They should not be used until you are already changing lane, at which point they can be left on for another two miles. If own a 4WD or pickup you can pull out of side roads when you feel like it, and drive really close behind any other vehicle. This is despite the statistics which show that your vehicle's raised centre of gravity actually makes it more hazardous to the occupants in the case of an accident. During snow conditions you may drive as usual, pausing only to slide into the roadside to demonstrate that 4WD traction does not have any effect on stopping distance on ice. You are allowed to take your 4WD off road, but expect to be overtaken by mountain bikes doing more than 5 mph.
Cows can do what they want.
Level crossings should be crossed by walking under the barrier until it is too late.