Iowa’s string of winter storms is putting state snowplow drivers and state troopers trying to keep roads passable and assist motorists at risk of crashes this winter.So far this season, 50 state plows have been struck by drivers, according to the Iowa Department of Transportation — most over the last seven weeks when more trucks were in service due to incessant winter weather conditions.“It’s been a really rough winter for our snow plows,” said Craig Bargfrede, the Iowa DOT’s winter operations administrator.