There are many things which affect travel conditions. The weather and traffic are the major contributors. There are of course other things which can affect the condition such as highway construction, as well mandatory military use of interstate highways.
Other fortuitous events such as those affecting the national security as well as earthquakes and other natural disasters affect travel conditions.
Major contributing factors to the capricious travel conditions are weather and traffic. Both of which sometimes come rather unannounced and surprising the motorists. While the weather can be predicted and to a certain degree, be advised to people, there are of course certain exceptions where the weather can bring about fortuitous events to affect the travel conditions. Weather like snow, heavy rains, and even heatwaves can affect the travel conditions. Heavy rains and snow can cause roads to be slippery and therefore more dangerous. Heatwaves also affect the travel condition as when it is too hot, car motors can overheat. It is then to be expected to drive with more caution when faced with these weather conditions.
Traffic is also a major contributor in travel conditions. While interstates and highways do not generally suffer from traffic, accidents and other events can cause travel conditions which can impede efficient highway travel. Car accidents are a leading factor affecting traffic. The best step to avoid this is to be briefed about accidents in the interstate or in the highways. Or if you encounter an accident, report it immediately to the corresponding agencies.