The prematurely decaying wood is worst at the Francisco station, where the entire platform will be replaced between September and the end of the year. Chopper 7HD found some work is already underway.
It will cost an estimated $150,000 to $175,000. The Chicago Tribune reports the CTA has already spent $350,000 to replace sections of wood at other stations.
The CTA says a fire retardant chemical used to treat the wood has not held up well when exposed to the elements.