Keep a very careful eye on the overhead directional signs. If the lane in which you are driving has a yellow background then you are in a This lane must exit lane. Be aware of this situation because you must either change lane quickly or leave the freeway at the next exit - your lane will leave the freeway. Lane discipline is practically non-existent. It is essential, therefore, to watch both left and right mirrors to see who is overtaking, and from which side.
Speed limits vary tremendously.
The signs are black lettering on a white background. This would be, typically, 35mph for the lower limit and 45 mph for the upper. Whilst considering school speed limits it is appropriate to mention school buses. A common sign is that which reads Reduced speed ahead . A colleague informs me that Montana have a daytime speed limit which is prudent and safe .