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I don't get it. I have 'wouldn't' for these sentences. After 'where', what tense am I supposed to use?
1. He wouldn't drive fast on a raod where he didn't know how long it was.
2. He wouldn't drive fast on a raod where he doesn't know how long it is.

By the way, if #1 and #2, are correct, do they both mean the same thing?

What about these ones:
3. He wouldn't drive fast on a raod where he didn't know how long it is.
4. He wouldn't drive fast on a raod where he doesn't know how long it was.
For #3 and 4, I have mix tenses, are they wrong?

Thanks.
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I'd choose #1 as well:

1. Jack wouldn't drive fast on a road where he didn't know how long it was.

This is in effect a type 2 conditional. It means that Jack (in our opinion) is unlikely to drive fast on a road if he doesn't know how long it is. Using 'would' + past tense makes the sentence more 'remote' – which makes sense, because we clearly consider it a 'remote' possibility.

The other versions are unhappy mixtures of tenses, but are likely to occur in conversation or internet English, where we often find mixed conditionals.

MrP
Comments  
Well, I would choose #1:

He wouldn't drive fast on a road where he didn't know how long it was.

This means he didn't have the habit/didn't like to drive fast, because he didn't know how long the road was. I consider it to be in the past.

Probably someone will like some of the other sentences as well.
 MrPedantic's reply was promoted to an answer.