Complex sentence: A handful of Standards became the first New York City subway cars to experiment with a public address system, as several cars received a loudspeaker telephone system in 1923-24 that was designed to aid conductors in making announcements.
Split into simpler sentences: A handful of Standards became the first New York City subway cars to experiment with a public address system. Several cars received a loudspeaker telephone system in 1923-24 to aid conductors in making announcements.