So me, , And, can interpert this series in their own ways
ep1 is just 11 and heng laying rails but fail badly
ep2 is when nole shows up and he with flatbeds are too heavy for the bridge and it breaks under him
ep3 is when keithen arrives and does most of the work but meeses up so bad everything becomes a comical explosion (this is not permenant just a silly gag)
ep4 is when the railway is finished beimg built (or rebuilt) but the hill the branchline is on creates an avalanche and the four engine run for their life