This depends on the specific facts of your case, including whether you are partially at fault for the accident, whether you had pre-existing injuries similar to those that you received in the accident, how badly you are injured, and how quickly you supply needed information to the attorney. If there are complicating factors that the insurance company can grasp onto to pay you less money, this can delay a fair settlement. Sometimes it takes a little bit more time to persuade an insurance company to rethink its position on a claim.
Also, some insurance companies take longer than others when handling personal injury claims. Even within the same insurance company, you will find that some claims adjusters are more responsive than others.