CHICAGO (CBS) — Nearly two years of delays begin Monday morning for rush hour riders on the CTA’s Red Line and Purple Express trains.

Demolition crews began working over the weekend where the southbound express track used to sit at Wilson, as the $203 million reconstruction of the 90-year-old station enters a new phase.

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Each of the tracks is being replaced. So, for the first two rounds, all southbound Red and Purple Line trains must share one track. Express trains inbound in the morning only will add stops at Wilson, Sheridan and Addison.

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The CTA said the same number of trains will run, but schedules will vary “slightly.” Officials predicted delays of 2-4 minutes on 95th-bound Red Line trains and 4-6 minutes on Purple Express trains.

The tracks above the station will be replaced one at a time, with construction to continue until late 2017.

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The transit agency said the benefit for long-suffering riders will be a modern, spacious and accessible station when the project is completed. The CTA also has predicted the area will become an economic anchor for the community.