3 little post scripts:
1) I seem to have meant AddATex. There is ATex, too, I believe, but AddATex is what is recommended in that blog and elsewhere. Not sure how much you will note in your case, though. ATex puts white or yellow in front of the background, AddATex adds the colour to the background which in my book will sum up to pretty much the same thing. But Derek's blogs are the gold standard, so doing as he say cannot be far off.
2) I forgot to mention point lights. I believe that they would be a waste in your case, unless the driver stops next the entrance and the player spends some time looking at it. But a lot depends on the performance of your rig, and the number of other lights in the scene.
3) I assumed you have separate day and night textures. During the day, the situation will be different. You will create a triangle of light from the top corner diagonally along the wall down to the bottom at and angle a bit steeper than 45° (I guess) and back along the bottom of the wall to the front edge. This represents the sunlight hitting the inside wall. The diagonal edge of the triangle will be fuzzy of course, increasingly so as you approach the bottom.
You either superimpose this triangle of white (with a slight blueish tint for perfection) over the darkened inside wall, using a transparency of maybe 20% (subject to experimentation). Or - maybe even better, only darken the other part of the wall.
The night texture would be what I described.