Projected Projected Arrival TimeArrival Time

Michael PaoMichael PaoMichael SmeetsMichael Smeets

Li-Ren ZhouLi-Ren Zhou

AbstractAbstractThe Projected Arrival Time (PAT) system uses the Global Positioning System (GPS) to provide accurate, real-time arrival estimates to users of a bus system. PennBus West was used for purposes of evaluating the project. Each bus carries an onboard GPS unit which transmits data to a central server running the Java 2 Platform, Enterprise Edition (J2EE) with Enterprise JavaBeans (EJB) technology. On the backend, positioning and velocity data are combined to predict arrival times, which users call via a webpage.

The PAT system adjusts to variations in weather and traffic patterns. However, conditions do arise which severely hamper the ability of buses to run on schedule, such as extreme weather and breakdown. Despite its limitations, the system is reliable to the point where it can be deployed commercially as a trustworthy convenience.

Advisors:Advisors:Siddharth DeliwalaSiddharth Deliwala

Philip FarnumPhilip Farnum

Demonstrations:Demonstrations:April 21April 21stst, 2005, 2005

RCA Lab, 1:30 – 3:30 PMRCA Lab, 1:30 – 3:30 PM

Rayming TN – 202 GPS Receiver

HP iPAQ 3815

Samsung SGH-E 105 Cell Phone

Server

PAT Website

End User End User End User

System OverviewSystem Overview

User InterfaceUser Interface

The onboard hardware components consist of the GPS receiver, the iPAQ and a mobile-phone. The position and speed of the bus are recorded on the iPAQ via the Rayming GPS Receiver. This data is then transmitted to the server over a mobile-phone connection.

On the server side, the speed and position data are then processed by the PAT Algorithm to produce a projected time of arrival. The PAT and position data are relayed to the user, along with a map generated by MapQuest.

Department of Electrical and Systems and EngineeringDepartment of Electrical and Systems and Engineering

Prediction Error vs. Zone Distance of the PAT System

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Source: 100 Samples per Zone Distance, Collected on 12/7/04, 12/17/04, 1/19/05, 1/26/05, 4/8/05

ResultsResultsThe box plot below illustrates the actual arrival time minus the estimated arrival time of data collected on PennBus West. Upper and lower quartile results satisfy the 120 second threshold requirement set at the beginning of the project. Moreover, there is an upward skew, i.e. actual arrival times lagged estimated times. This was purposely integrated into the algorithm, as it is preferable for the end user to be slightly early than to miss the bus altogether.

A web-based graphical user interface empowers users to simultaneously track a bus’s real-time location and projected arrival time. This feature also allows the user to intuitively grasp if the bus is experiencing operating problems or detect system malfunction.

(Left) Onboard hardware: receiver, iPAQ, null-modem and mobile-phone(Right) PennBus West on break

Software ArchitectureSoftware Architecture

GPS Data Event

Add GPS String to Queue

New Queue Item?

Connect to Server?

Attempt Reconnect

Transmit GPS String

Poll For Data

Parse GPS Data

Determine Zone

Insert Data

Wait For New Connection

Create New Thread

Insert Data Into DB

Retrieve DB Information

DB

Bus Thread

Interface

Data Access Bean

Server

Shared Object Yes

No

No

YesTCP/IP

PDA

PAT AlgorithmPAT AlgorithmPennBus West serves West Philadelphia between the intersections of 33rd and Walnut and 48th and Baltimore. This route has been divided into 28 regions. Distance between the bus and desired stop is calculated by summing the distances between the current regions of the vehicle and desired stop. Arrival time is projected by dividing distance by the average velocity of the last 120 samples, adjusted by a scaling factor based on the current position of the bus.