Why do rail tracks have an '$I$-shaped' girder?

(N/A) Rail tracks are designed with an '$I$-shaped' cross-section to provide maximum structural strength and rigidity with minimum material usage.
By concentrating the material at the top and bottom flanges,the moment of inertia is significantly increased,which minimizes bending or buckling under the heavy load of trains.
The central vertical web provides the necessary depth to resist shear forces while keeping the track lightweight and cost-effective.