The given sentence is an example of a complex sentence.
A complex sentence is a sentence that consists of one independent clause and one or more dependent (subordinate) clauses.
An independent clause is a clause that can stand alone as a sentence. Every sentence must contain a subject and predicate and express a complete thought. Independent clauses fulfill these criteria while subordinate clauses don't. This is why they can't stand alone as a sentence. Their purpose is to provide additional information about what is stated in the independent clause.
The given sentence consists of two clauses:
<em>After violating the traffic signal, </em>- subordinate clause
<em>He hit a car coming from the other side.</em> - independent clause
