The National Academies

NCHRP 08-36/Task 136 [Completed]

License Plate Reader Technology: Privacy Risk Analysis and Case Studies
[ NCHRP 08-36 (Research for the AASHTO Standing Committee on Planning) ]

  Project Data
Funds: $125,000
Research Agency: Cambridge Systematics, Inc.
Principal Investigator: Johanna Zmud
Effective Date: 9/11/2015
Completion Date: 11/15/2016



Technological advances have enabled new methods of collecting transportation data. Interest in automated license plate reading (LPR) technologies is increasing because of the wide range of applications to which they can be applied.  LPR is an image-processing technology used to identify vehicles by their license plates. LPR systems use cameras, computer hardware, and software to capture an image of a license plate, recognize its characters by converting them into readable text, and check the license plate against designated databases for identification. Typically, LPR systems are used for enforcement and data collection applications including parking lot management, origin-destination studies, traffic flow studies, high occupancy vehicle analysis, weigh-in-motion systems, among others. LPR-based technologies can be instrumental for capturing origin-destination (O-D) flows.  The need to understand O-D flows is important for developing transportation solutions and has planning, design, and operations implications.


The growing use of LPR has led to privacy concerns over how the data are used and who has access to it. Concerns range from worry about “Big Brother” and government tracking the movement of citizens to the storage, access and security. Some of this data could potently enable others to reconstruct individuals’ movements across space and time.  If travel patterns within the larger database are unique, other, external information can link license plate data back to specific individuals. This can conflict with an individual’s expectation of locational privacy.  Although U.S. courts have not associated a reasonable privacy expectation with a license plate, the collection and use of license plate data through LPR systems does raise concerns about privacy. While the information on a license plate itself may not be private, the use of collateral information raises privacy concerns.


Some states have passed legislation that governs how LPR technology can be used by law enforcement agencies. There has been relatively little activity related to regulating how transportation agencies can or should use the information that is produced by this technology.  While there are variations among state privacy laws, there are commonalities such as the requirement that state agencies collecting personal information must be authorized by law to collect such information, or that collection of such information must be necessary for the agency to perform its duties.


Transportation agencies continue to look for newer technologies and non-traditional sources of data that can support performance monitoring and transportation decision-making.  Until the privacy implications of various major use cases are understood, however, it will be difficult to determine both the potential benefits and the obstacles associated with the use of this technology.  The private sector and law enforcement  may be sources of best practices for keeping data anonymous,  developing  adequate sample sizes, determining how long data are retained, and how to productively engage with privacy advocates as well as other issues.  


Project Objectives


The objectives of this research were to (1) provide guidance for transportation agencies in developing policies governing their use of LPR data that adequately address privacy concerns and (2) identify the most significant potential transportation uses of LPR technology and their associated privacy risks. Topics addressed the following potential transportation uses of LPR technology:

  1. The types of motor vehicles affected.
  2. The demographics of individuals affected.
  3. How data are stored and for how long.
  4. How data are secured, and how access to the data is controlled and managed.
  5. Applicable laws and regulations governing the use of the data. 

The Final Report is available HERE.



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