"If they are not on file, there's nothing we do," said Cedar Rapids Police Sgt. Cristy Hamblin, whose city has issued more than $2 million in tickets this year.
Lt. Rob Hansen, spokesman for Iowa Department of Public Safety, which includes the highway patrol and Division of Criminal Investigation, said it is a break that his department doesn't want.
"If one of our cars has an issue, send us the stuff, we'll take care of it," he said.
Hansen said the patrol has fewer unmarked vehicles than the data suggests after it recently took steps "to provide a more robust visual presence on the roadway system." He said its fleet manager will contact the DOT to remove more than 30 plates from the not-on-file designation because their vehicles now display official plates.
The data doesn't reflect the total number of vehicles, because some may have more than one plate that isn't on file. Agencies also aren't required to tell DOT when they stop using the plates.
DNR spokesman Kevin Baskins said its numbers are high because vehicles for game wardens have two plates with that designation. One includes the officer's badge number — such as C35 — and is routinely used. The other is an ordinary plate that is put on when they conduct investigative work, such as looking for hunting or fishing violations, he said.
The data shows little uniformity in which agencies get plates and how many. The Department of Corrections' 6th Judicial District, which includes parole and probation services in six counties around Cedar Rapids, has 38. The 5th Judicial District, which serves Des Moines and 16 counties, has seven.
The overall number — 3,218 — is a tiny fraction out of the 4 million registered vehicles in Iowa. Still, critics who argue that traffic cameras infringe on personal liberty have seized on the news.