It is the duty of any railroad company operating within the corporate limits of the city to construct at its own cost and expense safe, suitable and convenient crossings where its tracks intersect any public street or thoroughfare in the city, upon being notified in writing by the city council so to do. The notice shall prescribe the time within which such crossing shall be constructed, and the time shall be as the city council may consider reasonable, equitable and just. In cases of unavoidable delay and after satisfactory proof thereof by the railroad company, the city council may extend the time for making such improvements for such a period as may to the council be reasonable and just. (Prior code § 21-18)