Around here if you happen to be near a snow plow when it’s dark it’s common to see a light shower of sparks flashing from the plow blade as the big plows barrel down the trans Canada highway. The blades often do scrape right down to the asphault and remove any little snags… the blades get worn down scraping over the millions of little stones in the pavement (hence the sparks). I have a fence made from bolted together old plow blades; they get worn down after a while from all the little protrusions that they chop off and hard surfaces they scrape against.
So the answer is the mass of a driven snow plow simply sheers off some small snags, and the relative dullness of the blade and/or the springs will let it skip over others while your comparatively tiney, light, sharp hand shovel with a very small amount of force pushing it catches and gets hung up on evey little chunk of sod and sidewalk crack.
Apparently, even with the folding sections you can hear and feel when you hit something. I was listening to an NPR report on snow plow drivers, in Boston I believe. He said that they try to remember where the big snags are so they don’t catch them. Then you heard the big metal bang when he hit one.
One thing the plow blades get caught on is the reflective line markers on the highway. Driving along I-95 right now is fairly scary in places (especially in rainy/snowy conditions) because no one knows where their properly lane is. So there’s even more swerving than usual.
Recessed markers exist. Google “snowplowable road marker” and you’ll see some patent filings and passing mentions in other material about road reflectors.
I think one issue is that in a snowfall, the recesses fill with snowpack and defeat the purpose of having a marker, in a time when you need a road marker the most (when normal street markings are obscured with snow).
In other words, they solve one problem at the expense of no longer being able to solve the main problem when it’s needed most. Which probably explains why I’ve only seen a few cities use them.
I clean my sidewalks and the Church walks with this kind. The spring steel part will not prevent it from getting caught in cracks because that is the job of the one doing the shoveling.
So weather it is plowing with my Boss plow on the pickup or using the hand operated plow shovel the technique is to angle across the cracks. The angle that throws the snow off the road also keeps the plow operator from damaging there equipment and themselves.
At the church there are 2 snow shovels by the front door. The spring steel one is never used until I get there and I suspect it is because of the cracks/joints that are hit head on. :dubious::smack: