Since they aren't releasing this information, I will predict that the killer is coming from Northern Virginia, through I-95, and tooling through Maryland looking for his victims. The killer is probably a white male, in his late 20's-30's.
Do you have access to the software or is it a hunch?
I agree. All it really takes is an eye for likely spots, that are visible from the freeway. This explains the apparent randomness. And antivenom has provided a reasonable assesment of what a "likely spot" looks like.
The guy could case the area in about 10 minutes. And his getaway is simple if he can simply rejoin traffic.