Doctor Who: 12 Cool Details Russell T Davies Just Revealed About New Earth & Gridlock
3. The Car Windows Were Smeared Because The Team Couldn't Afford Any CGI Work
Yet another story about Doctor Who and budget limitations. Shocking, we know.
Since a good chunk of Gridlock takes place inside a couple of futuristic cars, Davies and his team had many conversations about how to implement the car windows. In order to do them properly (as in, showing the other cars and the rest of the Undercity outside each window), every single shot that featured a window would've had to be put through the VFX machine, but financially, this simply wasn't viable.
And so, a sneaky, quite inventive solution was devised: the windows were smeared with dirt and grime instead.
Brilliantly, this doesn't just work as a cost-saving measure - it also works within the context of the episode. These cars are all travelling through the Undercity where the air is dirty, and it's not like there are car washes for people to use. It just makes sense that everybody's windows would be covered in a thick layer of filth.