  The deployment of smart-card-based public transit fare payment systems
provides government the opportunity to create a valuable derivative data
product. Companies such as Urban Engines have demonstrated an ability to add
value to the data derived from transit fare transactions. The challenge for the
public sector is to, for the societal good, leverage private sector interest by
giving access to useful fare transaction data in a manner that protects
customer privacy. This challenge is particularly acute in California, where
privacy laws make sharing data in a manner that supports the public interest
difficult. This paper presents the Metropolitan Transportation Commission's
(MTC's) proposed solution to the problem. MTC operates the Clipper(r) transit
fare payment system for the San Francisco Bay Area. In an effort to share
usable data that protects customer privacy, MTC developed an anonymizing scheme
that is the subject of the present paper. We seek feedback on our approach from
the Data for Good Exchange community, asking: in seeking a balance between
customer privacy and usability, does the scheme go too far in either direction?
And, should we take a different anonymizing approach?
