The Varia knows the approach speed. Actually, that is how it works, it measures closing speed, not just senses objects and Only things with a certain closing speed or above relative to you and your bike trigger warnings. (Thus no alarms when riding in a group)
For approach speed there is a dot on the right side of your head unit representing vehicles ( and it will show multiple). The dot(s) move from bottom to to top as the vehicle approaches and the faster it’s closing on you the faster the dot moves. After seeing just a few it’s pretty easy to judge.
I do most of my riding on roads where the cars are going 45 or under. The radar picks up vehicles well before you hear them. I use the time to decide where I want to be. If the far right or shoulder rideable I move right. If the shoulder is narrow and or I’d have to ride through potholes, covered with debris etc, I move left and make the car see me and give me space (within reason of course).
For me though the biggest benefit in knowing there is no vehicle approaching… Many of 5he roads I ride on suck and the radar allows me to pick my line and ride anywhere in the whole lane I want to but still gives me plenty of time to get over when a car is coming. Seriously, the knowing no car is back there is just as awesome as getting a warning when one is back.
After 30 years of riding I got a Varia last year and quickly decided I’ll never do another ride without it.