 , a computing device may determine  102  a current boarding count model for a particular stop in the public transportation system. Passenger information can be obtained from an automatic passenger counter device associated with each vehicle in the transportation system. Inspection of typical passenger data for a public transportation system may show fairly sparse demand at certain times of the day. For example, near a city, public transportation demand is greatest at rush hours (e.g., 7:00-10:00 AM and 4:00-7:00 PM). At times outside of the rush hour ranges, demand can be reduced to near zero. As such, determining  102  a current boarding count model for a particular stop may be done using a zero inflated Poisson distribution, i.e., a distribution that provides for frequent zero-valued observations. In this case, the processing device may determine  102  the current boarding model using the following equation:
 
 f ( x; p , λ)= pI ( x =0)+(1 −p )Pois( x ,λ)  (1)
 
where x is the number of passengers boarding the vehicle at a given time interval. Demand is thus determined as a rate of passengers boarding as a function of time. For example, the demand can be modeled as a Poisson arrival process that is conditioned on a latent variable of non-zero demand.
 
     However, in a typical public transportation system, different routes exhibit different demand rates as a function of geography. For example, stops located closer to higher population centers are expected to exhibit a higher demand than stops located in rural or sparsely populated areas. To account for such variation, the processing device may generalize  104  the current boarding count model for a particular route using the following equation:
 
 f ( x;p,λ   i )= pI ( x =0)+(1− p )Pois( x,λ   i ),  i= 1, . . . ,  n   (2)
 
where n is the number of stops along a particular route. Thus, the processing device can generalize  104  the boarding count model to produce a generalized boarding model accounting for each stop along a route or, more generally, each stop serviced by the transportation system, thus accounting for the geographic impact on demand throughout the transportation system.
 
     Additionally, beyond merely accounting for geographic impact on demand, the time of the day, as well as the time between scheduled stops, can impact demand. In particular, the longer the time interval between a vehicle arriving at a particular stop, the larger the resulting demand will be at the stop. In practice, arrival rates increase closer to the scheduled vehicle arrival time. However, for modeling, uniform arrival over the time interval can serve as an accurate approximation. Thus, the computing device may determine  106  an approximated uniform arrival model based upon the generalized boarding model using the following equation:
 
 f ( x;p   (t     j     −t     j-1     ) ,λ i ( t   j   −t   j-1 ))= p   (t     j     −t     j-1     )   I ( x= 0)+(1− p   (t     j     −t     j- 1     ) )Pois( x,λ   i ( t   j   −t   j-1 )),  i= 1, . . . , n; j= 1, . . . , T   (3)
 
where T represents the total time interval between scheduled arrivals at each particular stop.
 
     Thus, the current equations model a Poisson distribution of demand that varies by time and the geography of a stop. Additionally, the equations include an assumption that a latent probability of no demand varies over time to absorb the zero values of no one being at the bus stop at a given time. Zero values may be both a result of the automatic passenger counter registering a zero count at a stop (i.e., the vehicle only stopped to allow passengers to depart) as well as a non-count for a stop (i.e., the vehicle did not stop as there were no passengers wishing to board or depart). In this sense, the lack of demand can be accurately modeled to expose true demand where people may or may not use the transportation system (e.g., catch a bus) at that place and time (e.g., a particular time during a specific day). 
     To gain further insight from the data, additional explanatory variables may be introduced in the form of random effect terms for both the hour of the day and day of the week. Such an introduction can allow for insight into how instantaneous demand λ i  and the probability of no demand p (t     j     −t     j-1     )  vary by the hour of the day and the day of the week. This provides for a modeling process where a significant amount of variation is explained and accounted for. 
     The statistical model of the demand information may be fitted using Bayesian methods and may incorporate an observation process, i.e., the model compensates for the possibility that passenger arrival information from the automatic passenger counter may include errors. An example of the model may be:
 
 N   j ˜Poisson((1− u   j )λ j ( t   j   −t   j-1 ))
 
 u   j ˜Bernoulli( p   j )
 
λ j =exp( a[h ( t   j )]+ b[w ( t   j )])
 
 p   j =1/(1+exp(− c[h ( t   j )]− d[w ( t   j )])))
 
 Y   j ˜Normal((1− u   j ) N   j ,τ)  (4)
 
     In the above model, Y j  is the count of passengers at bus stop i between times t j-1  and t j ; p j  is the probability of no one even wanting to ride the vehicle between times t j-1  and t j ; h is a function that returns the hour of a time in integers from 1 to 20 (e.g., assuming that there are 4 morning hours in which the transportation system does not operate); w is a function that returns the weekday of a time in integers from 1 to 7; a and b are 20×7 matrices that captures the interactions of hour and weekday, which are estimated from the data (again, limited to 20 in this example as it is assumed the transportation system operates 20 hours a day); c and d are similar 20×7 matrices that captures the interactions of hour and weekday, which are estimated from the data; τ is the precision of the counting system by measuring the random variation not explained by the time varying model. 
     Additionally, as modeled, N j  represents a listing of the number of passengers without accounting for error and u j  represents whether a person is actually waiting at a stop or not at a given time. Thus, as modeled, the passenger count Y j  for each stop accounts for any error generated by the automatic passenger counters by including both u j  and τ. 
     Additionally, based upon the data provided for and the models included above in equation set (4), a computing device can model  108  the instantaneous demand for a stop λ i  as well as model  110  the probability p j  that there is no demand at the stop, i.e., no passengers are waiting to board at that stop at a specific time. More specifically, the computing device can model  108  the instantaneous demand λ i  as a function of the expected rate of passenger arrival over time for each hour of the day and each day of the week. Similarly, the computing device can model  110  the probability p j  of no demand as an inverse function of the expected rate of passenger arrival for each hour of the day and each day of the week. 
     In an example, the statistical models may be fit using a Bayesian fitting method such as a Markov Chain Monte Carlo method. Markov Chain Monte Carlo methods represent a class of algorithms for sampling from probability distributions based upon constructing a Markov Chain, i.e., a data structure where a current state is dependent only upon itself, not any previous states of the data. Such a data structure is applicable to modeling demand as the demand for a particular time period may be based solely upon the time of day and the day of the week for that period, and be may be completely independent of any surrounding periods. More specifically, the demand at a stop in a transportation system between 9:00 and 10:00 can be completely independent of the demand at that stop between 8:00 and 9:00 as well as between 10:00 and 11:00. 
     The computing device may generate  112  a report including the specific demand information. The report may include, for example, a representation or indication of the instantaneous demand model as determined from the instantaneous demand model for a particular stop, a representation or indication of the probability that there is no demand as determined based upon the probability of no demand model for the particular stop, as well as additional information such as estimated and actual passenger arrival information for the stop. The report may be distributed or otherwise presented to one or more recipients for further analysis and review. For example, a scheduling manager for a public transportation system may analyze both the instantaneous demand model for a stop as well as the probability for no demand model at that stop, and determine whether to eliminate that stop from the route at one or more times of the day or days of the week. Similarly, if the instantaneous demand model indicates high demand for a stop, the scheduling manager may increase the number of vehicles stopping at that stop or provide larger vehicles at that stop to accommodate the increased demand. 
     It should be noted that the computing device that performed the various model determinations may generate  112  and provide the report. However, this is shown by way of example, and additional computing devices may generate the report. For example, a manager may access a reporting application at their personal computing device. The personal computing device may access a central server, requesting the various demand models as described above. The personal computing device, via the reporting application or another similar software application, may then generate the reports for review by the manager. 
     In addition to generating a report, the system may be configured to perform additional automated operations related to the overall operation of the transportation system. For example, the system may analyze the overall demand data to adjust one or more particular routes by eliminating stops, creating new stops, and consolidating stops to smooth out demand over time. The system may automatically revise and update a route schedule, notifying a dispatcher for the transportation system that the route changes have been made to accommodate demand. Similarly, the demand information may be used by the system to automatically adjust fares during periods of varying demand. For example, during low demand periods the system may automatically lower fares to boost demand. Conversely, during high demand periods, the system may maintain a higher fare to maximize income. Additionally, the demand information may be used to automatically determine what type of vehicle to use during specific times of the day. For example, during low demand periods, the system may schedule a lower capacity vehicle to handle the lower demand, e.g., a 15-20 seat paratransit vehicle. Conversely, during high demand periods, the system may schedule a higher capacity vehicle such as a large, articulate bus to handle higher demand. 
     Additionally, the information contained within the report may be analyzed to identify and/or anticipate random high demand periods, and to respond accordingly. For example, the system may automatically deploy another vehicle to handle a random period of high demand by contacting a dispatcher or a manager in the transportation system, identifying the particular area of high demand as well as the instruction to deploy another vehicle. 
     It should be noted that while buses and similar transportation vehicles are described above, the system is not limited to transportation systems that include buses only. Airlines can utilize the automated demand monitoring techniques as described herein to modify plane schedules to accommodate passenger demand. Similarly, transportation systems including trains can use the automated demand monitoring techniques to accommodate for changes in demand as well, by alternating schedules or changing the types of trains used during certain periods of the day. For example, one or more passenger cars can be added to a train during high demand to accommodate additional riders and maximize potential income. Conversely, during periods of lower demand, one or more passenger cars can be removed from the trains, thereby reducing operating expenses during those times. 
       FIGS. 2, 3A and 3B  illustrate various components that may be included in an example report as described above. For example, as shown in  FIG. 2 , the report may include a plot of observed and estimated passengers boarding as modeled by the boarding count model. This information can be used to determine how accurate the boarding count model is with regard to a particular stop being analyzed. 
     As shown in  FIG. 3A , the representation or indication of the instantaneous demand for a particular stop can be illustrated as a level plot having the hour of the day on the x-axis, and the day of the week on the y-axis. Such a plot as that shown in  FIG. 3A  can provide a quick visual indication of the instantaneous demand model, providing a scheduling manager or other related personnel a quick indication of demand at the stop. 
     For example, as shown in  FIG. 3A , the instantaneous demand at Tuesday between 6:00 and 7:00 is about 30 people. Conversely, the instantaneous demand at Sunday between 20:00 and 21:00 is less than 10 people. Based upon this information, the scheduling manager or other related personnel can make informed decisions as to whether service to a stop should be increased or decreased at particular times. 
     Similarly, as shown in  FIG. 3B , the representation or indication of the probability of no demand for a particular stop can be illustrated as a level plot with hour of the day on the x-axis, and the day of the week on the y-axis. Such a plot as that shown in  FIG. 3B  can provide a quick visual indication of the probability of there being no demand at a stop, providing a scheduling manager or other related personnel a quick indication of when demand for a stop is at its highest and, conversely, when demand for a stop is at its lowest. 
     For example, as shown in  FIG. 3B , the instantaneous demand at Tuesday around 19:00 is about 0.7, indicating there is a high probability of there being no demand at the stop. Conversely, the instantaneous demand on Monday between 7:00 and 18:00 is less close to zero, indicating there is a very low probability of there being no demand during those times. Based upon this information, the scheduling manager or other related personnel can make informed decisions as to whether a stop can be eliminated at particular times without impacting or inconveniencing a large number of people. 
     It should be noted that, as described above, the transportation system may only operate a set number of hours a day. In the example illustrated in  FIGS. 3A and 3B , the transportation system does not operate between 1:00 and 5:00 and, thus, those times are not illustrated in the plots. 
     The processes as described herein, including the model generations, calculations and derivations as described above, may be performed and implemented by one or more operators of one or more computing devices located at an operations center (e.g., a central operations center for a public transportation provider). Alternatively, the processes as described herein may be performed automatically by one or more computing devices. 
       FIG. 4  depicts a block diagram of internal hardware that may be used to contain or implement the various computer processes and systems as discussed above. An electrical bus  400  serves as the main information highway interconnecting the other illustrated components of the hardware. CPU  405  is the central processing unit of the system, performing calculations and logic operations required to execute a program. CPU  405 , alone or in conjunction with one or more of the other elements disclosed in  FIG. 4 , is a processing device, computing device or processor as such terms are used within this disclosure. Read only memory (ROM)  410  and random access memory (RAM)  415  constitute examples of memory devices. 
     A controller  420  interfaces with one or more optional memory devices  425  to the system bus  400 . These memory devices  425  may include, for example, an external or internal DVD drive, a CD ROM drive, a hard drive, flash memory, a USB drive or the like. As indicated previously, these various drives and controllers are optional devices. Additionally, the memory devices  425  may be configured to include individual files for storing any software modules or instructions, auxiliary data, incident data, common files for storing groups of contingency tables and/or regression models, or one or more databases for storing the information as discussed above. 
     Program instructions, software or interactive modules for performing any of the functional steps associated with the processes as described above may be stored in the ROM  410  and/or the RAM  415 . Optionally, the program instructions may be stored on a tangible computer readable medium such as a compact disk, a digital disk, flash memory, a memory card, a USB drive, an optical disc storage medium, a distributed computer storage platform such as a cloud-based architecture, and/or other recording medium 
     An optional display interface  430  may permit information from the bus  400  to be displayed on the display  435  in audio, visual, graphic or alphanumeric format. Communication with external devices may occur using various communication ports  440 . A communication port  440  may be attached to a communications network, such as the Internet or a local area network. 
     The hardware may also include an interface  445  which allows for receipt of data from input devices such as a keyboard  450  or other input device  455  such as a mouse, a joystick, a touch screen, a remote control, a pointing device, a video input device and/or an audio input device. 
     Various of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments.