Complex sentence: The distinctive Checker cabs were, due to their durable construction, phased out slowly, the last one being retired in July 1999, being over 20 years in service and nearly one million miles on its odometer.
Split into simpler sentences: The distinctive Checker cabs were, due to their durable construction, phased out slowly. The last one was retired in July 1999, after more than 20 years in service and with nearly one million miles on its odometer.