one thing to really watch out for are those unplowed slush piles on the highway, that collect between lanes (usually around 4-6 inches high). When travelling at city speeds, hitting one of these is no problem.

but hitting one of these with one of the front tires at highway speeds can make your car spin, with all the related consequences (e.g., you can careen out of control across the median into oncoming traffic). The reason this is dangerous is that slush is quite dense, and offers a lot of resistance to your tire at highway speeds. Hitting one of these piles at highway speeds imparts a torque on your vehicle, and with the reduced traction on your other tires, will make your vehicle spin.

the heavier your vehicle, the less susceptible it will be to this reaction, but one has to be aware that vehicle speed is another factor that contributes to this.