Ice can happen on bridges and anywhere else.
Wind strength and direction can effect freezing on one and not another bridge even on same road.
Sun/shade on a road often matters too. Sun melts most areas then hit a shade stretch that's still frozen is a big problem w/ some roads. Thunk was I76 near Philly had a big wreck last year because of this.
Some areas may have plain salt but others areas use calcium chloride etc. that have different temps they work or not. So even walking in low temps can be "fun."
And just because they "salt" the roads and so on "today," overnight or next day can still freeze again on spots to whole road depending on temp and other things.
Worse if you "speed for conditions" or even turn a little at low speed can spin you out on ice. Real "snow tires," even w/ studded snows, may not help when you hit ice.
I don't drive in freezing weather as much as possible. Oh I can drive in most any type of crap like many people grew up in Northern States but not here because most others wreck just for rain because simply won't slow down and tailgate.
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
The Ogre's Fiero Cave