According to Capital Metro:
Who will have priority at traffic lights?
A level of priority is typically provided for light rail to help the service run efficiently. This occurs as a part of planning that helps the light sequencing to support the major traffic flow (such as the inbound traffic in the morning peak). This means that the major vehicle traffic flows generally benefit through light rail priority work.
We already know that the railway will go on the same grade (i.e. level) as cars, trucks, buses, bicycles and people. This means we will fight over who has priority at intersections. Unless the trams can have absolute priority, they will be time-inefficient.
Elevating the public transport overcomes these issues quickly.
Is there evidence that the government has considered the option to elevate the trams or use another elevated technology, like aerial ropeways (gondolas)?
Lastly, must we use steel wheels? Paris metro moved to rubber wheels.