Complex sentence: The traditional locomotive builders were prohibited from building diesel road locomotives during this time, except for a few dual-service ALCO DL109s for the New Haven; steam locomotives could be built quickly and with fewer resources, and were the proven commodity at the time.
Split into simpler sentences: The traditional locomotive builders were prohibited from building diesel road locomotives during this time, except for a few dual-service ALCO DL109s for the New Haven. Steam locomotives could be built with fewer resources, and were the proven commodity at the time.