(CBS) — Nearly four months have passed since the embankment collapsed on the CTA’s Yellow Line, shutting it down. But at least another month of work remains.

It is not immediately obvious to those driving on McCormick Boulevard by the site of the embankment collapse but work is continuing seven days a week. CTA engineers say the Metropolitan Water Reclamation District (MWRD) underground dis-infection plant being built next to the ‘L’ line must be finished first, and that has been contractor Walsh Construction’s emphasis. But an MWRD spokesperson and CTA President Dorval Carter both say it remains on schedule.

Carter calls restoration of service “a top priority.”

Free shuttle buses and Skokie terminal parking remain, one of many costs MWRD is picking up as part of the repair project. A CTA spokesperson said that ridership on the buses is down at least 50 percent from the pre-collapse ridership of 2,900 daily riders on the Skokie Swift.

The collapse has affected CTA in many ways in addition to the loss of Yellow Line service. It has left the agency’s main repair shop isolated from the rest of the rapid transit system. Work continues at Skokie, which has also accepted the last 35 cars of its 714-car order of new rapid transit cars since the collapse occurred. The new ‘L’ cars, and other ‘L’ cars needing major repairs, must be trucked using a roundabout route between Skokie Shops and CTA’s 63rd Street lower yard, on the East 63rd branch of the Green Line.

A spokesperson said that some Skokie Shops personnel have been reassigned to help expedite work on ‘L’ cars at CTA’s other repair facilities.

Carter says disaster was narrowly averted in May and says CTA will test the embankment and tracks, once rebuilt, to make sure they will remain stable. The rebuilt line will be tested using trains weighted down to simulate full passenger loads.

CTA says the collapse did not damage the steel high bridge over McCormick Boulevard immediately to the east of the collapse. It remains unusable because of its proximity to the site of the collapse. Despite that, the transit agency continues to warn the curious not to trespass onto the Skokie Swift right-of-way, because the third rail remains energized much of the time.