Metro stopped placing 1000-series railcars at the ends of trains primarily due to safety concerns and operational efficiency. The 1000-series cars, which were among the oldest in the fleet, had design limitations that made them less compatible with newer technologies and safety features found in more modern railcars.

One of the main issues was related to the braking system and overall structural integrity, which could pose a risk in the event of an emergency. By not placing these older cars at the ends, Metro aimed to enhance the safety of passengers and improve the reliability of service. Additionally, this decision allows for a more balanced distribution of newer, safer cars throughout the train, ensuring a more consistent experience for riders.

For more detailed information, you can refer to Metro's official announcements or news articles discussing their fleet management strategies. If you need further insights or specifics, feel free to ask!