§ 41.07 – What sampling options are available?

(a)    The available sampling options vary in:

(1)   the unit of sampling and measurement,

(2)   sampling structure,

(3)   efficiency options, and

(4)   sampling frequency.

(b)   The particular unit of sampling and measurement used in these ready-to-use sampling plans varies by mode and whether the service is scheduled (Table 41.01).

(1)   For non-scheduled services, the unit is in vehicle days.

(2)   For bus services (MB, CB, RB, and TB), separate sampling plans are available with units in one-way trips and in round trips.

(3)   For commuter rail, the unit is in one-way car trips.

(4)   For other rail modes, separate sampling plans are available in units of one-way car trips and one-way train trips.

Table 41.01.  Options for Unit of Sampling and Measurement

Service

Mode

Units of Sampling and Measurement

Non-Scheduled

Demand Response (DR, DT)

Vehicle days

Commuter Vanpool

Vehicle days

Scheduled

Bus (MB, CB, RB, TB)

One-way trips, round trips

Commuter Rail (CR)

One-way car trips

Other Rail Modes

One-way car trips, one-way train trips

(c)    Two options are provided for sampling structure—period-based and interval-based.  Interval-based sampling plans are available for bus services only.

(d)   Three efficiency options are provided:

(1)   Base Option – you must estimate both UPT and PMT through random sampling.

(2)   APTL Option – you must report a 100% count of UPT, estimate the average passenger trip length (APTL) through random sampling, and obtain annual PMT by multiplying the 100% UPT with the estimated APTL.

(3)   Grouping Option – you must divide your bus routes into two groups by route length.  The grouping option is available for period-based sampling plans only.

(e)    Three frequency options are provided for period-based sampling plans—quarterly, monthly, or weekly.  You may choose whichever of these options is best suited for your agency.  One factor to consider is that the annual realized sample size may be larger at a lower sampling frequency due to rounding.  Another factor is that a lower sampling frequency means a larger annual number of acts for random sampling.

(f)    Up to six frequency options are provided for interval-based sampling plans—every day, every 2nd day, every 3rd day, every 4th day, every 5th day, and every 6th day.  Three sets of these sampling plans are available for 7-day weekly service, 6-day weekly service, and 5-day weekly service, respectively.  The sampling plans for 7-day weekly service and the base option are similar to those in Circular 2710.1A.