Different lawyers will tell you different things, although you should talk with an attorney about specific situations.
Laws can be simply divided into criminal laws and civil laws. There is nothing about 'fraction' or 'nonfraction' in Washington law. A fraction is mathematically related.
Generally, 'criminal traffic' in WA means a traffic offense that carries criminal consequences, such as jail or prison time. In Superior Court, many traffic offenses are felonies, which means the penalties exceed more than one year imprisonment (except that some crimes heard in Superior Court may be misdemeanors or gross misdemeanors when coupled with a felony charge).
An infraction in WA is a law violation that is a civil offense - it may not carry jail time but there could be financial and other penalties. Many infractions, such as speeding or running a stop sign, are traffic-related, but other infractions such as open container or noise violations may have nothing to do with driving.