There is a numerical value, but it's based on sentencing data. The method is to take all of the convictions for the various offences under the UCR2 violation codes—there are about 130 different violations—to track all of the convictions for those violations, identify how many were sentenced to custody, and use the average sentence, excluding outliers, to come up with a weight for that violation. That weight becomes a numerical value for the offence.
On April 20th, 2010. See this statement in context.