  Understanding the quality and usage of public transportation resources is
important for schedule optimization and resource allocation. Ridership and
adherence are the two main dimensions for evaluating the quality of service.
Using Automatic Vehicle Location (AVL), Automatic Passenger Count (APC), and
Global Positioning System (GPS) data, ridership data and adherence data of
public transportation can be collected. In this paper, we discuss the
development of a visualization tool for exploring public transportation data.
We introduce "map view" and "route view" to help users locate stops in the
context of geography and route information. To visualize ridership and
adherence information over several years, we introduce "calendar view" - a
miniaturized calendar that provides an overview of data where users can
interactively select specific days to explore individual trips and stops ("trip
subview" and "stop subview"). MetroViz was evaluated via a series of usability
tests that included researchers from the Center for Advanced Transportation
Technology (CATT) and students from the University of Maryland - College Park
in which test participants used the tool to explore three years of bus transit
data from Blacksburg, Virginia.
