Cameras with true WDR use multiple exposures, typically including one that is relatively short. During the day, this is typically not a problem, as there is a lot of light. However, at night, this frequently results in worse low light performance (and with some manufacturers blurring). This is why many manufacturers automatically turn off WDR at night.
At the very least, you are going to want to turn WDR offf at night.
Probably the biggest variable is how wide a FoV do you want to cover. You should be fine using a 5 - 100mm lens for an object 30 meters away, but is the FoV narrow (i.e., just one lane) or wide (4 lanes and the adjacent building, etc.).