Simplify the following text for a Grade 12 native English-speaking person.
Original: All of the SEPTA Regional Rail lines except for the Cynwyd Line pass completely through the four-track tunnel , which contains two underground stations - Suburban Station and Market East Station , and the above-ground upper-level concourse for the east-west commuter lines serving 30th Street Station .
Simplified: The Center City Commuter Connection connects the core SEPTA stations Market East Station , Suburban Station , and 30th Street Station .