Preliminary Analysis of Key Variables

There are many variables related to travelers’ demographics and general travel characteristics which influence their travel behavior. These key variables thus play an important role in estimation of the mode choice models. Descriptive statistics for these variables are presented in Table 9. The descriptive statistics can be used to check the presence of outliers and invalid responses. This analysis can also be used to gauge the general characteristics of the sample respondents.

Table 9 Descriptive Statistics for Important Variables

Variable Mean

Std.

Dev. Min Max Variables Related to General Travel

Number of people in the vehicle during the last trip 1.55 0.91 1 5 Trip length (miles) for the last trip 13.43 7.35 0.6 31 Traveled toward downtown Houston for last trip (dv) 0.48 0.50 0 1 Last trip was a trip that the traveler regularly takes (dv) 0.56 0.50 0 1 Traveler has an option of taking an alternative route (dv) 0.76 0.43 0 1 Respondent had heard about the new Katy managed lanes

before taking the survey (dv) 0.86 0.34 0 1

Respondent’s trip purpose was commute or work for the last

trip on Katy Freeway (dv) 0.56 0.50 0 1

Respondent possesses a toll tag (dv) 0.95 0.21 0 1

Respondent needs to pay to park in downtown (dv) 0.14 0.35 0 1 Number of trips on Katy Freeway in last week 4.32 4.18 0 26 Respondent's last trip was on a weekday (dv) 0.82 0.38 0 1 Respondent traveled in peak period (6.00 a.m.-9.00 a.m. or

3.30 p.m. to 6.30 p.m.) for last trip (dv) 0.52 0.50 0 1 Demographic Variables

Number of vehicles in household 2.40 1.07 0 10

Male respondent (dv) 0.58 0.49 0 1

Respondents age between 25 and 54 years (dv) 0.71 0.45 0 1 Respondents annual household income between $50,000 and

$99,000 (dv) 0.37 0.48 0 1

Respondents annual household income over $100,000 (dv) 0.50 0.50 0 1

Respondents household size 2.73 1.32 0 9

Respondents household type is a single adult household (dv) 0.19 0.39 0 1 Respondent's household type was married (dv) 0.27 0.44 0 1 Respondent's household type was married with children (dv) 0.45 0.50 0 1 Respondent's occupation was technical (dv) 0.09 0.29 0 1 Respondent’s occupation was professional (dv) 0.52 0.50 0 1

Respondent's occupation was sales (dv) 0.07 0.26 0 1

Respondent's occupation was administrative/ clerical (dv) 0.08 0.27 0 1 Respondent's education was less than high school graduation

(dv) 0.00 0.05 0 1

Respondent was a high school graduate (dv) 0.05 0.22 0 1 Respondent completed some college or vocational school (dv) 0.25 0.43 0 1 Respondent had a post graduate degree (dv) 0.22 0.42 0 1 dv- dummy variable

Further, in order to gain insight into travel behavior of travelers who drove alone and travelers who carpooled for their last trip on the Katy Freeway they were analyzed separately. This comparison is shown in Table 10. These two groups significantly differ based on some of the characteristics which are highlighted in the Table 10. These differences are as expected because travelers are more likely to carpool if they are traveling in off-peak hours, on weekend, for longer trips, for trips related to other than commuting or work, and are married with children. Note that the mean of a dummy variable corresponds to the percentage of respondents in that category.

Table 10 Comparison of Respondents Who Drove Alone and Those Who Carpooled

Variable DA CP

Mean of Variables Related to General Travel

Number of people in the vehicle during the last trip 1.00 2.54 Trip length (miles) for the last trip 12.74 14.63 Traveled toward downtown Houston for last trip (dv) 0.48 0.46 Last trip was a trip that the traveler regularly takes (dv) 0.63 0.42 Traveler has an option of taking an alternative route (dv)* 0.76 0.75 Respondent had heard about the new Katy managed lanes

before taking the survey (dv) 0.87 0.85

Respondent’s trip purpose was commute or work for the last

trip on Katy Freeway (dv) 0.70 0.32

Respondent possesses a toll tag (dv) 0.96 0.94

Respondent needs to pay to park in downtown (dv)* 0.14 0.14 Number of trips on Katy Freeway in last week* 4.89 3.31 Respondent's last trip was on a weekday (dv) 0.90 0.67 Respondent traveled in peak period (6.00 a.m.-9.00 a.m. or

3.30 p.m. to 6.30 p.m.) for last trip (dv) 0.55 0.46 Mean of Demographic Variables

Number of vehicles in household* 2.37 2.46

Male respondent (dv) 0.59 0.56

Respondents age between 25 and 54 years (dv) 0.71 0.72 Respondents annual household income between $50,000 and

$99,000 (dv)* 0.37 0.37

Respondents annual household income over $100,000 (dv)* 0.50 0.50

Respondents household size* 2.65 2.87

Table 10 (Continued)

Variable DA CP

Respondents household type is a single adult household (dv) 0.23 0.12 Respondent's household type was married (dv) 0.26 0.28 Respondent's household type was married with children (dv) 0.41 0.51 Respondent's occupation was technical (dv)* 0.09 0.09 Respondent’s occupation was professional (dv) 0.55 0.46 Respondent's occupation was sales (dv) 0.08 0.05 Respondent's occupation was administrative/ clerical (dv) 0.07 0.09 Respondent's education was less than high school graduation

(dv) 0.00 0.00

Respondent was a high school graduate (dv) 0.05 0.06 Respondent completed some college or vocational school (dv) 0.25 0.26 Respondent had a post graduate degree (dv) 0.23 0.22 DA- Respondents who drove alone for last trip,

CP- Respondents who carpooled for last trip, dv- dummy variable

*- Group means (or proportions) are not significantly different at 95% confidence level

The above traveler groups were separated based on their general travel

characteristics; however it is also possible to gain some understanding of travel behavior by comparing the SP survey responses. Accordingly, the respondents who selected a ML lane alternative in at least one of the SP questions were compared to the respondents who didn’t select any of the ML travel alternatives in any of the SP questions (Table 11).

This comparison can be helpful in studying who will be interested in using the MLs. It can be observed from Table 11 that travelers in both categories have similar

characteristics. However, travelers who are on longer trips, who traveled in peak hours, who are married and have children (household type), who are professionals by

occupation are more likely to chose the MLs.

Table 11 Comparison of Respondents Who Selected MLs and Those Who Never Selected MLs in Any of The SP Questions

Variable Mean of Variables Related to General Travel

Number of people in the vehicle during the last trip 1.64 1.33

Trip length (miles) for the last trip 13.84 12.43

Traveled toward downtown Houston for last trip (dv)* 0.47 0.48 Last trip was a trip that the traveler regularly takes (dv)* 0.55 0.56 Traveler has an option of taking an alternative route (dv) 0.77 0.73 Respondent had heard about the new Katy managed lanes before

taking the survey (dv) 0.86 0.86

Respondent’s trip purpose was commute or work for the last trip (dv)* 0.56 0.57

Respondent possesses a toll tag (dv) 0.96 0.94

Respondent needs to pay to park in downtown (dv) 0.15 0.12

Number of trips on Katy Freeway in last week 4.26 4.46

Respondent's last trip was on a weekday (dv) 0.81 0.84

Respondent traveled in peak period (6.00 a.m.-9.00 a.m. or 3.30 p.m.

to 6.30 p.m.) for last trip (dv) 0.58 0.38

Mean of Demographic Variables

Number of vehicles in household 2.37 2.46

Male respondent (dv) 0.59 0.56

Respondents age between 25 and 54 years (dv) 0.71 0.72

Respondents annual household income between $50,000 and $99,000

(dv) 0.37 0.37

Respondents annual household income over $100,000 (dv)* 0.50 0.50

Respondents household size 2.65 2.87

Respondents household type is a single adult household (dv) 0.23 0.12

Respondent's household type was married (dv) 0.26 0.28

Respondent's household type was married with children (dv) 0.41 0.51

Respondent's occupation was technical (dv) 0.09 0.09

Respondent’s occupation was professional (dv) 0.55 0.46

Respondent's occupation was sales (dv)* 0.08 0.05

Respondent's occupation was administrative/ clerical (dv) 0.07 0.09

Respondent was a high school graduate (dv) 0.05 0.06

Respondent completed some college or vocational school (dv) 0.25 0.26

Respondent had a post graduate degree (dv)* 0.23 0.22

dv= dummy variable, * - Group means/ proportions are not significantly different (95% Conf. level)

The data related to SP questions were further analyzed to verify if the survey logic was implemented as expected during the data collection (Table 12). The summary of SP choices (ignoring the unanswered SP questions) is also presented in Table 12. It can be observed that ‘driving alone on GPLs’ is the most preferred mode of the

respondents and in urgent trips more respondents tend to switch from the GPLs to MLs.

The analyses carried out in this section thus provided useful information related to sampling issues. The descriptive analysis provided summary of important variables for the whole sample and traveler groups. This information was used for the model building in the next section. The next section is focused on detailed analysis for investigating the survey designs and the effect of travel urgency on VTTS.

Table 12 Preliminary Analysis of Data Related to SP Questions

Percent of Times the Alternative was Presented to The Respondent

In first pair of SP questions 23% 22% 20% 15% 20% 100%

In second pair of SP

questions 23% 20% 19% 20% 18% 100%

In third pair of SP questions 23% 14% 23% 21% 18% 100%

In all SP question pairs 23% 19% 21% 19% 18% 100%

VTTS ($/hr) Presented for the Alternative in All the Three Pairs of SP Questions

Mean NA NA 21.9 11.3 3.3 NA

Std. Dev NA NA 16.6 12.2 5.4 NA

Minimum NA NA 0.0 0.0 0.0 NA

Maximum NA NA 285.0 216.0 108.0 NA

Percent of Times the Alternative was Selected

In an ordinary situation 60% 9% 17% 9% 5% 100%

In a urgent situation 46% 6% 33% 11% 4% 100%