When, upon an application or petition brought under the provisions of section 3783 of this title, the Board finds that a public highway crosses or is crossed by the tracks of more than one railroad and the tracks of such railroads are so near together that public convenience requires the work of separating the grades to be done under and in compliance with one order, it shall give notice to all the corporations operating such railroads to appear before it and be heard upon the application. After such notice and hearing, the Board shall determine what alterations shall be made, if any, so as to separate the grades of all such crossings at the same time, and shall determine by whom such work shall be done, and shall apportion the expense to be borne by the railroad corporations between such corporations in such manner as the Board deems just and proper. (Amended 1959, No. 329 (Adj. Sess.), § 39(b), eff. March 1, 1961.)