Editor's note: This week, Ecotality's Steve Caratzas takes a look at one of the big problems with cleaning up emissions from school buses: missing federal money promised to states.  This post was originally published on Monday, May 7.

Though lawmakers passed a measure in 2005 to replace diesel school bus engines nationwide, the results have been paltry. Thus school children nationwide are still traveling on antiquated buses that produce pollutants some believe to be five times dirtier than outside air.

The issue: money. State officials are struggling to budget in the clean school bus initiatives, while Congress has yet to deliver the $1 billion it promised over five years to assist states in cleaning up diesel-powered vehicles – which includes school buses.

“I think at one time or another all our kids are going to be on a bus breathing that harmful air, and that should bother everybody,” said Karen Slay, a Lubbock, Texas, mother of four boys who have ridden buses. “In the big scheme of things, it doesn’t seem to be that expensive, to me, to retrofit these.”

High concentrations of diesel emissions (called particulates) are the cause of minor concerns like headaches, wheezing and dizziness. But recent studies indicate that particulates are also linked to asthma and lung cancer.

Filters of two different designs can reduce emissions on older buses: diesel particulate filters, installed in place of mufflers for $700 a piece, reduce tailpipe emissions by a whopping 85 percent; closed crankcase filtration systems, placed under the hood but with a staggering $7,500 price tag, reduce particulates by nearly 90 percent. Buses can be fitted with one or both types of filters.

An estimated 390,000 diesel school buses are on the road in the U.S., according to the EPA. Most newer buses were manufactured to meet stricter emissions guidelines and do not need filters. But about one-third of the nation’s diesel school bus fleet, or more than 100,000 buses, were manufactured before 1990 and are big polluters, according to the EPA.

California is leading the charge on this issue, as voters in that state last year approved $200 million to refurbish its school bus fleet.