I did struggle a bit on this. The posted image was as far as I could go without also blowing the red channel.
After posting here, the whites did appear more grey than I thought they had been - perhaps due to white page background? [shrug]
I replaced the image with one that locally brightened the whites in the sign and the speed bump.
I think it's an improvement (I know you can't compare now). I wouldn't go any further though.