Crash Frequency Minimization with Severity Mitigation in Road Geometric Design Using Chance Constraint Programming Optimization

Table 9

Results of linear regression models for travel speed during 1–3 pm

Model summary for 25CBD
Dependent variable	Number of observations	Adjusted R square	Standard error
Vehicles’ travel speed	1456	0.177	5.440
Coefficient estimate
Independent variable	Coefficient	t-statistic	Variable notation
Constant	23.651	41.539
Indicator of 9 ft lane width	−6.186	−14.445
Indicator of 10 ft lane width	−4.236	−8.654
Model summary for 35NCBD
Dependent variable	Number of observations	Adjusted R square	Standard error
Vehicles’ travel speed	3099	0.055	5.200
Coefficient estimate
Independent variable	Coefficient	t-statistic	Variable notation
Constant	36.972	31.009
Indicator of 9 ft lane width	3.213	3.795
Indicator of shoulder appearance	2.503	7.390
Number of through lanes	−0.832	−2.165
Number of vehicles in every five minutes	−0.024	−3.998
Model summary for 40 MPH
Dependent variable	Number of observations	Adjusted R square	Standard error
Vehicles’ travel speed	5005	0.379	4.992
Coefficient estimate
Independent variable	Coefficient	t-statistic	Variable notation
Constant	42.885	113.809
Indicator of 10 ft lane width	−6.279	−24.451
Indicator of 11 ft lane width	1.209	5.339
Number of vehicles in every five minutes	−0.029	−5.129
Model summary for 45 MPH
Dependent variable	Number of observations	Adjusted R square	Standard error
Vehicles’ travel speed	4415	0.448	5.326
Coefficient estimate
Independent variable	Coefficient	t-statistic	Variable notation
Constant	34.885	64.940
Indicator of 10 ft lane width	−3.587	−18.952
Indicator of 11 ft lane width	9.901	28.769
Number of vehicles every five minutes	0.029	5.934