Glad a few posters found the picture funny. I had a little fun making it.
Re: the differences between streetcars and light rail.
The differences are a bit bigger than just signal priority, there's also capacity, speed, and frequency of stops.
I'm sure there's more but that's what immediately comes to mind:
Signal priority
Typically streetcars work with the current turning and passing lanes, sometimes with signal priority.
In addition to signal priority, light rail has an active barrier from the street and an exclusive lane. Cars have to flow around them, it's not a shared right-of-way.
Frequency/design of stops
Streetcars stop much more often than light rail and are designed for lighter corridors. For streetcars, speed isn't a priority, like it is with light rail. Streetcars function like buses - light rail goes between hubs. Light rail generally has dedicated platforms, not just posts with signs.
Capacity
Streetcars are single vehicles, while light rail operates with multiple cars linked together, significantly increasing capacity. The individual cars also usually hold more people than a streetcar. The difference in design affects speed as well.
Vehicle design and speed
The vehicle design is different, and top speed is higher for light rail than streetcars: along with less frequent stops, higher capacity, and a much better priority system, light rail is a far faster system
There's more differences, but that's a start. And for drivers that's a good thing, because a fast, efficient system like light rail will get lots of other cars off the street and enable you to zoom down King just fine
One line of light rail has about 8x the capacity of a line of freeway traffic in peak hours, so a well-used light rail system will actually help traffic quite a bit.