Помогите перевести The diesel locomotives are more costly than their predecessors, but they are available for work over

Помогите перевести предложение: The diesel and electric locomotives, which are taking the place of steam ones, are more costly than their predecessors, but they are available for work over much longer periods.
Тепловозы
и электровозы, занимающие места паровозов, являются более дорогостоящими, but they are available for work over much longer periods. Как правильно перевести --but they are available for work over much longer periods.