4.1 This practice will permit various agencies to compare intersection turning movement data using two foundational principles: truth in data and base data integrity. These two principles help ensure that intersection turning movement counts can be correctly interpreted and appropriately used to improve the safe and efficient operation of intersections. The principles may be summarized as follows:

4.1.1 Truth in Data Principle—The truth in data principle provides information that assists potential data users to understand what the data do and do not mean. The opportunity to collect data that advise safe and efficient transportation carries with it the obligation to report how the data were collected, edited, summarized, and reported.

4.1.2 Base Data Integrity Principle—The principle of base data integrity retains the field data collected. In keeping with the principle of base data integrity, it is possible to look at the original data to verify any subsequent changes to the data. In intersection turning movement and other data collection activities, field data may be edited, adjusted, and then summarized and reported. Whatever steps are taken to ensure the quality of the data summarized, the base data must not be corrupted. In keeping with the principle of truth in data, editing and adjustments are documented.

1.1 This practice for intersection turning movement data acquisition was developed to improve its quality by specifying the data items to be collected and a procedure for documenting the results. Such a practice will provide the ability to compare these data over time within governmental agencies and among different governmental agencies. While there are national and international standards for road segment traffic data, there is not a practice for intersection turning movement data acquisition.

1.2 Units—The values stated in inch-pound units are to be regarded as the standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.

1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.