 Accordingly, it was decided to update the ER1 trainsets with exits which were compatible with both high and low platforms; the updated design was to be known as the ER2.The new exits required changes to the underframe, which could have had deleterious consequences for the cars' structural integrity; to avoid this, the cars' side walls, headstocks, door frames, and head-end bulkheads (on cars with engineers' cabs) had to be reinforced.Also, to maximize commonality of parts with the ER9 AC electric trainsets (which were to be produced concurrently with the ER2 on the same assembly lines), the brakes were redesigned—instead of 1 master cylinder actuating all of a given car's brake shoes, 4 brake cylinders were installed (2 per truck).