Speedly or fastly

[Turkish is the best]

You can't drive to Istanbul speedly because there are a lot of rough roads.

You can't drive to Istanbul fastly because there are a lot of rough roads.

How can I the sentence to become meaningful?

 

[Tdol]

They don't work. How about this:

You can't drive to Istanbul fast/quickly because a lot of the roads are rough.

 

[emsr2d2]

Neither "speedly" nor "fastly" is an English word. "Speedi​ly" exists.

 

[tzfujimino]

Well, "fastly" seems to exist in some dictionaries here:
http://www.onelook.com/?w=Fastly&ls=a

I wouldn't use it, though.

 

[emsr2d2]

You can't drive to Istanbul speedly because there are a lot of rough roads.

You can't drive to Istanbul fastly because there are a lot of rough roads.

How can I the sentence to become meaningful?

Note my changes to your post above. I'm sure in a previous thread, I gave you the rules of written English. They included starting every sentence with a capital letter, capitalising the word "I" every time you write it, capitalising proper nouns and ending every sentence with a single, appropriate punctuation mark. You did not follow any of those rules in this post.

 

[Turkish is the best]

Dear emsr2d2 and Piscean;

I noted your changes to my post. Thanks for your understanding.

 

[Tdol]

Well, "fastly" seems to exist in some dictionaries here:
http://www.onelook.com/?w=Fastly&ls=a

I wouldn't use it, though.

I think it is different- it is from fast meaning secure, and we don't it is as an adverb for fast (= quick). And I am not sure that we still use it for that- it may be archaic.