Electric Power Infrastructure Improvement Act This bill allows a tax credit for investment in a qualifying electric power transmission line property. The bill defines qualifying electric power transmission line property as (1) any overhead, submarine, or underground transmission facility that is capable of transmitting electricity at a voltage of not less than 345 kilovolts, has a transmission capacity of not less than 1,000 megawatts, is an alternating current or direct transmission line, and delivers power produced in either a rural area or offshore; and (2) conductors or cables, or other specified equipment, necessary for the proper operation of the facility.