Roads are most certainly impassible, even many driveways.
Cars are not a safe place to be and some people have become trapped and drowned.
My mom's house had water come very close to the house but it retreated when the rain paused. Same story for most people I know. A few are dealing with water inside their houses.
A coworker of my mom had 5ft of water at their house and two of their ponies drowned.
---------- Post added at 03:20 PM ---------- Previous post was at 02:49 PM ----------
As far as evacuation, Houston is seeing rain but not wind (other than tornadoes).
No one in Houston is likely to be killed by flying debris or collapsing houses. But people are dying by trying to leave in cars and drowning.
---------- Post added at 03:25 PM ---------- Previous post was at 03:20 PM ----------
Nursing home seniors in waist deep water in Dickinson. They have been confirmed rescued. (Editted)
Unsurprisingly, both Houston airports have cancelled all flights.