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155 B Model of Attitudes Towards Speed Limit Level As mentioned in Section 4.2.1, the 2000 Motor Vehicle Occupant Safety Survey (MVOSS) asked respondents if they thought that current speed limits were too low, about right, or too high. 76.6% of the respondents were satisfied with current speed limits, 16.2 % felt they were too low, and 7.2% thought they were too high. In comparison, Haglund and Aberg (2000) reported corresponding attitudes at 61.1%, 37.0%, and 1.9% by Swedish drivers on highways with a 90 kph (56 mi/h) speed limit. Of course, U.S. freeway speeds are often above 100 km/h, so Americans could be expected to be less likely to want higher limits than their Swedish counterparts. In order to explore more deeply the determinants of driversâ attitudes towards speed limit levels, an ordered probit model of opinion about speed limits as a function of driver characteristics was developed. Data available from the MVOSS are described in Table 4-1, and the model coefficient estimates are presented in Table B-1. Table B-1 reveals that male, employed, married, and higher-income drivers favor higher speed limits, in contrast to drivers of vans, SUVs, and pickup trucks. People who favor seat belt laws and those who experienced crashes (as drivers) in the past support lowering speed limits, while those who frequently pass others, recently experienced being stopped by a police officer, drink more often, and/or indicated a higher highway driving speed tend to favor speed limit increases. Table B-1 â Results of Ordered Probit Model of Speed Limit Opinion Initial Model Final Model Variables Coeff. Std.Err. P-value Coeff. Std.Err. P-value Constant 0.7972 0.1865 0.0000 1.2464 0.1826 0.0000 Indicator for Male -0.0327 0.0327 0.3174 -0.1959 0.0323 0.0000 Age 9.770E-03 5.308E-03 0.0657 0.0338 5.484E-03 0.0000 Age Squared -7.620E-05 5.316E-05 0.1518 -2.022E-04 5.653E-05 0.0003 Hispanic 0.0197 0.0505 0.6965 Married 4.838E-03 0.0365 0.8945 -0.0743 0.0385 0.0538 College Educated 1.988E-04 0.0291 0.9946 Employed -0.0215 0.0323 0.5054 -0.1124 0.0340 0.0010 Income 8.784E-07 1.707E-06 0.6068 -1.635E-06 4.488E-07 0.0003 Income Squared -8.707E-12 1.133E-11 0.4423 Indicator for Central City 4.358E-04 0.0355 0.9902 Indicator for Van 0.0537 0.0458 0.2407 0.2785 0.0470 0.0000 Indicator for Pickup 0.0393 0.0441 0.3726 0.0962 0.0421 0.0225 Indicator for SUV 0.0583 0.0485 0.2296 0.1920 0.0488 0.0001 Indicator for Heavy Truck -0.0644 0.0978 0.5101 Indicator for Other Vehicle -0.1071 0.2413 0.6573 -0.5126 0.2027 0.0114 Driving Frequency 3.074E-03 0.0300 0.9184 Seatbelt Frequency -0.0282 0.0212 0.1826 -0.0952 0.0206 0.0000 Seatbelt Law Support 0.0470 0.0196 0.0166 0.1291 0.0195 0.0000 Opinion of Other Drivers 0.0103 0.0164 0.5284 Pressure to Exceed Speed Limit -3.407E-03 0.0156 0.8276 0.0640 0.0158 0.0001 More Pass 0.0928 0.0428 0.0303 0.4841 0.0411 0.0000 Neither Pass 0.0923 0.1088 0.3963 0.2683 0.1023 0.0087 Pass Same 0.0715 0.0975 0.4634 0.1686 0.0940 0.0729
156 Speed on Highway -3.861E-03 2.022E-03 0.0562 -0.0166 1.980E-03 0.0000 Stopped by Police -0.0205 0.0573 0.7208 -0.0915 0.0395 0.0205 Recent Traffic Ticket -0.0139 0.0716 0.8460 Drinking Days -2.249E-03 2.389E-03 0.3465 -7.867E-03 0.0021 0.0002 Number of Drinks 1.502E-04 9.553E-03 0.9875 Drinking and Driving Days -1.431E-03 7.327E-03 0.8452 Injured in Crash -0.0754 0.0816 0.3553 -0.3216 0.0670 0.0000 Injured as Driver 0.0396 0.0764 0.6044 0.1832 0.0703 0.0092 Number of Injury Events -6.926E-04 0.0286 0.9807 0Ï N/A N/A 1Ï 2.4496 0.0398 0.0000 2.7755 0.0418 0.0000 Nobs. 4,136 4,136 Loglik constants only -2845.62 -2845.62 Loglik -2512.33 -2514.73 LRI 0.1171 0.1163 Adj. LRI 0.1055 0.1086 Note: Y = 0 (current speed limits are too low), 1 (limits are about right) and 2 (limits are too high). Figure B-1 illustrates some predicted responses to this question for different respondent characteristics. Older persons are predicted to respond that the current speed limits are too high; however, this trend is maximized at an age of about 80 years. The gender effect is much bigger than the vehicle-type effect: females are more likely to consider the current speed limits to be too high, regardless of the vehicle types that they use. Van drivers are estimated to be the most likely to favor lowering limits, followed by SUV drivers; pickup and passenger car drivers are the least likely to support lowering speed limits. Figure B-1 â Probability of Responding that the Current Speed Limit Is Too High Note: Reference individual is married and employed, and exhibits average values of all other explanatory variables included in the final model shown in Table B-1. 0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 10 20 30 40 50 60 70 80 90 100 Age (years) P ro b( C ur re nt S pe ed L im it is T oo H ig h) female (VAN) female (SUV) female (PU) female (PC) male (VAN) male (SUV) male (PU) male (PC)
