23 C.F.R. § 1340.3 Basic design requirements.
Title 23 - Highways
Surveys conducted in accordance with this part shall incorporate the following minimum design requirements: (a) Probability-based requirement. The sample identified for the survey shall have a probability-based design such that estimates are representative of safety belt use for the population of interest in the state and sampling errors may be calculated for each estimate produced. (b) Observational requirement. Minimum requirements include the following: (1) The sample data shall be collected through direct observation of seat belt use on roadways within the State, conducted completely within the calendar year for which the seat belt use rate is being reported; (2) Seat belt use shall be determined by observation of the use or non-use of a shoulder belt; (3) Observers shall be required to follow a predetermined, clear policy in the event that observations cannot be made at an assigned site at the specified time (due to heavy rain, construction, safety problems, etc.); (4) Instructions to observers shall specify which road and which direction of traffic on that road are to be observed (observers must not be free to choose between roads at an intersection); and (5) Observers shall follow clear instructions on how to start and end an observation period and how to stop and start observations if traffic flow is too heavy to observe all vehicles or if vehicles begin moving too quickly for observation (to remove any possible bias, such as starting with the next belted driver). (c) Precision requirement. The relative error (standard error divided by the estimate) for safety belt use must not exceed 5 percent.
Title 23: Highways
PART 1340—UNIFORM CRITERIA FOR STATE OBSERVATIONAL SURVEYS OF SEAT BELT USE
§ 1340.3 Basic design requirements.
