The short answer is that whether a careless driver receives a ticket has little to do with proving a claim of negligence.
In many cases, police will choose not to cite a careless driver. It may be that there is insufficient evidence to prove a violation. It also may be a matter of department policy. Even if a driver received a citation, that fact, along with any conviction for a traffic offense is generally not admissible in another case involving an injury claim against that same driver. The rationale in the evidence code is that many people decide not to "fight" a traffic ticket, and for this reason, the mere conviction of a moving violation is not reliable evidence of negligent behavior.
However, when a careless driver receives a citation, and decides to contest the citation, some evidence may be helpful. For example, if the driver testifies in a court hearing, and that testimony is recorded, the testimony can be admitted in another trial. This is because the driver was placed under oath, and the law assumes that testimony under oath is generally reliable.
When we investigate a case, we determine whether not the negligent driver contested the citation, and in certain cases, we might even attend the court hearing.
If you have been in a collision in Oregon or Washington, and have questions about investigating liability, or proving the other parts of your case, call us at 503-325-8600. We offered 20 years of experience, and can explain how we investigate and pursue claims for injured drivers.