Waveguide crossings employing tilted MMI structures on silicon wire waveguide are proposed and demonstrated. Intersecting angle of the two MMI waveguides is optimized for low crosstalk. The optimization is carried out with input polarizations specified. On the fabricated MMI crossings, crosstalk lower than -38 dB in the C-band was experimentally confirmed. A novel polarization-insensitive crossing based on a diversity circuit was fabricated. Crosstalk lower than -30 dB in the C-band is demonstrated.