§ 30.01 – When should I consider using alternative sampling plans?

(a)    An alternative sampling plan is equivalent to an alternative sampling technique as defined in the NTD Reporting Manual.

(b)   If the sampling options provided in the companion template of this NTD Sampling Manual meet your needs, it is to your advantage to use template sampling plans.

(c)    You should consider using alternative sampling plans when the companion template does not cover the best option for your specific situation.  The companion template provides many options for you to explore and consider for the vast majority of possible situations, but it may not cover the best option for all situations. 

§ 30.03 – What additional requirements should alternative sampling plans meet?

(a)   Alternative sampling plans must meet FTA’s 95% confidence and 10% precision levels.

(b)   In addition to these basic statistical requirements, alternative sampling plans should also meet the following requirements:

(1)   They are based on the conditions of your service.  That means that they should be developed with sample data collected from a random sample of your service.

(2)   The sample data used for developing alternative sampling plans have a minimum sample size of 50 service units.

(3)   They contain a margin of safety of at least 25%.  That is, the final sample size of an alternative sampling plan is at least 25% greater than what you would get from using the sample data directly.

(4)   The final sample size of any alternative sampling plan is at least 50.

(c)    Template sampling plans also should meet the additional requirements in (b) as specified in Section 50.

§ 41.01 – Under what conditions may I use ready-to-use sampling plans?

(a)    Small Systems – If you operate no more than 30 vehicles operated in maximum service for all modes combined and if you choose to sample for determining your annual service-consumed data for any of the modes you operate. 

(b)   New Mode – If you will be sampling and reporting for the first time this current report year for a particular mode that you do not already operate.  For example, you would meet this condition if you will add light rail (LR) service this year, but you have not operated this service previously, or

(c)    New Type of Service – If you will be sampling and reporting this current report year for a particular type of service for the first time.  For example, you would meet this condition if you previously directly operated all of your bus (MB) service, but will contract out part or all of that service to a private entity for this year, or

(d)   Major Changes of Service – You have made major changes to your service since your last sampling year, or

(e)    No Sample Data – If you have reported your service to the NTD before through random sampling, but no longer have the original sample data, or

(f)    Sample Data Not Reliable – If you have reported your service to the NTD before through random sampling, but the sample data are found to be not reliable, or

(g)   Sample Data Not Enough – if you have reported your service to the NTD before through random sampling, but the sample size is smaller than 50 service units.

§ 41.03 – If I am using a ready-to-use sampling plan this year, may I use it again for my next report year?

(a)    You should not use it again if your next report year is your mandatory sampling year.  After you have collected the sample data from this year, you should develop a template sampling plan with that sample data for your next report year.

(b)   You may use it again for the next report year if that year is not your mandatory sampling year.

(c)    You may use it while you operate no more than 30 vehicles operated in maximum service for all modes combined.

§ 41.05 – For what modes are ready-to-use sampling plans available?

(a)    For non-scheduled services, they are available for demand response services (DR and DT) and commuter vanpool.  You should not use the ready-to-use sampling plans for commuter vanpool if your vanpool service does not serve commuters exclusively.

(b)   For scheduled services, they are available for bus services (bus (MB), commuter bus (CB), bus rapid transit (RB), and trolleybus (TB)), commuter rail (CR), and other rail modes. 

§ 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.

§ 43.01 – What period-based sampling plans are available for non-scheduled services?

 (a)    Table 43.01 shows the sampling plans available for demand response services (DR and DT) and commuter vanpool, respectively.

(b)   Sample size is stated in the number of vehicle days.

(c)    Separate sampling plans are available for the base option and the APTL option.

(d)   Sample size is shown for the entire year and for the relevant period for each frequency.

Table 43.01.  Period-Based Ready-to-Use Sampling Plans for Non-Scheduled Services

Sampling Frequency Sample Size

Demand Response

Commuter Vanpool

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

Quarterly Vehicle Days for a Quarter

13

22

31

45

Total Sample Size for Year

52

88

124

180

Monthly Vehicle Days for a Month

5

8

10

15

Total Sample Size for Year

60

96

120

180

Weekly Vehicle Days for a Week

1

2

2

4

Total Sample Size for Year

52

104

104

208

§ 43.03 – What period-based ready-to-use sampling plans are available for bus services?

(a)    Table 43.03 shows the available ready-to-use sampling plans for bus services, including bus (MB), commuter bus (CB), bus rapid transit (RB), and trolleybus (TB). 

Table 43.03.  Period-Based Ready-to-Use Sampling Plans for Bus Services

Sampling Frequency

Sample Size for Period and Year

One-Way Trips

Round Trips

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

With Route Grouping

Without Route Grouping

With Route Grouping

Without Route Grouping

(1)

(2)

(3)

(4)

(5)

(6)

Quarterly

Trips for a Quarter

52

78

138

39

59

103

Total Sample Size for Year

208

312

552

156

236

412

Monthly

Trips for a Month

18

27

46

13

20

35

Total Sample Size for Year

216

324

552

156

240

420

Weekly

Trips for a Week

4

6

11

3

5

8

Total Sample Size for Year

208

312

572

156

260

416

(b)    Sampling plans are provided separately for one-way trips and round trips. 

(c)   The number of one-way trips in a sampling plan based on round trips is about 50% greater than the number of one-way trips in a sampling plan based on one-way trips.  A sampling plan based on round trips requires a larger number of one-way trips because the pair of one-way trips making up a round trip are not selected randomly or independently.

(d)    If you choose the base option:

(1)   use column (3) to find the sample size in one-way trips, and

(2)   use column (6) to find the sample size in round trips.

(e)   If you choose the APTL option, you may choose one of two options:

(1)   With Route Grouping – Use column (1) to find the sample size in one-way trips and column (4) to find the sample size in round trips.  In using this option, you must divide your routes into two groups on the basis of route length and do sampling and estimation separately for each group.  For example, if you operate 10 routes, put the 5 routes with the shortest route distances in the group of short routes and the other 5 routes in the group of long routes. 

(2)   Without Route Grouping – If you prefer not to deal with grouping your routes, use column (2) to find the sample size in one-way trips and use column (5) to find the sample size in round trips.

§ 43.07 – What period-based sampling plans are available for commuter rail?

(a)    Table 43.05 shows the available ready-to-use sampling plans for commuter rail (CR). 

(b)   Sample size is in one-way car trips.

(c)    Separate sampling plans are available for the base option and the APTL option.

Table 43.05.  Period-Based Ready-to-Use Sampling Plans for Commuter Rail (CR)

Sampling Frequency

Sample Size for Period and Year

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

Quarterly

One-Way Car Trips for a Quarter

13

80

Total Sample Size for Year

52

320

Monthly

One-Way Car Trips for a Month

5

27

Total Sample Size for Year

60

324

Weekly

One-Way Car Trips for a Week

1

7

Total Sample Size for Year

52

364

§ 43.09 What period-based sampling plans are available for other rail modes?

(a)    Table 43.07 shows the available ready-to-use sampling plans for other rail modes, including light rail (LR), heavy rail (HR), monorail and automated guideway (MG). 

(b)   Separate sampling plans are available for one-way train trips and one-way car trips.

(c)    Separate sampling plans are available for the base option and for the APTL option.

Table 43.07.  Period-Based Ready-to-Use Sampling Plans for Other Rail Modes

Sampling Frequency

Sample Size for Period and Year

One-Way Train Trips

One-Way Car Trips

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

Reporting 100% UPT

(APTL Option)

Not Reporting 100% UPT

(Base Option)

Quarterly

Trips for a Quarter

13

45

13

72

Total Sample Size for Year

52

180

52

288

Monthly

Trips for a Month

5

15

5

24

Total Sample Size for Year

60

180

60

288

Weekly

Trips for a Week

1

4

1

6

Total Sample Size for Year

52

208

52

288

§ 43.11 – What interval-based ready-to-use sampling plans are available for bus services?

(a)    Table 43.09 shows the available ready-to-use sampling plans for bus services, including bus (MB), commuter bus (CB), bus rapid transit (RB), and trolleybus (TB). 

(b)   Separate sampling plans are available for the base option and the APTL option.

(c)    In determining whether using interval-based sampling plans, you should consider the tradeoff between at least two factors:

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

(2)   the potentially lost opportunity of a lower sample size.

(d)   You should first determine the number of weekly operating days for your next sampling year, and choose the set of sampling plans accordingly.  For example, if you will be operating 7 days a week, you should not consider any of the sets for the other weekly operating patterns.

(e)    You may choose any of the above plan numbers that correspond to the weekly operating pattern of your service.

Table 43.09.  Interval-Based Ready-to-Use Sampling Plans for Bus Services

Plan Number

Frequency of Sampling

Operating 7 Days a Week

Operating 6 Days a Week

Operating 5 Days a Week

Daily One-Way Bus Trips

Total Sample Size for Year

Daily One-Way Bus Trips

Total Sample Size for Year

Daily One-Way Bus Trips

Total Sample Size for Year

Base Option

1

Every Day

2

730

2

624

2

520

2

Every 2nd Day

3

549

3

468

4

520

3

Every 3rd Day

5

610

6

624

7

609

4

Every 4th Day

7

644

9

702

12

780

5

Every 5th Day

10

730

13

819

N/A

N/A

6

Every 6th Day

15

915

N/A

N/A

N/A

N/A

APTL Option

1

Every Day

1

365

1

312

1

260

2

Every 2nd Day

2

366

2

312

3

390

3

Every 3rd Day

3

366

4

416

5

435

4

Every 4th Day

4

368

6

468

8

520

5

Every 5th Day

6

438

8

504

 

 

6

Every 6th Day

10

610

 

 

 

 

§ 51.01 – Under what conditions should I develop a template sampling plan for next year?

(a)    If you have previously been using a ready-to-use sampling plan and the next report year is your mandatory sampling year;

(b)   If you have previously been using a sampling plan, but it is not based on the conditions of your service;

(c)    If you have previously been using a template sampling plan, but you must revise it for your next sampling year according to Subsection 56; or

(d)   If you previously have been using an alternative sampling plan, but would like to:

(1)   improve your sampling efficiency,

(2)   change the unit of sampling and measurement,

(3)   change the sampling structure, or

(4)   use a different sampling frequency.

§ 51.02 – Should I consider template sampling plans if I am a small system and want to sample?

(a)    You do not have to consider template sampling plans.  You may continue using ready-to-use sampling plans while you continue operate no more than 30 vehicles operated in maximum service for all modes combined.

(b)   It is likely to be in your interest to consider template sampling plans. 

(c)    If the sample size requirement is considerably smaller for template sampling plans than for ready-to-use sampling plans, the benefit is likely to be much greater than your cost from considering template sampling plans. 

§ 51.03 – Does this Manual have a companion tool that I may use?

(a)    Yes, this companion tool is an Excel template, “The NTD Sampling Template.xlsm.”

(b)   It is specifically designed for you to develop template sampling plans.

(c)    You may download a copy of this template from the NTD homepage at www.ntdprogram.gov. 

§ 51.05 – What is the scope of this template?

(a)    You may use it for any mode of transit service, such as bus (MB), that is explicitly recognized by the NTD.

(b)   You may use it for any type of service, such as directly operated (DO), that is explicitly recognized by the NTD.

(c)    You may use it with sample data in any unit of sampling and measurement.

§ 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.

§ 53.01 – What data must I have to use this template?

(a)    You must have a set of sample data collected recently from your service for the mode and type of service for which you would like to have a new template sampling plan. 

(1)   The sample data must be at the unit of sampling and measurement you have chosen for your sampling plan.  For example, if your sampling plan is in one-way bus trips, the sample data should show the UPT and PMT and other identification information for each one-way bus trip in your sample.

(2)   Follow the instructions in the template for details on data items and format required and how they should be entered into the template.

(b)   You should use your NTD sample if it is available and you have not made major changes to your service since the data were collected.

(c)    Otherwise, you may use data that have been collected for non-NTD purposes: 

(1)   One good source of non-NTD sample data for scheduled services is a comprehensive operational analysis (COA).  Typically, all trips or a large portion of all trips on your schedule are checked by ride-checkers or by APCs during a concentrated period.

(2)   Make sure that the non-NTD source of sample data has the required information for using this template.  For example, between-stop distances often are not collected during COA ride checks, and the resulting ride check data would not be useful if you do not have predetermined between-stop distances for your entire service.

(d)   The sample size of the sample data from any source must be 50 or more service units.

(e)    If you do not have a set of sample data recently collected from your service for the mode and type of service, then you should use one of the other types of sampling plans, such as ready-to-use sampling plans.

§ 53.03 – Must I identify and correct errors with my sample data before I enter them into the template?

(a)    Yes, you must identify and correct errors in your sample data for using the template.

(b)   If you are using sample data from previous report years, you should have identified and corrected such errors in developing your estimates then; make sure that you use the final version of your sample data. 

(c)    Refer to Subsection 67 for identifying and correcting errors in your sampling data during the course of an entire report year as you collect sample data.

(d)   If you are using sample data from the current report year, identifying and correcting errors in the sample data now for developing sampling plans saves you from doing it when you develop your estimates later for reporting purposes.

(e)    At a minimum, you should conduct the following checks to identifying potential errors:

(1)   Overall consistency – UPT and PMT should be closely related across all sample units.  For period-based sampling plans, check for errors if cell D26 in the PeriodCalculations worksheet is smaller than 0.5.  For interval-based sampling plans, check for errors if cell D20 in the IntervalCalculations worksheet is smaller than 0.5.

(2)   Consistency at the level of sampling units – UPT and PMT should both be zero or both be positive.  Check for errors if one is zero but the other is positive.

(3)   Comparing APTL with route length – Calculate the ratio of PMT over UPT and compare the result to the maximum length of your route.  This check is not applicable to demand response services.

(4)   If you consider the PPMT option, calculate the ratio of PMT over PPMT for each sample unit; the ratio should not be greater than 1.

(f)    It is in your interest to keep your sample data free of errors.  Experience indicates that sample data with errors tend to result in larger sample sizes than sample data free of errors. 

§ 53.05 – Do interval-based sampling plans have any special requirement for the sample data used in developing them?

(a)    Yes, the sample data must have 2 or more service units for every sample day.

(b)   If you sampled 3 one-way bus trips every 2nd day with an annual total sample of 549 trips during your last sampling year, your sample data would meet this requirement.  If you have identified and corrected errors in your sample data, you may use them for developing interval-based sampling plans with the template. 

§ 53.07 – What other data do I need to use this template?

(a)    If you want to consider the grouping option, you must have data:

(1)   on the size of each service group in the number of service units operated during the period for which the sample data were collected, and

(2)   on the expected size of each service group for future sampling years. 

(3)   Follow the instructions in the template on how you should enter the information on group size.

(b)   If you want to consider combining the grouping option with the APTL option, you must enter into the template whether you will have reliable 100% counts of UPT for each service group for estimating your annual PMT.  Follow the instructions in the template on where you should enter this information.  Your input affects several things:

(1)   The efficiency of your sampling plan.  In general your sampling plan is more efficient if you will have reliable 100% counts of UPT by service group.

(2)   How you should estimate your annual PMT.  For example, you will need to estimate your annual PMT separately for each service group if you have 100% counts of UPT by service group.  Refer to Subsection 83 for more guidance on estimation.  

(3)   The information you need to get from the template for determining whether you need to revise your template sampling plan.  Refer to Subsection 56 for more guidance on revision of sampling plans.

(c)    If you want to consider interval-based sampling plans, you must have information on the annual number of days of service and the daily number of trips.

§ 53.09 – What sample data should I use to develop template sampling plans for next year?

(a)    If you are not sampling this year, you should use the sample data from your most recent previous sampling year.

(b)   If you are sampling this year, you should use the sample data from this year.  It is critical that you process your sample data as they become available.  The objective is that you can apply the companion template of this Manual to the cumulative sample data any time during this year.  Refer to Section 60 for processing your sample data.

(1)   If you are familiar with the companion template of this Manual, you should wait until a couple of weeks before the end of this year to use the template.  It is fine if you miss a few service units in your annual NTD sample for this purpose.  Note that you will still need to use the full sample to estimate your annual service-consumed data for NTD reporting.

(2)   If you are not familiar with the companion template, you should start learning to use the companion template with your sample data from this year.  Once you become familiar with the template, you should still wait until a couple of weeks before the end of this year to use the template.

§ 53.11 – How does this template deal with fluctuations in sample data from one year to another for a given service?

(a)    The measured statistical variation in APTL or any relevant characteristic of your service fluctuates from one year to another. 

(b)   Such fluctuations can occur from minor changes in your service or changes in how people use your service even if you do not adjust your service.

(c)    Fluctuations can also occur due to errors in data collection as a result of sampling.

(d)   This template has built in a 25% margin of safety against such fluctuations.

(e)    This margin of safety is equivalent to increasing the minimum precision level from 10% to 8.94% at the same 95% confidence level.

§ 53.13 – Why do such annual fluctuations in sample data require a margin of safety?

(a)    FTA’s 95% confidence and 10% precision levels are imposed on your estimates of annual service-consumed data.

(b)   The template, on the other hand, can only impose these requirements on your template sampling plans, but not on the estimates you develop with data collected according to your template sampling plans.

(c)    Whether the estimates of annual service-consumed data from the sample data collected according to the template sampling plans meet FTA’s requirements depends on how the sample data fluctuate over time:

(1)   If the statistical variation is greater in the sample data used to develop your template sampling plan, your estimates will meet FTA’s requirements.

(2)   If the statistical variation is smaller in the sample data used to develop your template sampling plan, your estimates may not meet FTA’s requirements.  The margin of safety is built in to prevent such violations from happening.

§ 53.15 – How does this template ensure adequate sample size for developing template sampling plans in the future?

(a)    Statistical theory shows that a minimum sample size of 50 is required to get an adequately precise estimate of how much APTL or any other relevant characteristic of your service varies across your service. 

(b)   This template has built in a minimum sample size of 50 for all new template sampling plans.

§ 54.01 – How do I use this template?

(a)    You must choose Enable Macros upon opening the template.

(b)   You must check a checkbox in the Cover Worksheet to develop interval-based sampling plans.  The default is for period-based sampling plans.

(c)    You must follow the instructions provided in the template.

(d)   This template is illustrated with actual sample data in “The NTD Sampling Template with Sample Data.xlsm.” 

(e)    This illustrated template is available for download at the NTD webpage: www.ntdprogram.gov. 

§ 54.03 – What does the template output include?

(a)    The output includes a set of several sampling plans as a result of the input data you have entered.

(b)   The sampling plans in this set differ in their efficiency options and sampling frequency.

(c)    For period-based sampling plans, the number of sampling plans in this set varies with the efficiency options that your input data allow.  It ranges from 6 sampling plans if you do not consider the PPMT and grouping options to 18 sampling plans if you consider them.

(d)   For interval-based sampling plans, the number of sampling plans in this set varies with your weekly service patterns.  It ranges from 8 sampling plans if you operate your service 5 days a week to 12 sampling plans if you operate 7 days a week.

(e)    The set of sampling plans changes when you change your input data. 

§ 55.01 – What should I consider in selecting one from the set of template sampling plans?

(a)    When your data allow, you should take the full advantage of the template by considering all possibilities, particularly both period-based and interval-based sampling plans and alternative ways of grouping your service.  This exploratory use of the template is especially useful when you have not used template sampling plans before.   

(b)   Once you have done the exploratory work, you should consider all five elements of a sampling plan: 

(1)   unit of sampling and measurement,

(2)   sampling structure,

(3)   efficiency options,

(4)   sampling frequency, and

(5)   annual sample size.

(c)    You should consider tradeoffs among the following characteristics of sampling plans:

(1)   sampling cost – it is closely related to the annual sample size and to the unit of sampling and measurement.

(2)   complexity of sampling plans – the grouping and PPMT options, for example, make sampling and estimation more complex. 

(3)   administrative convenience – how a sampling plan matches your institutional arrangements for sampling and data collection purposes.

(d)   If you want to choose an interval-based sampling plan for the current report year and want to consider interval-based sampling for future years:

(1)   you should consider those plans that require sampling 2 or more service units per sample day.  You must have sample data for 2 or more service units for each sample day in order to use the template for developing new interval-based sampling plans in the future.  Or

(2)   you may increase the daily sample size for a desired sampling frequency (e.g., every 3rd day) if the template results in a daily sample size of 1 for that frequency.       

§ 55.03 – Should I keep a copy of the used template that contains my sample data and my chosen template sampling plan?

(a)    Yes, you should keep a copy of the used template that contains your sample data and the final sampling plans, including the sampling plan you have chosen.  It is useful later for several purposes.

(b)   You may need it for NTD requirements on record keeping.

(c)    You may also need it for the following purposes:

(1)   Get information about the sample data for determining whether you need to revise your template sampling plan.  Refer to Subsection 56 for guidance on that.

(2)   Remind you what you have entered into the template on whether you will have reliable 100% count of UPT by service group if your template sampling plan is based on the APTL option with service grouping.  Refer to Subsection 83 for guidance on estimation under the APTL option.

§ 55.05 – How does my choice of efficiency options affect my choice of estimation methods?

(a)    Your choice of an efficiency option determines your method of estimation.

(b)   Follow the guidance on estimation in:

(1)   Section 70 if you choose the base option.

(2)   Subsection 83 if you choose the APTL option.

(3)   Subsection 85 if you choose the PPMT option. 

§ 55.07 – May I change template sampling plans from one report year to another?

(a)    Suppose that:

(1)   you have developed a set of final template sampling plans with sample data from a previous sampling year, and

(2)   you are using one of these template sampling plans this year.

(b)   The answer depends on whether you are required to revise your current sampling plan for next year.  Refer to Subsection 56 on how you may determine the need for revision.

(c)    You may change to a different sampling plan from the current set of final template sampling plans if you are not required to revise your current sampling plan.

(d)   You may change to a different sampling plan from an entirely new set of template sampling plans if you choose to develop new sampling plans using your sample data from the current report year.

(e)    You must not change to a different sampling plan from the current set of template sampling plans if you are required to revise your current sampling plan.

§ 55.09 – May I change sampling plans during a report year?

(a)    You should not change sampling plans during the same report year if you have not made major changes to your service. 

(b)   You should increase the necessary sample size by 50% with the same template sampling plan you used during the first part of the year if you have made major changes to your service.  For example, if you were sampling 4 one-way bus trips each week before the major changes, you should change to sample 8 one-way bus trips each week after those changes.

(c)    Table 55.01 shows this guidance in a tabular format.

Table 55.01.  Tabular Guidance on Changing Sampling Plans in a Report year

If you

then you should

by

have not made major changes to your service

not change your sampling plan during a report year

 

you have made major changes to your service

adjust your sampling plan during a report year

increasing the necessary sample size by 50%

§ 55.11 – How should I implement a template sampling plan?

(a)    You must not implement a template sampling plan at a unit that is smaller than the unit used in developing the original sampling plan.  For example, if your plan is to sample 3 round trips per week, you must not implement it by sampling 3 one-way trips per week.

(b)   You may choose to sample and measure at a unit that is greater than the unit used in developing the original template sampling plan.  For example, if your plan is to sample 4 one-way trips per week, you may implement it by sampling 4 round trips per week instead. 

(c)    You may only want to do (b) during the first year of implementing a template sampling plan.  For example, once you have the sample data in round trips from the first year, you should use the sample data from the first year to develop a new template sampling plan in round trips for future years.

§ 56.03 – Why do I need to consider revision?

(a)    Your service and the traveling habits of your customers change naturally over time.  

(b)   To meet certification requirements:

(1)   Such service and habit changes may increase the statistical variation in key quantities (e.g., PMT, APTL) and hence require larger sample sizes.

(2)   The sampling plans produced by this template are only certified to meet FTA’s requirements of 95% confidence with 10% precision for certain sampling cycles, presuming no major changes in your service.  

(3)   After this time, or after major changes in your service, a new template sampling plan must be developed to maintain certification of compliance with the FTA requirements.

(c)    To get more efficient sampling plans:

(1)   Such service and habit changes sometimes may reduce the statistical variation of key quantities (e.g., PMT, APTL).

(2)   You would be able to take advantage of such reduced variation by revising your template sampling plans using your most recent sample data that reflect these service and habit changes.

§ 56.05 – Under what conditions should I revise my template sampling plan?

(a)    If your next sampling year is your mandatory revising year, you must revise your template sampling plans.  Or

(b)   If you have made major changes to your service since you started using the current template sampling plan, you must consider revising your template sampling plan.

§ 56.07 – How do I know if next year is a mandatory revising year for me?

(a)    If you are required to sample every year, every 6th year is your mandatory revising year.  For example, if you used your 2010 NTD sample to develop a template sampling plan, report year 2016 is your mandatory revising year.

(b)   If you are required to sample every 3rd year, every 9th year is your mandatory revising year.  For example, if you used your 2010 NTD sample to develop a template sampling plan, report year 2019 is your mandatory revising year. 

(c)    Follow the Reporting Manual to determine whether you are required to sample every year.

§ 56.09 – What are considered major changes to my service?

(a)    A major change is any change you make to your service that is likely to lead to major changes in the statistical variation in a relevant quantity of your service. 

(b)   The relevant quantity of your service varies with the sampling options you choose.  It is PMT if you choose the base option, APTL if you choose the APTL option, etc.

(c)    The following are examples of a major change:

(1)   Making transfers fare-free for all passengers.

(2)   Adding or cutting express routes to the base of all local service.

(3)   Expanding or contracting your service by at least 25% in vehicle revenue miles.

(4)   Service restructuring that affects at least 25% of your service in vehicle revenue miles.

§ 56.11 – How do I determine if I must revise my template sampling plan after I have made major changes to my service?

(a)    Enter your sample from the current report year into the companion template as if you were going to develop a new template sampling plan. 

(1)   Enter your PPMT data if your current template sampling plan follows the PPMT option.

(2)   Enter the corresponding grouping data if your current template sampling plan follows the grouping option.

(b)   For period-based sampling, go to the PeriodPrecision Worksheet.  The index number you need depends on the efficiency option you have chosen for the current template sampling plan.  For example, you must use the value in cell D6 of Part A, Figure 56.01 (=32.7) if your template sampling plan is based on the APTL option with service grouping and if you have chosen to use your 100% UPT count by group in developing your annual estimates.

(c)    For interval-based sampling, go to the IntervalPrecision Worksheet.  The index number you need also depends on the efficiency option you have chosen for your current template sampling plan.  For example, you must use the value in cell C5 of Part B, Figure 56.01 (=31.3) if your template sampling plan is based on the APTL option.

(d)   You must revise your sampling plan if the precision index is smaller than 10.0.

A. PeriodPrecision Worksheet

B. IntervalPrecision Worksheet

Figure 56.01.  Layout of the PeriodPrecision and IntervalPrecision Worksheets

§ 57.01 – How do I certify my template sampling plan?

(a)    You must certify that that your template sampling plan meets FTA’s 95% confidence and 10% precision levels through your annual reporting process.

(b)   You should follow the current Reporting Manual on how exactly you may do that.

(c)    This certification of your template sampling plan through the annual reporting process is conditional:

(1)   Your template sampling plan must use the 25% margin of safety according to Subsection 53.

(2)   You revise your template sampling plans over time according to Subsection 56.

§ 91.01 What do the sampling-related terms mean?

Alternative sampling plan.  A sampling plan that reflects the conditions of your service, and is independently developed and certified by a qualified statistician to meet FTA’s 95% confidence and 10% precision levels.  It is one of two forms of customized sampling plans.  The other form is template sampling plans.  It is equivalent to an alternative sampling technique as defined in the NTD Reporting Manual.

Confidence level.  The chance of an estimate of service-consumed data obtained through random sampling falling within a particular range of the true value. FTA requires a minimum level of 95% confidence for estimates of annual UPT and annual PMT reported to the NTD.  A particular confidence level is only meaningful when it is stated with a particular precision level.

Customized sampling plan.  A sampling plan that reflects the conditions of your service and meets FTA’s 95% confidence and 10% precision levels.  It is either a template sampling plan or an alternative sampling plan.  It differs from a ready-to-use sampling plan in that it takes account of the specific characteristics of your service.

Efficiency option.  A characteristic of a sampling plan that affects its sampling efficiency.

Initial annual sample size.  The annual necessary sample size of a period-based template sampling plan that is determined from the companion spreadsheet template before it is allocated to each quarter, month, or week.  This can differ from the realized annual sample size for a given set of sample data.

Mandatory revising year.  A report year for which you must consider whether you need to revise your template sampling plan. 

Margin of safety.  A percent increase in the statistical variation of your sample data in developing a template sampling plan.  For example, if the statistical variation of your sample is S and the margin of safety is 25%, you must use 1.25S as the statistical variation in developing your template sampling plan.  A margin of safety of 25% is used automatically for all period-based template sampling plans.  If you develop alternative sampling plans, you should also use this margin of safety.  The objective is to counter the potential fluctuations in the statistical variation in a sample from one year to another due to sampling and other reasons. 

Major change to a service.  Any change to your service that is likely to lead to major changes in how your customers use your service.  Examples of major changes include making transfers fare free; adding or cutting express routes; expanding or contracting your service by more than 25% in vehicle revenue miles; or restructuring your service affecting more than 25% of your service in vehicle revenue miles.

Necessary sample size.  The sample size that meets FTA’s minimum 95% confidence and 10% precision levels and uses a 25% margin of safety.

Precision index.  A number that reflects the level of precision that your current NTD sample achieves in the resulting annual total PMT.  It is used for you to determine whether you must revise your current template sampling plan after you have made major changes to your service since you started using the current template sampling plan.  Once you have entered your current sample data into the template for this Sampling Manual as if you are going to develop new template sampling plans, this precision index is made available in the PeriodPrecision Worksheet for period- based sampling and in the IntervalPrecision Worksheet for interval-based sampling. 

Precision level.  The degree of errors in an estimate of service-consumed data obtained through random sampling that is stated in percentage terms relative to the true value.  FTA requires a minimum of 10% precision for estimates of annual service-consumed data reported to the NTD.  A particular precision level is only meaningful if it is stated with a particular confidence level.

Random sampling.  Selection of one or more service units at random from a list of service units to be operated.

Ready-to-use sampling plan.  A sampling plan that has been developed specifically for this Sampling Manual with sample data from a variety of transit agencies.  It does not necessarily reflect the conditions of your service.  Ready-to-use sampling plans have limited applicability.

Realized annual sample size.  The annual necessary sample size of a period-based template sampling plan that is based on quarterly, monthly, or weekly sampling.  For example, if you choose weekly sampling and your template sampling plan requires 3 one-way trips per week, the realized annual sample size would be 156 one-way trips.

Sample size.  The number of service units that are sampled, and for which unlinked passenger trips and passenger miles traveled are measured.

Sampling efficiency.  The degree to which a sampling plan minimizes the necessary sample size for meeting FTA’s confidence and precision levels.  Sampling plans that take advantage of certain characteristics of your service can sometimes require a smaller necessary sample size.  A smaller necessary sample size reduces the time and cost of sampling, data collection, and data processing.

Sampling frequency.  The number of times per year that a sample is drawn; in this Manual, sampling frequency is quarterly, monthly, or weekly for period-based sampling, and is every day, every 2nd day, every 3rd day, every 4th day, every 5th day, and every 6th day for interval-based sampling.  For example, if your period-based sampling plan requires 10 service units per month, before the current month ends you must select at least 10 at random from the full list of all service units to be operated during the next month.

Sampling plan.  A plan for selecting service units at random, for collecting sample data, and for estimating annual service-consumed data that meets FTA’s 95% confidence and 10% precision levels.  Each sampling plan consists of four elements: a unit of sampling and measurement, a set of efficiency options, a sampling frequency, and a necessary sample size.

Sampling without replacement.  Selection of a sample of service units at random without the chance of a single service unit being selected more than once.

Sampling year.  Any report year for which you obtained annual UPT, annual PMT, or both through random sampling that meet FTA’s 95% confidence and 10% precision levels.  It can be a mandatory sampling year or an intermediate report year for which you choose to sample.

Service grouping.  One efficiency option for which you divide your service into two or more groups with the objectives of reducing within-group differences and increasing between-group differences.  For example, separating your bus routes into express routes and local routes is likely to reduce differences in average passenger trip length across one-way bus trips within each group.

Service unit.  An amount of revenue travel by a single transit vehicle, a set of transit vehicles, or a component of a transit vehicle.  For non-scheduled services, it is typically one vehicle day.  For scheduled bus services it is typically either a one-way bus run or else a round-trip bus run.  For rail services, it is either a one-way car run, a one-way train run, or a round-trip car run or a round-trip train run.

Statistical variation.  The degree of differences in a quantity across the full list of service units operated during a given duration of time, such as differences in PMT across all one-way trips of a bus service in a full report year.  A larger variation requires a greater sample size to meet given confidence and precision levels.

Table of random numbers.  A list of integers whose frequency and order of appearance in the list have been determined entirely by chance.  It is the basis of a commonly used method of random sampling.

Template sampling plan.  A sampling plan that is developed with the companion template of this Sampling Manual.

Unit of sampling and measurement.  A service unit you choose for your sampling plan.

§ 91.07 What do the reporting terms mean?

Auditable record.  Documentation of information collected and processes used in collecting that information that demonstrates your compliance with NTD requirements. Such documentation may also help quality control within your agency when your NTD staff change over time.

First-time reporting.  Reporting of a particular service to the NTD for the first time.

§ 91.09 What abbreviations for general terms are used in this Manual?

APTL.  Average passenger trip length in miles

APC.  Automatic passenger counter

FTA.  Federal Transit Administration

NTD.  National Transit Database

PMT.  Passenger miles traveled

PPMT.  Potential passenger miles traveled

UPT.  Unlinked passenger trips

§ 91.11 What abbreviations for NTD modes are used in this Manual?

CB.  Commuter bus – Fixed-route bus systems that are primarily connecting outlying areas with a central city. Service typically uses over-the-road buses with service predominantly in one direction during peak periods, limited stops, and routes of extended length.

CC.  Cable car – A railway propelled by moving cables located beneath the street. While popular at the turn of the last century, the only surviving system is operated in San Francisco.

CR.  Commuter rail – Rail service operating on either old freight railways, or on tracks that are shared with freight railways, Amtrak, or both. The service is characterized by relatively long distances between stops, for service primarily connecting a central city with outlying suburbs and cities. The service may be either diesel or electric-powered and usually has grade-crossings with roadways.

DR.  Demand response – Shared-ride demand response service is scheduled in response to calls from passengers. Many transit systems operate demand response (DR) service to meet the requirements of the Americans with Disabilities Act (ADA).

DT.  Demand response – Taxi – A special form of the demand response mode operated through taxicab providers. The mode is always purchased transportation type of service.

HR.  Heavy rail – An electric railway that operates local service in exclusive right-of-way. The service is characterized by long trains of six to eight cars or more and by relatively short distances between stops for local service within a city and the immediate suburbs. The Nation’s traditional subway systems are classified as heavy rail.

JT.  Jitney – A transit mode comprising of owner-operated passenger cars or vans operating on fixed routes (sometimes with minor deviations) as demand warrants without fixed schedules or fixed stops.

LR.  Light rail – An electric railway that operates local service in mixed traffic with road vehicles, or has grade crossings with roadways. The service is characterized by short trains of one to four cars and by relatively short distances between stops for local service within a city and the immediate suburbs.

MB.  Bus – Fixed-route bus service is the most-prevalent mode in the country. MB service is powered by a motor and fuel contained within a vehicle. Deviated fixed-route service is also reported as MB.

MG.  Monorail and automated guideway – An electric railway that straddles a single guideway. It may have vehicle operators or may use computers to guide the vehicles.

PB.  Público – Publicos are jitney services operated in Puerto Rico. A transit mode comprising of passenger vans or small buses operating with fixed routes but no fixed schedules. Publicos (PB) are a privately owned and operated public transit service which is market oriented and unsubsidized, but regulated through a public service commission, state or local government. Publicos (PB) are operated under franchise agreements, fares are regulated by route and there are special insurance requirements. Vehicle capacity varies from eight to 24, and the vehicles may be owned or leased by the operator.

RB.  Bus rapid transit – Fixed-route bus systems that either (1) operate their routes predominantly on fixed-guideways (other than on highway high occupancy vehicle (HOV) or shoulder lanes, such as for commuter bus service) or (2) that operate routes of high-frequency service with the following elements: Substantial transit stations, traffic signal priority or preemption, low-floor vehicles or level-platform boarding, and separate branding of the service. High-frequency service is defined as 10-minute peak and 15-minute off-peak headways for at least 14 hours of service operations per day. This mode may include portions of service that are fixed-guideway and non-fixed-guideway.

SR.  Streetcar rail – Rail systems operating routes predominantly on streets in mixed-traffic. This service typically operates with single-car trains powered by overhead catenaries and with frequent stops.

TB.  Trolleybus – Fixed-route service using rubber tire buses powered by electric current from overhead wires using trolley poles. Service using rubber tire replica trolleys or historic trolleys, powered by an on-board motor are not included in this mode.

TR.  Arial tramway – A system of aerial cables with suspended vehicles.

VP.  Vanpool – A commuting service operating under prearranged schedules for previously formed groups of riders in vans.

YR.  Hybrid rail – Rail systems primarily operating routes on the National system of railroads, but not operating with the characteristics of commuter rail. This service typically operates light rail-type vehicles as diesel multiple-unit trains (DMU’s).