If there hadn't been so much traffic on the road, I ................... (not/be) so late.

[angelene001]

A: Why are you so late?
B: If there hadn't been so much traffic on the road, I ................... (not/be) so late.

I would use mixed conditional here:
There was a lot of traffic -> we need the third conditional to talk about the hypothetical past
I am late -> we need the second conditional to talk about the hypothetical present situation

If there hadn't been [but there was] so much traffic on the road, I wouldn't be [ but I am] so late.

However, the key says:
If there hadn't been so much traffic on the road, I wouldn't have been so late.

But person A says: Why are you so late?
So how can we use the third conditional here which is for past situations?

 

[tunaafi]

We interpret 'wouldn't have been' as 'wouldn't have arrived'.

 

[angelene001]

Thank you.
So this example would be much clearer with "arrive" instead of "be".

Can "be late" mean both:
a) the state of not being on time
b) the action of not arriving on time

 

[Uncle Jack]

Can "be late" mean both:
a) the state of not being on time
b) the action of not arriving on time

Yes, in general terms, but they aren't really interchangeable. If speaker B has only just arrived, then speaker A would be unlikely to use the (b) form, whereas speaker B can only really refer to the action in a conditional sentence.

This is, of course, purely a language exercise. I cannot really imagine anyone actually using a third conditional in this situation, unless they were passing the blame back to the original speaker: "If you hadn't told me to go through the centre of town to get here, I wouldn't have been late".