If you leave the house at about the same time every work day, traffic speed or volume won't change much. Get to know the areas where motorists perform their most risky driving. If you ride only during day light, your route may always be the same. However, during low light conditions, you may wish to find a route that has better sight lines for you and motorists. Front and rear lights, required by law, and a good dose of reflective material, can make your ride a pleasant and safe one.
Road conditions change with the weather and road maintenance schedules.
Puddles of rain can hide rough roads. When the rain goes away, slippery sand can remain in corners. Be careful around road maintenance projects too, there are often multiple levels of pavement which can redirect your front wheel. You have to admit, during heavy rain it is tough to see out of a car window. Consider driver visibility when you are planning your rainy day route.