I have modified damping and grip on grass and sand so it is a bit more realistic.
You can also copypaste everything below to your surfaces.ini file:
[SURFACE_0]
KEY=ROAD
FRICTION=1
DAMPING=0
WAV=
WAV_PITCH=extended-0
FF_EFFECT=NULL
DIRT_ADDITIVE=0
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=0
VIBRATION_GAIN=0
VIBRATION_LENGTH=0
[SURFACE_1]
KEY=PIT
FRICTION=1
DAMPING=0
WAV=
WAV_PITCH=extended-0
FF_EFFECT=NULL
DIRT_ADDITIVE=0
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=1
VIBRATION_GAIN=0
VIBRATION_LENGTH=0
[SURFACE_2]
KEY=GRASS
FRICTION=0.6
DAMPING=0.05
WAV=
WAV_PITCH=extended-0
FF_EFFECT=1
DIRT_ADDITIVE=1
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=0
VIBRATION_GAIN=0.5
VIBRATION_LENGTH=0.5
[SURFACE_3]
KEY=GRAVEL
FRICTION=0.6
DAMPING=0.05
WAV=
WAV_PITCH=extended-0
FF_EFFECT=1
DIRT_ADDITIVE=1
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=0
VIBRATION_GAIN=0.5
VIBRATION_LENGTH=0.5
[SURFACE_4]
KEY=SAND
FRICTION=0.5
DAMPING=0.3
WAV=
WAV_PITCH=extended-0
FF_EFFECT=1
DIRT_ADDITIVE=1
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=0
VIBRATION_GAIN=0
VIBRATION_LENGTH=0
[_SCRIPTING_PHYSICS]
ALLOW_TRACK_SCRIPTS=1
ALLOW_DISPLAY_SCRIPTS=1
ALLOW_NEW_MODE_SCRIPTS=1
ALLOW_TOOLS=1
Managed to fix/rework lanes I messed up before, added more AI lines. Whole map is covered by lanes now.
You can also replace your surfaces.ini file with this:
[SURFACE_0]
KEY=ROAD
FRICTION=1
DAMPING=0
WAV=
WAV_PITCH=extended-0
FF_EFFECT=NULL
DIRT_ADDITIVE=0
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=0
VIBRATION_GAIN=0
VIBRATION_LENGTH=0
[SURFACE_1]
KEY=PIT
FRICTION=1
DAMPING=0
WAV=
WAV_PITCH=extended-0
FF_EFFECT=NULL
DIRT_ADDITIVE=0
IS_VALID_TRACK=1
BLACK_FLAG_TIME=0
SIN_HEIGHT=0
SIN_LENGTH=0
IS_PITLANE=1
VIBRATION_GAIN=0
VIBRATION_LENGTH=0
[_SCRIPTING_PHYSICS]
ALLOW_TRACK_SCRIPTS=1
ALLOW_DISPLAY_SCRIPTS=1
ALLOW_NEW_MODE_SCRIPTS=1
ALLOW_TOOLS=1
Road network is done, AI is present everywhere where I wanted it to be. Only thing to do is to add second, parallel lane in some areas.
Connected Rockport to Rosewood. At least one line on highway and main road.
Rosewood complete - at least one AI lane each direction. Started having little performance issues due to highway lanes presence. If you have performance issues, you can always delete highways, I don't know any other solution right now.