True. But if he's headed north to the boonies, he's likely staying on Central Expwy as he passes through Plano (no lights red or green, on that hwy).
From WM's home it's 29 miles to Melissa, about 34 miles to Anna. That time of night a driver could reach Melissa via Central in abt 25 min or less (not speeding), and Anna, about 5 minutes later. But that's as far as he could go, time-wise, and leaving little to no time left for hiding her body.
Here's the rough lineup of cities along Central, listing north to south:
Anna
Melissa
McKinney
Allen
Plano
Richardson
Dallas
(ETA: I'm not getting the strong sense he went that far, personally--just seems like there's not enough time)
What about lakes and rivers?