The reason why an ARC Zone traffic ticket is considered to be more severe than a standard infraction of the law is because the city has determined that along this particular stretch of highway, there is a statistically higher rate of fatal accidents.
ARC stands for “Accident Reduction Corridor.” It is a mechanism put in place by the city of St. Louis (and participating municipalities) to try and reduce the high number of traffic accidents that occur annually along I-70 interstate that result in fatalities. From roughly St. Ann to the I-170 and I-70 intersection, there is a much stricter enforcement of the speed limit.
But getting pulled over in the ARC zone will normally entail a police officer who was initially parked on the side of the highway (with three or four squad cars behind it waiting their turn) pulling out behind you immediately, flashing his lights, and issuing the citation. This description is of course the normal way in which an officer of the law makes a regular stop, but the ticket he/she will give you as a result is far more expensive.