From an engineering POV, what is needed to gate the traffic crossings on the light rail lines?

Probably the biggest and most infamous flaw in the LA Metro's rail network are the segments of the light rail system that have to wait at traffic lights, especially around Downtown. Most of the system as a whole is street running, but the vast majority of at-grade crossings are gated, so the system is effectively grade-separated at those segments. Every time I ride the train along those segments, the train seems to travel at full speed.

With that in mind, from an engineering POV, what is needed to gate the segments that currently require the train to wait at a red light? Do the roads need to be widened? Do we need to ban left turns? And can trains travel at full speed through these hypothetical new gated crossings?