What you see is normal I think. I've seen the red dashed line before.
When there's a traffic problem, you'll also see the cars on the right hand side of the screen become yellow or red. Touching the cars will display a screen with details about the traffic delay that lies ahead.
If you only have a 1 min delay, you're not likely to notice any difference in your arrival time but, if there's a significant delay, the arrival time will change until the traffic delay disappears.
A few weeks ago I had a 25min traffic warning for the road I was actually on and there was no traffic around at all!