A hybrid speed choice model: the role of human factors

Figures & data

Figure 1. A hybrid speed choice and latent variables framework.

Figure 2. Normal Q-Q plot of speed.

Table 1. Descriptive statistics of the sample

Variable
Age	Mean = 41.8	SD = 14.6
Age < 25 years old	Yes = 17.64% (181)	No = 82.36% (845)
Age between 25 and 40	Yes = 30.79% (316)	No = 69.21% (710)
Agebetween 40 and 60	Yes = 35.96% (369)	No = 64.04% (657)
Age > 60	Yes = 15.61% (160)	No = 84.39% (866)
Gender	Male = 72.02% (379)	Female = 27.98% (287)
Well educated (holding university degrees)	Yes = 28.84% (296)	No = 71.16% (730)
Experienced driver (> 10 years old)	Yes = 69.98% (718)	No = 30.02% (308)
Expensive car (> 300 million Toman*)	Yes = 36.74% (377)	No = 63.26% (649)
Speed	Mean = 111.01	SD = 13.55
Slow driving group	Yes = 33.82% (347)	No = 66.18% (649)
Speed limit range	Yes = 48.05% (493)	No = 51.94% (533)
Fast driving	Yes = 18.13% (186)	No = 81.87% (840)

*One US Dollar was 11,840 Tomans in August 2019.

Table 2. Statistics of the TPB items

Item	Mean	SD
Attitudes (ATT)
‘For me to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months would be’: harmful/beneficial	5.76	1.21
‘For me to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months would be’: unpleasant/pleasant	5.72	1.09
‘For me to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months would be’: bad/good	5.89	1.26
‘For me to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months would be’: not acceptable/acceptable	5.78	1.18
Subjective norm (SN)
‘I think people who are important to me want me to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months’: agree/disagree	6.02	1.16
‘I think people who are important to me think I should not/think I should comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months’: agree/disagree	5.98	1.07
‘People who are important to me approve/disapprove of me exceeding the speed limit 120 km/h in freeways over the next 3 months’: agree/disagree	6.08	1.12
Perceived behavioral control (PBC)
‘For me to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months would be’: very difficult/very easy	4.37	1.20
‘How confident are you that you will be able to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months?’: not very confident/very confident	4.41	1.18
Intention (INT)
‘Do you intend to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months?’: definitely do not/definitely do	4.84	1.15
‘How much do you want to comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months?’: not at all/very much	4.87	1.19
‘How likely is it that you will comply with the speed limit range of 100 km/h to 120 km/h in freeways over the next 3 months?’: very unlikely/very likely	4.81	1.21

Note. All items were measured by a seven-point Likert scale

Figure 3. Confirmatory factor analysis of the theory of planned behavior.

Figure 4. Hybrid speed choice model based on behavioral variables.

Table 3. Estimation results of the hybrid speed choice model

Variable	Speed group		Estimate
Discrete choice part
Constant	Fast driving		−0.75 (−2.90)
	Limit driving		2.45 (3.12)
Age < 25 years old	Fast driving		0.97 (2.86)
	Slow driving		−0.46 (−2.64)
Male	Fast driving		0.86 (3.12)
	Limit driving		−0.13 (−2.19)
PBC	Slow driving		0.36 (2.84)
	Limit driving		0.98 (3.26)
ATT	Limit driving		1.38 (3.55)
	Fast driving		−0.26 (−2.70)
INT	Limit driving		1.04 (2.97)
	Fast driving		−0.12 (−23)
Latent variable part	PBC	SN	ATT	INT
Expensive car	−0.54 (−3.48)	–	–	–
Well educated	–	0.76 (4.12)	–	–
Age < 25 years old	–	–	−1.03 (−3.31)	–
Age over 60 years old	–	–	0.61 (3.75)	–
Male	–	–	–	−0.24 (−2.96)
Experienced driver	–	–	–	0.11 (2.51)
PBC	–	–	–	0.46 (3.30)
SN	–	–	–	0.27 (2.89)
ATT	–	–	–	0.86 (4.58)
Random term	0.48 (7.14)	0.83 (9.93)	0.54 (6.22)	0.18 (8.65)
Measurement relationship	Indicator	$\gamma$	$\zeta$	$\sigma$
PBC	I2-PBC	0.45 (5.23)	1.76 (9.42)	−0.37 (−12.26)
SN	I2-SN	−0.24 (−3.36)	1.52 (13.55)	−0.15 (−16.72)
	I3-SN	−0.72 (−4.12)	1.83 (10.05)	−0.41 (−14.42)
ATT	I2-ATT	0.83 (4.71)	2.14 (13.55)	0.17 (16.72)
	I3-ATT	−1.12 (−7.94)	1.85 (18.16)	−0.96 (−16.83)
	I4-ATT	−0.66 (−3.48)	1.98 (20.78)	−1.05 (−23.54)
INT	I2-INT	−0.26 (−5.88)	2.57 (15.45)	−0.63 (−12.19)
	I3-INT	−0.66 (−3.48)	2.16 (9.66)	−0.18 (−8.32)
Number of observations	1026
Initial log likelihood	−1652.01
Final log likelihood	−1127.17
Rho-square for the model	0.32

Note1. Only statistically significant variables at CI 95% are retained in the final HCM.

Note2. T-statistics are shown in parentheses.

Figure 5. Changing share on speeding groups after applying policy scenarios.

Table 4. Predicting changes in the speed choice alternatives

Scenario	Share of alternative (%)
	Slow driving	Speed limit range	Fast driving
Do Nothing*	33%	52%	15%
(a) being male	31.5%	51.5%	17%
(b) being younger than 25 years old	30%	51.5%	18.5%
(c) an enhancement in PBC	34%	55.5%	10.5%
(d) an enhancement in attitudes	32.5%	58%	9.5%
(e) an enhancement in intentions	32%	56.5%	11.5%
(f) being female plus an enhancement in PBC	30%	57.5%	12.5%
(g) being female plus an enhancement in attitudes	33.5%	58.5%	8%
(h) being female plus an enhancement in intentions	32.5%	58%	9.5%
(i) being older than 25 plus an enhancement in PBC	38%	52.5%	9.5%
(j) being older than 25 plus an enhancement in attitudes	34.5%	55.5%	10%
(k) being older than 25 plus an enhancement in intentions	37%	54%	9%

*The share of alternatives (market shares) is based on estimated HCM.