§ 52.01 – What types of options does this template provide in its sampling plans?

(a)    Unit of sampling and measurement – the unit of service at which you do sampling, data collection, and estimation.

(b)   Sampling structure – period-based sampling or interval-based sampling.

(c)    Sampling frequency – how frequently you do sampling.

§ 52.03 – Must I pick a specific unit of sampling and measurement to use this template?

(a)    You must pick a specific unit of sampling and measurement before you start using this template.  The type of sample data you have available will often dictate your choice of a unit for sampling and measurement.

(1)   For non-scheduled services, such as demand response (DR and DT) or vanpool (VP), the unit of sampling and measurement is typically the vehicle day.  

(2)   For bus services, including bus (MB), commuter bus (CB), bus rapid transit (RB), and trolley bus (TB), you must decide if the unit will be a one-way bus trip or a round-trip bus trip.  It is a common practice to use a one-way bus trip as the unit of sampling and measurement.

(3)   For rail services, you must decide if the unit will be a one-way car trip, a round-trip car trip, a one-way train trip, or a round-trip train trip.  It is a common practice to use one-way passenger car trip as the unit of sampling and measurement.

(b)   The sample data you enter into this template will all be in this unit.

(c)    The resulting sampling plans from this template will also be in this unit.

(d)   The expansion factors you are going to use to expand your sample will also be in this unit if you are going to estimate both UPT and PMT with your sample data.

§ 52.04 – What options does this template provide on sampling structure?

(a)    Period-based sampling plans – you sample the same number of service units for each period (e.g., monthly).

(b)   Interval-based sampling plans – you sample the same number of service units one each sample day, and the interval between the sample days is constant.

(c)    In determining whether using interval-based sampling plans, you should consider their advantages and disadvantages:

(1)   the advantage of using a sampling plan that you have been using for years,

(2)   the advantage of using regular sample days throughout a year,

(3)   the disadvantage of a large number of times you need to sample during a year,

(4)   the disadvantage of not being able to consider the PPMT and grouping options, and

(5)   the disadvantage of a likely larger annual sample size due to rounding in determining the daily sample size.

§ 52.05 – What options does this template provide on sampling frequency?

(a)    This template provides you with three frequency options for period-based sampling – quarterly, monthly, and weekly.  For example, if weekly sampling requires 4 one-way bus trips per week, you must select at least 4 one-way bus trips at random from the full list of one-way bus trips that you expect to operate during a particular week.

(b)   This template provides you with up to 6 frequency options for interval-based sampling:

(1)   7-day weekly service – every day, every 2nd day, every 3rd day, every 4th day, every 5th day, and every 6th day.

(2)   6-day weekly service – every day, every 2nd day, every 3rd day, every 4th day, and every 5th day.

(3)   5-day weekly service – every day, every 2nd day, every 3rd day, and every 4th day.

(c)    You may choose whichever frequency option is best for your agency.

§ 52.07 – What should I consider in choosing a sampling frequency?

(a)    Period-based sampling plans:

(1)   Your cycle of minor schedule changes during a year.  For example, quarterly sampling may be appropriate if you routinely adjust your schedule every three months. 

(2)   The scale of your operation and the method you will be using to select a sample.  For example, it may become difficult to select a sample for an entire quarter if the number of service units involved in a quarter is too large for a spreadsheet to handle.

(3)   The realized annual sample size.  The realized annual sample size can be larger than the initial annual sample size due to rounding in allocating the initial annual sample to each frequency level.  This is particularly true for weekly sampling when the initial annual sample size is relatively small.  For example, if the initial annual sample size is 55 and you choose weekly sampling, the weekly sample size would be 2 and the realized annual sample size would be 104. 

(b)   Interval-based sampling plans:

(1)   Your staffing needs for data collection.

(2)   The number of times you need to do sampling.  The number of times is larger with plans of higher frequency (e.g., every vs. every 2nd day). 

(3)   The annual total sample size.  The degree of rounding is higher with plans of higher frequency.

§ 52.09 – What efficiency options does the template include?

(a)    The template includes a number of options for you to consider in improving your sampling efficiency:

(1)   The base option.

(2)   The APTL option.

(3)   The PPMT option.

(4)   The grouping option. 

(b)   You may use the base option if you are going to estimate both UPT and PMT (i.e., you will not be using 100% counts for either UPT or PMT), and

(c)    Any of the other three options has the potential to improve your sampling efficiency over the base option:

(1)   Sampling plans under the APTL option are based on how APTL in absolute terms varies across your service units.

(2)   Sampling plans under the PPMT option are based on how APTL relative to average route length varies across your service units.

(3)   Sampling plans under the grouping option are based on the idea that relevant statistical variation may be smaller across service units within sub-segments of your service than across all service units of your entire service.

(d)   Additional options become available when service grouping is combined with each of the other three efficiency options.

§ 52.11 – Which of these efficiency options are available to me?

(a)    All four efficiency options are available for period-based sampling.  Only the first two are available for interval-based sampling.

(b)   The base option is available to you if you have data on PMT from your sample.  But it is not recommended in most cases if a 100% count of annual UPT is available and reliable.

(c)    The APTL option is available to you if you meet the following two criteria:

(1)   you are going to report a 100% count of annual UPT, and

(2)   you have data on both UPT and PMT from your sample data.

(d)   The PPMT option is available to you if you meet all of the following criteria:

(1)   you are going to report a 100% count of annual UPT,

(2)   you have data on both UPT and PMT from your sample data,

(3)   your service is a fixed-route service,

(4)   you have your 100% count of annual UPT for each route, and

(5)   you have data on annual total vehicle revenue miles and annual total vehicle revenue one-way trips for each route.

(e)    The grouping option is available to you as long as you have some basis for dividing your service into two or more groups. 

§ 52.13 – How do I divide my scheduled service if I want to consider the grouping option?

(a)    Grouping is usually by route when there is a small number of routes or by groups of routes that are similar.

(b)   You are going to determine the similarity of service units on your expectations from your prior knowledge of your service.  

(c)    The most efficient grouping depends on other efficiency options you consider: 

(1)   If your sampling plan follows the base option, define groups so that within each group, they are similar with respect to PMT per service unit.  For example, you may group heavily used long routes separately from lightly used shorter routes.

(2)   If your sampling plan follows the APTL option, define your groups so that within each group they have similar APTL.  For example, if your express route customers travel particularly long distances, you may separate your express and local services as two groups.  As another example, if some of your local routes are particularly longer than the other local routes, you may further divide your local service into two groups.

(3)   If your sampling plan follows the PPMT option, define your groups so that the routes within each group are similar with respect to the fraction of a route’s length that passengers typically ride.  For example, if on some routes passengers tend to ride most of length of the route (as is the case for some express routes) while on other routes passengers tend to ride for only a small part of the route’s full length, separate those routes into different groups.  Consider another example.  If a system has a mix of radial routes (routes with one end in the downtown), diagonal routes (routes that pass through the downtown), and crosstown routes (routes that don’t pass through the downtown), the average fraction of route length that passengers ride tends to be smaller on the diagonal and crosstown routes and longer on the radial routes.  In this case, radial routes could be grouped separately from diagonal and crosstown routes.

§ 52.17 – What should I consider in general when I consider grouping my service?

(a)    Strike a balance between the number of groups and the potential reduction in necessary sample size.  In most cases, you will only want to deal with two or three groups.

(b)   You may try different ways of grouping your service and choose one particular grouping based on its efficiency improvement and your administrative convenience. 

(c)    The grouping option may be used for administrative convenience alone: 

(1)   You may treat your different contractors of service for a given mode as separate groups when each is responsible for sampling and collecting data.

(2)   You may treat your operational divisions as separate groups if each is responsible for sampling and collecting data.

(3)   You may treat your commuter vanpool separately from your other vanpool services.