BRYN MAWR, Pa. (CBS) – If you “park and ride” along SEPTA Regional Rail lines, it could be a much more expensive trip than you expected.

An exclusive CBS 3 I-Team investigation reveals that since March 12th, riders have had catalytic converters, a pollution control device, stolen from beneath their vehicles.

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Most of the SEPTA riders victimized in lots at eight separate stations in Chester, Delaware and Montgomery counties had no idea the converters were stolen until they started their cars and they began roaring “like a motorboat” as one victim described it.

In almost all cases, our investigation found the riders left their cars in lots all day, discovering the thefts when they returned in the evening.

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Typically, it costs victims between $1,200 and $2,000 to replace the converters, which are part of the exhaust system.

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Experts say thieves take the converters because they contain precious metals such as platinum, and then resell them for between $100 and $200.

SEPTA officials say with metal prices soaring, converter thefts are spiking nationwide.

Currently SEPTA police do not patrol regional rail lots and there are no surveillance cameras.

Security is provided by local police departments in communities where stations are located.

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Reported by Walt Hunter, CBS 3