The Back Pack on Wheels.
Apparently, whoever invented this has never had to navigate pedestrian rush-hour traffic. I have tripped over more than my fair share of these contraptions. In crowded rail stations and sidewalks, no one looks down - everyone is focused and rushing straight ahead to either catch a train before it departs, jump on a bus before the door closes, or to go into the pocket. If I see a space for me to jump into while walking, I don't think to look down to see if someone is dragging a backpack.
How heavy must a backpack be for someone to have to drag it rather than just sling it over a shoulder? Most of the ones I have seen look to be practically empty. If you need to carry your work to and from in a backpack, you apparently have very poor time-management skills. It seems to be mostly older women who use these things, probably spouting off that they have back problems or simply cant lift or carry a bag. However, I am sure these same women have no difficulty carrying shopping bags during a sale at Marshall Field or a 10-pound ball on bowling night.