Utilizing the tailor welded blanks (TWB) design along with the latest AHSS grades for the front rails on a sedan was studied to reduce the weight of the vehicle and improve the crash safety performance. To find the most efficient material usage, the front rail parts were tailored into sections with separate gauges. A structural gauge optimization study for the tailored front rails was conducted by IIHS moderate overlap frontal crash with tailored section gauges as design variables. The equivalent static loads (ESL) method was adopted for the gauge optimization, which allows many design variables to be optimized simultaneously. The torsion and bending stiffness of the sedan body in prime were set as design constraints, and would not be compromised. The optimal gauge configurations of the TWB designs by ESL optimization suggest that the weight of the frontal rails can be reduced by more than 30% while still maintaining the frontal safety performance. These TWB designs were validated by US-NCAP full frontal impact and show similar performance with baseline. AK Steel’s newly launched NEXMETTM1000 grade was selected on four parts of the front rails to replace the original HSLA350 grade. The optimal tailored frontal rail design using NEXMETTM1000 grade was obtained through ESL gauge optimization and validated by US-NCAP full frontal impact. Compared with the baseline HSLA350 grade, the NEXMETTM1000 grade offers better crash safety performance with more weight reduction potential. An optimal gauge coefficient is proposed initiatively in this study to evaluate the material efficiency of the tailored blank sections and the amount of gauge changes required for each section to reach the most efficient material usage. The optimal TWB gauge configurations for HSLA350 and NEXMETTM1000 grades through ESL were evaluated using this optimal gauge coefficient. The critical locations on front rails for crash safety were identified and the amount of gauge changes needed characterized. The tailor welded blanks technology can be implemented in the front rail design to reduce weight and improve crash safety. This optimal gauge coefficient can guide the automotive design for lightweighting.