Using an Odometer and a GPS Panel to Evaluate Travel Behaviour Changes Peter Stopher and Natalie...

Using an Odometer and a GPS Using an Odometer and a GPS Panel to Evaluate Travel Panel to Evaluate Travel

Behaviour ChangesBehaviour ChangesPeter Stopher and Natalie SwannPeter Stopher and Natalie Swann

Institute of Transport and Logistics Institute of Transport and Logistics StudiesStudies

The University of SydneyThe University of Sydneyand Camden FitzGeraldand Camden FitzGerald

Parson Brinkerhoff, SydneyParson Brinkerhoff, SydneyApril 2007April 2007

April 2007 Using an Odometer and a GPS Panel to Evaluate ...

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IntroductionIntroduction

Policies often aimed at changing travel behaviour

Rarely are the changes monitored to see if the policy was successful

Often the changes expected are within the error levels of self-report surveys


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A policy of major interest in Australia is Voluntary Travel Behaviour Change (VTBC or TravelSmart)

Based on improving household information about alternatives to current travel

Expectation is that it will result in reduced VKT by private car and possibly increased walk, bicycle, transit use, and car occupancy


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TravelSmart is a relatively cheap strategy compared to capital projects

Would be very cost-effective if it reduced car VKT by even 3-4 percent

Standard diary surveys have been shown to be in error by 20 percent or more on average

Self-reporting of distance travelled is potentially even more in error


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An Innovative An Innovative ApproachApproach

Use of panels to monitor changeMeasurement of the panel begins

prior to policy introductionPanel continues until some period

of time after introductionMethod one – quarterly odometer

surveyMethod two – annual or semi-

annual GPS survey


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Panels – recruit households who are asked to repeat the survey at prescribed intervalsAttrition – recruit additional

households in each wavePanel reduces error in measuring

changePanel members report changes in

demographics on each wave


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Odometer survey – request households to provide current odometer readings from each household vehicle and the date on which they take the reading

If a car is bought or sold, then beginning/ending odometer reading is requested and date of acquisition/sale

Readings are requested every quarter


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GPS survey involves carrying a GPS device for up to 28 days

Everyone over age 14 in household is asked to take a device

Survey is repeated either annually or semi-annually


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Three elements to the pilot evaluationQuarterly odometer panel of 200

households in South Australia and 200 in Victoria

Six-monthly 28-day GPS survey of 50 households in South Australia

Focus groups on participants in GPS panels

Six waves of the odometer panel completed

Two waves of GPS panel completedFocus Groups completed

Odometer Surveys


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Odometer PilotsOdometer Pilots

Six waves completed


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Odometer PanelsOdometer Panels

Response rates were as follows:Returned/Estimated Eligible

(%)W1 W2 W3 W4 W5 W6

SANew Recruit HHs 25.3 15.5 18.9 NA NA NA

Continuing HHs NA 89.8 88.1 90.6 90.1 89.8

VICNew Recruit HHs 17.8 19.5 NA 12.7 NA NA


Overall, similar patterns of recruitment and response in Melbourne and Adelaide


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Odometer Panels - Odometer Panels - Response Comparison Response Comparison

* These are all TravelSmart households

Negligible difference between 3 month and 4 month frequency

Returned/Estimated Eligible (%)

W1 W2 W3 W4 W5 W6

SA Main

New Recruit HHs 30.6 17.7 25.2 36.3 11.2* NA

Continuing HHs NA 90.1 91.6 92.3 88.7 NA

Add On SA

New Recruit HHs 25.3 15.5 18.9 NA NA NA


Add On VIC

New Recruit HHs 17.8 19.5 NA 12.7 NA NA



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Odometer Panels – Odometer Panels – Demographic Bias?Demographic Bias?

The demographic profile of the sample from wave to wave is remarkably stable.

There may be some coverage error, which can be corrected by applying weighting factors, but there does not appear to be any systematic non-response error.


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Odometer Panels – Odometer Panels – Elapsed Time – SAElapsed Time – SA

Attribute Waves 2-1

Waves 3-2

Waves 4-3

Waves 5-4

Waves 6-5

Waves 6-1

Elapsed Days 113.55 98.43 90.35 100.48 68.41 471.25

Standard Deviation in Days 31.77 11.38 9.27 11.17 6.44 32.43

No. of Valid Observations 260 308 331 318 321 207

No. Missing/Refused

66 (20%)

92 (23%)

104 (24%)

114 (26%)

116 (27%)

113 (35%)

Total No. of Vehicles

326 400 435 432 437 320


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Odometer Panels – Odometer Panels – Elapsed Time – Victoria Elapsed Time – Victoria

Attribute Waves 2-1

Waves 3-2

Waves 4-3

Waves 5-4

Waves 6-5

Waves 6-1

Elapsed Days 99.78 101.61 93.22 95.69 66.10 454.62

Standard Deviation in Days 35.29 13.22 11.02 10.48 12.06 34.01

No. of Valid Observations 274 262 272 279 282 235

No. Missing/Refused

97 (26%)

143 (35%)

129 (32%)

138 (33%)

140 (33%)

126 (35%)


371 405 401 417 422 361


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Odometer Panels – Odometer Panels – Average VKT – SA Average VKT – SA

AttributeWaves 2-

1Waves

3-2Waves

4-3Waves

5-4Waves

6-5Waves

6-1

Average Daily VKT 31.46 32.96 30.16 30.35 29.18 29.42

Standard Deviation

25.71 45.85 27.96 34.36 21.26 20.38

No. of Valid Observations

260 308 331 318 321 207

No. Missing/Refused

66 (20%)92

(23%)104

(24%)114

(26%)116

(27%)113

(35%)


326 400 435 432 437 320


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Odometer Panels – Odometer Panels – Average VKT –Victoria Average VKT –Victoria

AttributeWaves 2-

1Waves

3-2Waves

4-3Waves

5-4Waves

6-5Waves

6-1

Average Daily VKT 31.42 32.35 29.84 29.07 30.79 31.48

Standard Deviation

20.86 19.33 18.24 17.34 19.90 17.79

No. of Valid Observations

274 262 272 279 282 235

No. Missing/Refused

97 (26%)143

(35%)129

(32%)138

(33%)140

(33%)126

(35%)


371 405 401 417 422 360

Strong evidence of success in collecting Odometer readings– not Trip meter readings


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Odometer Survey - Odometer Survey - ConclusionsConclusions

Method works in both a small and large urban area

Response rates are higher than normal for a postal survey

Good evidence for successful reporting of Odometer readings and not trip-meter readings

The sample does not become more biased over time, although rotation of the panel may still be preferable.

GPS Surveys


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GPS PanelGPS Panel

Set up as 50 households in SA

Two waves conducted with 28-day task, six months apart

Third wave set up with 15-day task, six months later


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GPS PanelsGPS Panels

Panel Wave SA Panel (50)

Wave 1 Wave 2 “Wave 3”

Recruited (New to the wave) 57 17 0

Completed 50 14 0

Continuing (Recruited) 35 44

Continuing (Completed) -- 32 36

Total Complete Households 50 46 36

Households Failing to comply 4 (8%) 4 (9%) 1 (3%)


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GPS Panels – Days of GPS Panels – Days of Data by PersonData by Person

Number of Days Wave 1 Pilot Panel

(50)

Wave 2 Pilot Panel (46)

All Days 1 (1%) 39 (44%)

Up to 6 days per week 13 (12%) 21 (24%)

5 to less than 6 days 10 (10%) 7 (8%)

3 to less than 5 days 27 (25%) 8 (9%)

1 to less than 3 days 32 (30%) 9 (10%)

More than 0 and less than 1 24 (22%) 5 (6%)

Total 107 89 (100%)


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GPS Survey AnalysisGPS Survey Analysis

Analysis has been done at several levelsDisaggregate – person by dayAggregated to days of the weekAggregated to personsAggregated further to households

In wave 2, some households overlapped the Easter HolidaysPerson days that appeared to have

extensive travel on one or two days in the period were dropped from disaggregate analysis


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GPS Panel – Trip Data GPS Panel – Trip Data Per Person DayPer Person Day

Statistic (sd in brackets)

Wave 1 Panel Wave 2 Panel*

All Days

Week-days

Week-ends

All Days

Week-days

Week-ends

Number of Valid Obs. 1571 1116 455 1968 1397 571

Mean Number of Trips 3.85(3.44)

3.64(3.30)

4.35 (3.71)

3.80 (3.74)

3.68 (3.71)

4.07 (3.80)

Mean PKT 25.6(33.0)

24.1(31.79)

29.2 (35.5)

25.8 (36.36)

25.0 (34.37)

27.6 (40.81)

Mean Travel Time 55.3(51.6)

53.0 (50.36)

60.8 (54.10)

50.6 (52.24)

49.8 (51.89)

52.7 (53.08)

* 4 households were found to have undertaken excessive (probably holiday) travel on two or more days around the Easter period in 2006 and were excluded from these statistics


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GPS Panel – Trip Data GPS Panel – Trip Data Per Person by Day of Per Person by Day of

WeekWeekStatistic (sd in brackets)

Wave 1 Panel Wave 2 Panel

All Days

Week-days

Week-ends

All Days

Week-days

Week-ends

Number of Valid Obs. 509 364 145 551 394 157

Mean Number of Trips 3.96(2.37)

3.77(2.22)

4.44 (2.65)

3.99 (2.61)

3.90 (2.59)

4.21 (2.62)

Mean PKT 25.0(22.73)

23.3(22.49)

29.2 (22.86)

29.3 (37.96)

28.7 (40.15)

30.8 (31.86)


52.2 (37.26)

61.5 (39.59)

51.8 (41.85)

51.0 (42.30)

54.0 (40.73)

Note that even the large values are included in Wave 2.


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GPS Panel – Trip Data GPS Panel – Trip Data Per Person by Day of Per Person by Day of

WeekWeek

Note that even the large values are included in Wave 2.


Wave 1 Panel Wave 2 Panel Wave 1-Wave 2 Covariance

All Days All Days All Days

Number of Valid Obs.

79 73 42

Mean Number of Trips

3.91(1.77)

3.96 (1.58)

1.66

Mean PKT 24.7(15.80)

25.0 (14.76)

69.6


54.7(24.45)

246.4


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GPS Panels – Trip GPS Panels – Trip Data Per HouseholdData Per Household


Wave 1 Pilot Panel

Wave 2 Pilot Panel

Wave 1-Wave 2 Covariance

All Days All Days All Days

Number of Valid Obs. 41 43 28

Mean Number of Trips per person

4.06(1.50)

3.94 (1.64)

2.11

Mean PKT 24.8(14.03)

24.3 (12.52)

92.1


47.8 (20.70)

273.3


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GPS DurationGPS Duration

Panel Survey suggests that:Recruitment rates are not affected much

between 7 and 28 daysAlso, early drop out is not much affected

by the length of GPS recordingStatistics tend to stabilise after about 10-

12 daysWe have determined that there is no halo

effect in the first few days

Ideal appears to be a 15-day GPS


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GPS FrequencyGPS Frequency

Attrition for three waves of the six-monthly GPS was not markedly different than for two waves of the annual GPS survey

Annual participants have received interim mailings

Non-compliance rate is about double in the annual survey (8% versus under 4%)

Focus Groups


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Focus Groups - ThemesFocus Groups - Themes

Six themes were derived from the group discussions:

1. Respondents’ understanding of the survey task;

2. The form and functions of the devices;

3. Patterns of respondent behaviour in undertaking the task;

4. Reactions to the survey documents and survey administration;

5. Respondent attitudes and perceptions of issues relevant to the study; and

6. Curiosities about the study displayed by respondents.


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Focus Groups - Focus Groups - OutcomesOutcomes

Newsletter- to encourage and educate respondents

Sourcing new devices – to improve performance

Refining survey documentation – to further clarify the GPS task


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ConclusionsConclusions

Both panel surveys are feasible methods Odometer survey can show small

differences in average VKT with suitable sample sizes

GPS survey can provide a much greater wealth of data on effects of the policy

Other work shows much smaller sample sizes are required for GPS versus Odometer

Using an Odometer and a GPS Panel to Evaluate Travel Behaviour Changes Peter Stopher and Natalie...

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