Transcript nnecting Travel Survey & Travel Issues - Home

Household Travel Surveys
Lessons / Issues / Plans
Presentation
to the
AMPO Travel Modeling Working Group
October 24, 2006
Ron Milone
MWCOG/NCRTPB
Washington, DC
1
Dynamics shaping the planning process in
the Washington, DC region
•
Sprawling development continues
– The Washington region is second to New York for the percentage of
workers with "extreme commutes”
–
•
Home buyers trade off lower housing prices with longer commutes
Public money for new construction limited
– Local share of funding for transportation costs is increasing
•
Virginia is considering public-private partnership for building HOT lanes
– Managed highway pricing is planned in Maryland
•
The number of immigrant residents/workers has increased, helping to
counter the number of baby boomers who are retiring
•
Extensions to the completed 103-mile Metrorail system now planned.
Increasing transit service and ‘Smart Growth’ are cited by many as
congestion remedies
2
Why are HH surveys conducted?
• Sample measurements: Household travel
surveys are intended to identify localized
relationships between travel ‘desires’ and land
use, system, policy factors that can be
forecasted
• Household travel surveys are not designed to
count demographic and travel quantities with a
high level of geographic precision.
3
The HH survey is one component of a
regional inventory that informs models
Inventory of the transport system
(past / present / future)
Networks
Inventory of activity pattern
(past / present / future)
Land Use
Inventory of system use
Highway Counts / Transit
Counts (OB surveys)
HH Travel Survey
Inventory of residential demand:
Inventory of non-resident travel markets
External, Truck, Taxi,
Workplace, Airport, etc.,
Surveys
4
What are the key products?
(with respect to modeling)
Household File
Person File
Vehicle File
Trip File
Size
Age
Model
Origin Purpose
Income
Gender
Make
Dest. Purpose
Vehicles
Emp. Status
Type
Primary Mode
Workers
No. of Jobs
Year
Sub modes
Dwelling Type
Driver Status
Fuel
Passengers
Owner/Renter
Worker type
Miles Driven
Travel Costs
(Park/Fare/Toll)
Starts
Begin Time
Stops
End Time
Bicycles
5
Needs of conventional modelers
• Trip Rates, by purpose
– Production-end rates
– Attraction-end rates
• Trip Length Frequencies, by purpose, by
O-D pattern
• Modal Share, by purpose, by O-D pattern
• Time-of-Day profile by purpose, by mode,
by directionality
6
How low can the surveys go, with
confidence?
• Regional level - Yes
• Regional Level,
by socio-economic stata -Yes
• State Level - Probably
• County Level – Maybe
• By Sector – Maybe/No
• By TAZ or finer- No
7
Organizational Issues
• A HH survey is a substantial, yet infrequent
undertaking; it can be a ‘shock-wave’ to the work
program
• Identifying funding sources is a challenge
• The knowledge/skills requirements are unique
• Administration of survey is increasingly being outsourced – How well do surveyors know the region?
• Interagency cooperation and coordination required
• Interfacing with the general public is always a delicate
matter
8
Past HH Travel Surveys in
Washington, DC
• 1968 Home Interview Survey
– Face-to- Face Interviews with an ‘army’ of interviewers
– 26,000 Households sampled (1 in 20, 1 in 33)
– 6 Jurisdictions
• 1987/88 Home Interview Survey
– Mail / CATI combination (conducted by MPO)
– 8,000 Households sampled (1 in 166)
– 8 Jurisdictions
• 1994 Spring/Fall Home Interview Survey
– Mail / CATI combination (conducted by consultant)
– 4,800 Households sampled (1 in 300)
– 13 jurisdictions
9
Trends Impacting Surveys
•
•
•
•
Study area is steadily expanding
Cost of data collection is increasing
Sample sizes are steadily decreasing
Ability to collect data by telephone- increasingly difficult
– Cell phone market share increasing
– Telephone ‘land line’ market share decreasing
– Telephone screening technology improving
•
•
•
•
Modeling requirements/complexity is increasing
Policy questions being asked are ahead of tools
Surveys, in general, are saturating the area
Privacy, confidentiality, and identity theft are growing
concerns
10
Essential HH Survey Goals
• Appropriate capture and selection of HHs
– representation of socio-economic markets
– adequate capture of the ‘minority’ modes
•
•
•
•
Minimizing non-response
Minimizing under-reporting of travel
Maximizing Location Accuracy
Data that’s valid and ‘clean’
11
Survey Implementation Process
• Planning
• Survey Design
– Assemble background data: Census STF1-4, CTPP, PUMS
– Formulate survey approach, sampling procedures,
– Design instrument(s)
• Field Implementation
– Pretesting, data collection
• Data Preparation
– Coding, cleaning, compiling
• Data Analysis
– Analyzing, Reporting, Using
12
Non-Response
• The main concern: bias in the data
• Response rate for 1994 HTS: 38%
– 50 % Recruitment: unusable telephone numbers: fax
machines, nonresident units, unoccupied units, etc.
– 76% Retrieval: refusals, no telephone contact made, language
problems, <50% HH members responded.
• Who are non-responders?
–
–
–
–
Low income groups
Telephone ‘screeners’
People who just are not home: high mobility groups!
People who are home, but do not travel – They don’t feel
‘applicable’ to a travel survey
• Item non-response: income, age
13
How to Deal with Non-Response
• HH non-reponse:
– Ignore it (if sample size is sufficient without nonrespondents)
– Assumption: Non-respondents are similar to
respondents (!)
• Item non-response:
– Impute values (Hot Decking)
– Is a reasonable fix if the non-respondent population is
different from respondent population
– ‘Nearest-neighbor’ approach – uses like socioeconomic and personal characteristics to ‘fill in’ item
non-response and to adjust trip weights
14
Data Cleaning
logical, rational, and reasonable models require like data
Question: How much time/effort is needed
to clean data?
Answer: How much time do you have?
• 1994 HTS: 1.5 -2.0 person-years
• What’s involved (cleaning HH/Trip/Person files):
– one-way Frequencies – range/distribution
– Cross-tabulations: logical /consistent/coherent
– Trip-chaining: logical timing & sequence of trip
itinerary
– Address Matching: the big one
– Validating against other data sources
15
Plans: 2007 Household Travel Survey
• Project Director: Robert Griffiths,
Technical Services Director, COG/TPB
• Travel and Activity Survey – 10,000 HH
• In-Vehicle GPS add–on – 250 households
• Planned Survey Design
– Address – based sample from USPS carrier route lists, as
opposed to Telephone/Random-Digit-Dial(RDD)-based
• Circumvents telephone-related issues cited above
• Better control of uniform geographic capture, that is not ensured
using RDD method
• Differential sampling rates by area type
• All households with deliverable mail address in sample, except
those on ‘do-not-mail’ list (3%)
16
Sampling
• 22 jurisdictions (modeled area)
• Frame – mail carrier routes
• Segmentation:
– ‘Inner Ring‘ Jurisdictions
• High density/mixed use areas (over-sampled to
ensure capture of ‘minority’ modes (transit, ride
share, walk, bicycle)
• Low Density areas
– ‘Outer Ring’ Jurisdictions
17
Data Collection
• Initial mailing
– Minimal household, person, vehicle
characteristics asked
• Follow-up telephone recruitment
• Telephone/Internet travel-activity data
retrieval (respondent’s option)
• Real-time geocoding used
18
Pilot Test (in progress)
• Assessing coverage of proposed mail
route sample as opposed to RDD sample
• Assessing the effect of financial incentives
• Assessing interview method response
rates
• Testing conversion methods for nonrespondents / non-response follow-up
survey
19
Pilot Test … continued
• Vehicle GPS add-on survey will be tested
– will be used to assess under-reporting or overreporting of trip making.
• The assignment of “observed’ vehicle trips from the survey
has historically resulted in an under-estimation of VMT.
• Short non-work trips are typically under-reported, and so trip
rates are usually increased to make up for the difference.
• Is this the right thing to do? Other possible sources of error:
– Commercial Vehicle trips not well reflected
– External trips not well reflected
– Error in Observed VMT
20
Schedule
• Pilot Test Evaluation: Now
• Main Survey: November 2006 – January
2008
– Survey will be collected throughout the 13
month period.
21
22
Conclusions on HH Surveys
• Vital for formulating variable relationships
in the work
• But one piece of the data puzzle
• Typically lag behind the questions being
asked
• Subject to problems relating to nonresponse, under-reporting, geographic
coverage, modal coverage
23
Conclusions …
• Modelers should be involved at the ‘frontend’ of survey design & development
– Is the information obtained appropriate?
– Are questions asked in the best way?
– What are the limitations of the survey?
• Sources of error abound, data is imperfect
• Technology must continually be exploited
to address issues
24
Read more about the Washington
Household Travel Survey
www.mwcog.org/hts
25