§ 67.01 – What steps should I take after I have collected the sample data?

(a)    Design a format for recording your sample data.

(b)   Enter the raw data.

(c)    Process the entered data.

(d)   Identify errors in the entered data.

(e)    Identify sources of the data errors, if any.

(f)    Correct the data errors, if any.

(g)   What you should do within each step depends on your situation.  To be specific, the following example is used for the rest of this subsection:

(1)   you collect sample data with human ride checkers from one-way bus trips with designated stops,

(2)   you use the load-based approach to determining PMT,

(3)   you use predetermined between-stop distances, and

(4)   you have collected sample data from a route whose longest one-way trip is 4 miles.

§ 67.03 – What should I consider in designing the format for data recording?

(a)    The data items you have collected to determine PMT.  The exact data items depend on your service and the approach you have taken to determine PMT.

(b)   The data items that identify the service units in your sample.

(c)    A format that is easy for data analysis.

(d)   Suppose that you have designed a format in Table 67.01.  With this format, you enter the field data (7)-(14) as they appear on the field survey sheet shown in the filled-out form in Appendix 95.  Item (8) is not shown due to space limit.  The identification data items at the top of the survey sheet (1)-(6) are repeated for each stop of this one-way trip.

Table 67.01.  Example Format for Data Recording

Date

Day of Week

Time Period

Route No.

Trip No.

Direction

Stop Sequence

Distance to Next Stop

No. of Pass. Boarded

No. of Pass. Alighted

No. of Pass. On Board (Leaving Load)

No. of Pass. from Previous Trip (Stop 1 only)

No. of Pass. Continuing to Next Trip (Last Stop only)

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(9)

(10)

(11)

(12)

(13)

(14)

10/13/05

Thur

Midday

11

408

Outbound

1

0.3

20

0

20

2

 

10/13/05

Thur

Midday

11

408

Outbound

2

0.7

2

1

21

 

 

10/13/05

Thur

Midday

11

408

Outbound

3

0.6

0

2

19

 

 

10/13/05

Thur

Midday

11

408

Outbound

4

0.3

1

3

17

 

 

10/13/05

Thur

Midday

11

408

Outbound

5

0.5

1

10

8

 

 

10/13/05

Thur

Midday

11

408

Outbound

6

0.8

0

2

6

 

 

10/13/05

Thur

Midday

11

408

Outbound

7

0.2

0

1

5

 

 

10/13/05

Thur

Midday

11

408

Outbound

8

0.1

0

2

3

 

 

10/13/05

Thur

Midday

11

408

Outbound

9

0.1

0

2

1

 

 

10/13/05

Thur

Midday

11

408

Outbound

10

0.3

0

0

1

 

 

10/13/05

Thur

Midday

11

408

Outbound

11

0.1

0

0

1

 

 

10/13/05

Thur

Midday

11

408

Outbound

12

0.0

0

1

1

 

1

§ 67.05 – When should I enter my sample data?

(a)    You should have the sample data from each service unit entered immediately after your ride checker(s) has come back from the field.

(b)   This has a number of advantages:

(1)   reducing the chance of loss of information,

(2)   increasing the chance of correcting data errors, if any,

(3)   being ready to use the cumulative sample data any time during the sampling year, and

(4)   minimizing the rush at the end of the year.

§ 67.07 – How should I process the entered data?

(a)    You should process the data as follows immediately after you have entered them.  If your service unit has more than one one-way vehicle trip, you should process the data for individual one-way vehicle trips:

(1)   Sum the number of passengers boarded at individual stops in column (10) of Table 67.01 to get the total number of passengers boarded (UPT).  It is 24 in this case.

(2)   Sum the number of passengers alighted at individual stops in column (11) of Table 67.01 to get the total number of passengers alighted.  It is 24 in this case.

(3)   Calculate the load between every pair of two consecutive stops.  Table 67.03 shows an example and the formulas for calculating leaving loads and arriving loads.

(4)   Calculate PMT for each pair of consecutive stops by multiplying the calculated load with the between-stop distance.  Table 67.03 also shows the calculation of PMT with both leaving loads and arriving loads.

(5)   Calculate total PMT.  It is 47.8 miles in this case.

(6)   Divide total PMT by the total number of passengers boarded to get APTL.  It is 1.99 miles in this case.

(7)   Calculate vehicle trip length by summing up the predetermined between-stop distances in column (9).  It is 4.0 miles in this case.

(b)   If your sampling plan is based on the PPMT option, you should also process the data as follows immediately to calculate the ratio of PMT to PPMT for each service unit:

(1)   Calculate the average route length for each route.

(2)   Calculate PPMT by multiplying UPT by average route length.

(3)   Divide PMT by PPMT to get the ratio for each service unit.

(4)   Follow Subsection 85 on calculating average route length and PPMT.

Table 67.03.  Calculation of Loads and PMT

Load Type

Stop Sequence

Distance to Next Stop

No. of Pass. Boarded

No. of Pass. Alighted

No. of Pass. from Previous Trip

Calculated Load

PMT

Leaving Load

1

0.3

20

0

2

20

6.0

2

0.7

2

1

 

21

14.7

3

0.6

0

2

 

19

11.4

4

0.3

1

3

 

17

5.1

5

0.5

1

10

 

8

4.0

6

0.8

0

2

 

6

4.8

7

0.2

0

1

 

5

1.0

8

0.1

0

2

 

3

0.3

9

0.1

0

2

 

1

0.1

10

0.3

0

0

 

1

0.3

11

0.1

0

0

 

1

0.1

12

0.0

0

1

 

0

0.0

Total

4.0

24

24

2

N/A

47.8

Load for Stop 1 =

Current Boarding

 

Load for Other Stops =

Previous Load + Current Boarding – Current Alighting

Arriving Load

Stop Sequence

Distance from Previous Stop

No. of Pass. Boarded

No. of Pass. Alighted

No. of Pass. from Previous Trip

Calculated Load

PMT

1

0.0

20

0

2

0

0.0

2

0.3

2

1

 

20

6.0

3

0.7

0

2

 

21

14.7

4

0.6

1

3

 

19

11.4

5

0.3

1

10

 

17

5.1

6

0.5

0

2

 

8

4.0

7

0.8

0

1

 

6

4.8

8

0.2

0

2

 

5

1.0

9

0.1

0

2

 

3

0.3

10

0.1

0

0

 

1

0.1

11

0.3

0

0

 

1

0.3

12

0.1

0

1

 

1

0.1

Total

4.0

24

24

2

N/A

47.8

Load for Stop 1 =

0

 

 

 

 

Load for Other Stops =

Previous Load + Previous Boarding – Previous Alighting

§ 67.09 – How may I use the processed data to identify potential errors in the sample data?

(a)    Make sure that UPT and PMT are consistent for each service unit in the sample.  For example, they should both be zero or both be positive. 

(b)   Compare vehicle trip length with the longest actual length of the route.  Vehicle trip length must not exceed the longest route length.

(c)    Compare APTL with vehicle trip length and route length.  APTL must not exceed either.

(d)   Compare the total number of passengers boarded with the total number of passengers alighted.  They must be equal.

(e)    Examine the calculated load at the end point of the trip.  It must be zero for leaving loads.

(f)    If calculated, examine the PMT to PPMT ratio for each service unit.  It must not exceed 1.

§ 67.11 – How do I identify the sources of any errors?

(a)    If you have identified any error from the previous step, you should start with the calculations you did in processing the sample data to determine if an error is a calculation error or an error in the sample data.

(b)   Check if you have correctly calculated loads, UPT, PMT, and APTL.

(c)    Check if you have used between-stop distances and loads consistently:

(1)   If you use leaving loads, you must use the distance to the next stop.  The distance should be zero for the ending point of a one-way trip.

(2)   If you use arriving loads, you must use the distance from the previous stop.  The distance should be zero for the beginning point of a trip. 

(d)   Check the predetermined between-stop distances you entered.

(e)    Compare your calculated load with the observed load from the field.

§ 67.13 – How do I correct any errors?

(a)    Table 67.05 shows an example of sample data for a one-way trip where PMT is based on calculated leaving loads.  The first row of Table 67.07 shows the vehicle trip length, UPT, PMT, APTL, and the ratio of PMT/PPMT for this trip.

(b)   It has the following errors:

(1)   Vehicle trip length > route length.

(2)   APTL > route length.

(3)   Total boardings in column (10) < total alightings in column (11).

(4)   The load at the end stop < 0.

(c)    Error (b)(1) clearly indicates errors in the predetermined between-stop distances.  If you check what you have entered in column (9), you would notice the 7 miles from stop 3 to stop 4.  Correct the data-entry error by replacing 7 by 0.7.  After this change,

(1)   vehicle trip length matches the route length,

(2)   APTL becomes smaller than the route length, and

(3)   PMT is reduced to 34.7 with an APTL of 1.58 miles. 

(d)   To identify the source of error (3), compare the calculated loads with the observed loads.  You may notice that the calculated load is lower by 2 at the first stop.  It appears that the ride checker did not include the number of passengers from the previous trip in the number of boardings at the first stop.  With this correction,

(1)   Boardings become greater than alightings.

(2)   PMT is increased to 42.7 miles with an APTL of 1.78 miles.

Table 67.05.  Example of Correcting Data Errors

Stop Sequence

Distance to Next Stop

No. of Pass. Boarded

No. of Pass. Alighted

Observed Leaving Load

No. of Pass. from Previous Trip (Stop 1 only)

No. of Pass. Continuing to Next Trip (Last Stop only)

Calculated Leaving Load

PMT

(7)

(9)

(10)

(11)

(12)

(13)

(14)

(15)

(16)

1

0.0

18

0

20

2

 

18

0.0

2

0.3

2

1

21

 

 

19

5.7

3

7.0

0

2

19

 

 

17

119.0

4

0.6

1

3

17

 

 

15

9.0

5

0.3

1

9

8

 

 

7

2.1

6

0.5

0

2

6

 

 

5

2.5

7

0.8

0

1

5

 

 

4

3.2

8

0.2

0

2

3

 

 

2

0.4

9

0.1

0

2

1

 

 

0

0.0

10

0.1

0

0

1

 

 

0

0.0

11

0.3

0

0

1

 

 

0

0.0

12

0.1

0

1

1

 

1

-1

-0.1

Total

10.3

22

23

 

2

1

N/A

141.8

(e)    To identify why boardings are still larger than alightings, compare the recalculated loads with the observed loads again.  You may notice that the recalculated load starts deviating from the observed load at stop 5.  Since the calculated load is one passenger too big, increase the number of alighted passengers at stop 5 by 1 from 9 to 10.  With this correction,

(1)   Boardings equal alightings,

(2)   The leaving load at the end stop is 0, and

(3)   PMT is further reduced to 40.3 with an APTL of 1.68 miles.

(f)    You should also check the consistency between between-stop distances and the calculated loads.  Column (9) is based on the distance from the previous stop, but the calculated load is the leaving load.  Correcting this error leads to a final PMT of 47.8 with an APTL of 1.99 miles.

(g)   Table 67.07 also shows vehicle trip distance, UPT, PMT, APTL, and ratio PMT/PPMT for the cumulative corrections in (c), (d), (e), and (f).      

Table 67.07.  Impacts of Correcting Errors

Error Corrections

Vehicle Trip Length

PMT

UPT

APTL

PMT/PPMT

No corrections

10.3

141.8

22

6.45

0.63

§69.13 (c)

4.0

34.7

22

1.58

0.39

§69.13 (c) + (d)

4.0

42.7

24

1.78

0.44

§69.13 (c) + (d) + (e)

4.0

40.3

24

1.68

0.42

§69.13 (c) + (d) + (e) + (f)

4.0

47.8

24

1.99

0.50

§ 67.15 – What should I do if I fail to correct the data errors for a particular service unit?

(a)    You should treat the service unit as if it were missed for data collection.

(b)   You should follow the guidance in §65.29 for getting a replacement unit.

§ 67.17 – What steps should I take after I have identified and corrected errors in my data?

(a)    You should stack the corrected sample data from the field as shown in Table 67.01 in one or more worksheets.  These worksheets along with the survey sheets become an auditable record of your sample data.

(b)   You should enter the summary data at the level of your unit of sampling and measurement in a separate worksheet.  These summary data are ready for developing new sampling plans or for estimating service-consumed data for the NTD.

(c)    Table 67.09 shows how that summary worksheet looks with the column headings and the summary sample data for one service unit.

Table 67.09.  Example of Summary Sample Data

Date

Day of Week

Time Period

Route No.

Trip No.

Direction

Vehicle Trip Length

UPT

PMT

(1)

(2)

(3)

(4)

(5)

(6)

 

 

 

10/13/05

Thur

Midday

11

408

Outbound

4.0

24

47.8