Eğer asfalttaki çatlak tamir edilmezse, şeritler karışabilir.

Eğer means “if” and introduces a conditional clause. In Turkish it’s actually optional: the conditional suffix -se on the verb already signals “if.” You could therefore say
Asfalttaki çatlak tamir edilmezse, şeritler karışabilir.
without Eğer, and the meaning stays the same.

asfalttaki breaks down as:
• asfalt (asphalt)
• -ta (locative case, “in/on/at”) → gives asfaltta (“in the asphalt”)
• -ki (relative suffix, “that is…”) → gives asfalttaki (“the one in the asphalt”)
So asfalttaki çatlak means “the crack in the asphalt.” The doubled “tt” comes from consonant assimilation: asfalt + -ta → asfaltta.

Using the passive edilmek (“to be done”) focuses on the action (repair) rather than the person doing it. Tamir edilmezse means “if it is not repaired.”
You can make it active by saying:
Eğer asfalttaki çatlağı tamir etmezlerse, şeritler karışabilir.
Here tamir etmezlerse is “if they don’t repair,” and çatlağı takes an accusative ending to show it’s the direct object.

Sure:
• tamir – noun “repair”
• edil- – passive verb root (from etmek, “to do”)
• -me – negation (“not”)
• -z – aorist tense marker (negative aorist is -mez)
• -se – conditional suffix (“if”)
All together, tamir edil-me-z-se = “if it is not repaired.”

When a conditional clause comes first in Turkish, it’s conventional to put a comma before the main clause for clarity:
Eğer …, şeritler karışabilir.
In informal writing or speech you might drop the comma, but in formal writing it’s recommended.

şerit = “lane” or “stripe”; şeritler = “lanes.”
Turkish verbs don’t change form for plural subjects. Şeritler karışabilir already covers “the lanes can/might get mixed.” You could add a personal suffix and say şeritler karışabilirler, but it’s more common to leave it off.

Root verb karışmak = “to mix” or “to get mixed up.” Add the ability/possibility suffix -abil/ -ebil, then the aorist -ir:
karış- + ​abil- + ​ir → karışabilir
So karışabilir means “it can/might get mixed up.” The mood here expresses potential rather than a definite outcome.

Yes. Instead of the formal passive tamir edilmek, you can use the verb tamir yapmak (to repair) in the passive with yapılmak:
Eğer asfalttaki çatlak tamir yapılmazsa, şeritler karışabilir.
This is slightly less formal but equally correct.