There are three common scenarios of injury that occur and each present in different ways
There are macrotraumatic injuries that occur with immediate damage to the soft tissues where disruption to the soft tissues causes immediate pain and swelling that is easily recognizable to the patient and they usually seek care quickly ...

Patients are often sent to the Emergency Room or urgent care center where they are examined, x-rayed and told that there are no broken bones and that they have sprains, then prescribed medications and told that the pain will go away with time. They are then sometimes advised to use heat or ice (despite research showing that first 72 hours need to use ice). They may seek help with their family physician who treats the problem with medication primarily. Many times they are told that their family doctor will not see patients involved in a collision at all. Many family doctors do not get involved in this type of injury because their interest is more in sickness such as chest cold, flu, internal organ dysfunction, diseases etc.
They also as a whole do not like the difficulties of the paperwork, specialized reports, dealing with insurance companies, and attorneys etc. They also lack the treatment equipment needed and do not usually specialize in injury care. So the patient after a few weeks of living with the pain and taking medications that make it difficult for them to function at work they finally present to the Chiropractor for help. The Chiropractor is uniquely qualified for injury care and our clinic is unique among other Chiropractors. We have the knowledge, equipment, the training and most important the experience to get you back to your life as you were before the injury.
Car Wreck with Onset of Pain within the first week following the collision.
There are also microtraumatic injuries that occur when the forces of the collision causes small tears in the soft tissues so that small amounts bleeding occurs gradually over a period of time. This bleeding causes congestion and swelling in the soft tissues, and the pain is felt worse the next morning and gradually over the next few days to weeks. This causes the patient to seek care after a few days to a few weeks, or unfortunately sometimes not at all, because of the mistaken "maybe it will go away" mentality.
These patients need to be examined by a Chiropractor as soon as possible because the longer the time frame between injury and intervention the more difficult the problem is to alleviate. If this small amount bleeding is allowed to coagulate clot or solidify in the muscles and other soft tissues, with out proper treatment it will lead to adhesions and scar tissue in the muscle and fascia (sheath around and between muscle) which will cause limit range of motion of the muscle and the joints. This will cause tension and friction in the tendons, muscles, ligaments, and eventually bones and joints. Ultimately it will affect the nerves which is very undesirable. Over time it can lead to degenerative joint disease and other problems. The best thing is to get checked as soon as possible after the collision.
Car Wreck with Onset of Pain over a longer period of time, Weeks to Months
The third category is where the collision forces cause a change in the body which is subclinical (no symptoms are noticed). The cause of this bodily structural shift is mostly due to changes in the muscle. Then over time this unequal muscle tension and unequal muscle length causes the formation of fibrotic knots or trigger points in the muscle causing cramps and spasms. This causes the body to change very slowly adapting and changing to this "out of square" or "out of whack" imbalance of the body. This imbalance over time takes a toll on the body and because of altered weight distribution, friction in the tissues, and increasing strain on the muscles, tendons, and ligaments and the eventual scar tissue formation. Inflammation then occurs and the nerves become irritated and muscles become even more taut in a problematic cycle. The result is a person who doesn't even know why they have this painfull problem because they did not develop their symptoms for a extended period of time after the wreck, maybe weeks to months to years.
This is the most troubling injury because they will not relate their pain to the injury and will seek care often years later, after degenerative joint disease (wear and tear arthritis) has occurred with irreversible damage having occurred. These people can be helped later on, but not as well as they would have been, had they sought care earlier. Obviously all people need to be checked by a Chiropractor whom is a well qualified and skilled physician to treat soft tissue injuries from a motor vehicle accidents. Left untreated an injury such as those described above can lead to irreversible osteoarthritis, disability, chronic pain, altered posture and immobility just to mention a few of the potentialities of this lowered quality of life