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"High-velocity features" (HVFs) are spectral features in Type Ia supernovae(SNe Ia) that have minima indicating significantly higher (by greater thanabout 6000 km/s) velocities than typical "photospheric-velocity features"(PVFs). The PVFs are absorption features with minima indicating typicalphotospheric (i.e., bulk ejecta) velocities (usually ~9000-15,000 km/s nearB-band maximum brightness). In this work we undertake the most in-depth studyof HVFs ever performed. The dataset used herein consists of 445 low-resolutionoptical and near-infrared (NIR) spectra (at epochs up to 5 d past maximumbrightness) of 210 low-redshift SNe Ia that follow the "Phillips relation." Aseries of Gaussian functions is fit to the data in order to characterisepossible HVFs of Ca II H&K, Si II {\lambda}6355, and the Ca II NIR triplet. Thetemporal evolution of the velocities and strengths of the PVFs and HVFs ofthese three spectral features is investigated, as are possible correlationswith other SN Ia observables. We find that while HVFs of Ca II are regularlyobserved (except in underluminous SNe Ia, where they are never found), HVFs ofSi II {\lambda}6355 are significantly rarer, and they tend to exist at theearliest epochs and mostly in objects with large photospheric velocities. It isalso shown that stronger HVFs of Si II {\lambda}6355 are found in objects thatlack C II absorption at early times and that have red ultraviolet/opticalcolours near maximum brightness. These results lead to a self-consistentconnection between the presence and strength of HVFs of Si II {\lambda}6355 andmany other mutually correlated SN~Ia observables, including photosphericvelocity.

High-Velocity Features of Calcium and Silicon in the Spectra of Type Ia Supernovae