They’re built into the truck and my understanding of their purpose is to give the driver a visual of that area as it’s right under their passenger mirror
When I had to move a rig around a yard I’d use it to help judge distance to a nearby wall, for example
You are aware this isn’t a standard window that would be used for anything? The truck driver can kill pedestrians very much without that, thank you, sir and goodbye!
Edit: welp, you learn something new every day. Turns out the dog is helping kill pedestrians after all!
In the UK and EU, windows in similar positions are mandated on construction trucks to give the driver a view of other road users when manoeuvring in urban environments. They were brought in after pedestrians and cyclists were killed by having been in trucks’ blind spots.
Also, just because we can see the dog through the window doesn’t mean the dog is obstructing it entirely. The driver would be looking down at that window from above, and at an angle. Entirely likely there’s more than enough space to see through the gap between dog and window.
