Duplicate the layer and desaturate. Use the channels and select all of just the red layer and hit control C.
select all the channels so as everything is visable again.
Go back to layers, make a new layer and hit ctrl v.
Set the layer type to exclusion.
hit ctrl i to inver the colour.
Select everything and copy it and then paste it to a new layer.
Set the layer type to colour
Hide the two layers below it
You should have all the red showing up on a mostly black and white background.
Then you can copy the original to another layer, desaturate it and delete any bit you want so as the red car shows through without having to worry about how accurately you do it. This should work because the picture was mainly red or green, so easy to extract without masking. if you had another picture with lots of different colours it would not work so well, or if the picture was a different colour you may have to chose a different channel.
There are loads of other ways to do it but this should get you started without having to mess around with masks.