Weighting Waiting: Evaluating the Perception of In-

Vehicle Travel Time Under Moving and Stopped Conditions

David LevinsonKathleen HarderJohn Bloomfield

Kasia Winiarczyk

Issue

• Drivers prefer unobstructed traveling conditions. However when there is significant traffic, traffic engineers can allow the delay to occur on the freeway, or can control entrance to the freeway with ramp meters, and put the delay there (generally with some overall performance gains).

• However ramp meters, used on over 400 freeway ramps in Twin Cities were quite controversial, leading to an 8-week shutdown and a revamping of the control strategy.

Study

• Use driving simulator (AutoSim) to determine if ramp wait is preferred to unmetered traffic.

• We call this Virtual Experience Stated Preference (VESP).

• Contrast with more traditional Computer Administered Stated Preference (CASP).

• Conditions nominally identical between the two. Want to see if the results are similar.

Subject Selection

• List of University of Minnesota employees, excluding faculty. We exclude those outside of Minneapolis, those in Dept. of Civil Engineering, and those who were contacted for pilot.

• CASP: Randomly email 1308 persons. 209 replied. Non-drivers excluded. 89 were scheduled, but 15 were no-shows. Leaving 74 subjects, of which 5 were non-drivers anyway. 69 valid observations

• VESP: Randomly emailed subjects (excluding those contacted previously), similar process, -> 42 participants. 4 were ill, 6 faced software bugs or crashes (vehicles driving through other vehicles). -> 32 good observations.

CASP VESPFEMALEMALE FEMALEMALE

Number 41 21 16 19Age Mean 41.4 45.1 37.7 35.3(Years) Std. Dev. 11.3 10.9 10.8 8.7AutoOwnership Mean 2.3 2.3 2.2 2.3Number Std. Dev. 1.2 1.3 0.8 1.2Commute Time Mean 19.6 15.5 14.0 19.9(Minutes) Std. Dev. 27.3 11.2 10.4 13.1Housing Type Single-Family 73% 81% 63% 79%

Multi-Family 27% 19% 38% 21%Household Mean 1.3 1.2 2.4 2.8Size Std. Dev. 0.4 0.4 1.0 1.4

Descriptive Statistics

Computer Administered Survey

• Subjects mailed travel diary and asked to complete it day before coming in for interview.

• Computer-based instrument, includes: demographic/socio-economic questionnaire, transportation attitude survey, personality survey.

• In addition CASP subjects asked to rate and rank scenarios presented in choice conditions.

• VESP subjects would then use driving simulator.

Driving Simulator (In Preparation)

Simulator: Driver’s Perspective

Hypotheses

• CASP subjects will respond similarly to VESP subjects. If this is borne out, we can use CASP with confidence that it replicates the more expensive VESP studies.

• Ramp time is more onerous than freeway time. This is consistent with transit studies that have shown that wait is more onerous than in-vehicle time.

Choice Conditions

Ramp Wait Drive Time Speed

Condition min min mph (km/hr)A 0 20 30 (48)B 2 15 40 (64)C 4 12 50 (80)D 6 10 60 (96)

Utility

• U = f(R,F,S,T)• R = ramp wait (min)• F = freeway travel time (min)• S = sex (1 if male, 0 otherwise)• T =reported daily commute time

Rank-Order Logit Model of CASP

Model 0 Model 1 Model 2 Model 3β z P>|z| β z P> |z| β z P> |z| β z P> |z|

R+F 0.0178 0.33 0.74R/F -1.61 -3.94 0.000R -1.561 -6.31 0.000 -1.404 -5.40 0.000F -0.816 -5.77 0.000 -0.828 -5.79 0.000S*F -0.121 -1.93 0.053 -0.127 -2.00 0.045R/T -4.681 -1.65 0.100(Obs,groups) (192,48) (192,48) (192,48) (192,48)Log likelihood -152.49 -144.141 -125.406 -123.989LR chi2 0.11 16.81 54.28 57.12Prob > chi2 0.74 0.00 0.00 0.00

CASP Results: Ranks

Relationship between ramp wait and utility

1.00

2.00

3.00

4.00

0 5 10 15 20

Ramp wait (min)

Average Rank

rank A-D

rank Ax2-Dx2

rank Ax3-Dx3

rank E-H

CASP Results: Ratings

Relationship between ramp wait and utility

00.5

11.5

22.5

33.5

44.5

0 2 4 6 8

ramp wait (min)

Average Rating

scale A-D

scale E-H

Rank-Order Logit Model of VESP

Model 0 Model 1 Model 2 Model 3β z P>|z| β z P> |z| β z P> |z| β z P> |z|

R+F -0.416 -4.64 0.00R/F 4.432 6.21 0.000R 0.753 2.58 0.010 0.759 2.29 0.022F 0.219 1.32 0.187 0.203 1.16 0.247

S*F -0.813 -1.33 0.182 -0.064 -1.03 0.301R/T -0.496 -0.21 0.835(Obs, groups) (124,31) (124,31) (124,31) (112,28)Log likelihood -84.029 -73.833 -72.987 -66.473LR chi2 28.98 49.37 51.06 45.02Prob > chi2 0.0000 0.0000 0.0000 0.0000

Comparison of Methods: Recency

• CASP presents all information (ramp time, freeway time) simultaneously and asks for a rating and ranking.

• VESP presents experience/information sequentially (ramp wait before freeway travel) and aks for rating.

• Test: conduct VESP experiments with the wait at the end

Sequence

• Simultaneous vs. Sequential comparison

• CASP presents information in components and presented simultaneously

• VESP presents a fluid trip, making direct comparison more difficult.

• Test: Present CASP information differently somehow …

Public Opinion

• Ramp meters have been widely discussed in media.

• CASP respondents may have responded negatively to ramp wait as an idea, without thinking about the alternative stop-and-go conditions

• Test: Remove study in time more from present, conduct in different place

Intensity of Stop-and-Go

• Simulated stop-and-go may be worse than reality. VESP may be worse case, while in CASP people recalled typical case

• Test: Revise, better calibrate, simulator

Goal-Direction

• In normal conditions, drivers have a purposeful goal that has meaning. In the VESP, the goal was entirely artificial.

• Stop-and-go in which a goal is slowly being reached my differ from stop-and-go without a goal, the latter may be more annoying.

• Test: Introduce goal (time based) into VESP, e.g. $10 if you make it in a certain time.

Experimental Artifact

• VESP may be uncomfortable, especially with stop-and-go. 4 of 42 subjects had to leave the experiments due to simulator sickness, others may have completed the experiment and been uncomfortable.

• Test: for successful subjects ask for comparison of simulator to real driving. A test suggests there is no statistical difference between the subjects completing this experiment and those completing another recent experiment where no subjects were ill.

Conclusions

• Compared Computer Administered Stated Preference with Virtual Experience Stated Preference to ascertain value of time at ramps vs. stop-and-go traffic.

• CASP suggests time at ramp meters is 1.6 - 1.7 times more onerous than driving in stop-and-go conditions.

• VESP suggests the opposite: a minute of stop-and-go is 3-4 times more onerous than ramp meter wait

Further Research

• Determine what is more correct, use real world results.

• Issues with SP methods, and how information is presented vs. experienced

• People experience the world subjectively, we need to be able to measure this subjective perception as accurately as possible.