Inasmuch as it has proved impossible in the case of employees of common carriers by railroad, engaged in maintenance and operation of railways doing interstate, foreign, and intrastate commerce, and in maintenance and construction of their equipment, to separate and distinguish the connection of such employees with interstate or foreign commerce from their connection with intrastate commerce, and such employees have, in fact, received no compensation under this title, the provisions of this title shall not apply to work performed by such employees in the maintenance and operation of such railroads or performed in the maintenance or construction of their equipment, or to the employees of such common carriers by railroad engaged therein, but nothing herein shall be construed as excluding from the operation of this title railroad construction work, or the employees engaged thereon: PROVIDED, That common carriers by railroad engaged in such interstate or foreign commerce and in intrastate commerce shall, in all cases where liability does not exist under the laws of the United States, be liable in damages to any person suffering injury while employed by such carrier, or in case of the death of such employee, to the surviving spouse and child, or children, and if no surviving spouse or child or children, then to the parents, minor sisters, or minor brothers, residents of the United States at the time of such death, and who were dependent upon such deceased for support, to the same extent and subject to the same limitations as the liability now existing, or hereafter created, by the laws of the United States governing recoveries by railroad employees injured while engaged in interstate commerce: PROVIDED FURTHER, That if any interstate common carrier by railroad shall also be engaged in one or more intrastate enterprises or industries (including street railways and power plants) other than its railroad, the foregoing provisions of this section shall not exclude from the operation of the other sections of this title or bring under the foregoing proviso of this section any work of such other enterprise or industry, the payroll of which may be clearly separable and distinguishable from the payroll of the maintenance or operation of such railroad, or of the maintenance or construction of its equipment: PROVIDED FURTHER, That nothing in this section shall be construed as relieving an independent contractor engaged through or by his or her employees in performing work for a common carrier by railroad, from the duty of complying with the terms of this title, nor as depriving any employee of such independent contractor of the benefits of this title.