Complex sentence: While they may have been considered as the worst operating revenue service car when during the 1980s, many of the R10 cars were durable, and amazingly had outlasted the newer car fleets purchased and built afterward under the R11 through R22 contracts.
Split into simpler sentences: While they may have been considered as the worst operating revenue service car when during the 1980s, many of the R10 cars were durable. They did amazingly had outlasted the newer car fleets purchased and built afterward under the R11 through R22 contracts.