  The metal-insulator transition and unconventional metallic transport in
vanadium dioxide (VO$_2$) are investigated with a combination of spectroscopic
ellipsometry and reflectance measurements. The data indicates that electronic
correlations, not electron-phonon interactions, govern charge dynamics in the
metallic state of VO$_2$. This study focuses on the frequency and temperature
dependence of the conductivity in the regime of extremely short mean free path
violating the Ioffe-Regel-Mott limit of metallic transport. The standard
quasiparticle picture of charge conduction is found to be untenable in metallic
VO$_2$.
