This is the 11479th most frequent Polish word.
jechały
"Jechały" means "they were going" or "they went" (by vehicle).
In this sentence, 'jechały' refers to the action of vehicles (plural), indicating they were moving.
Samochody jechały szybko po autostradzie.
The cars were driving fast on the highway.
Here, 'jechały' describes the movement of the girls, specifying they were riding bicycles.
Dziewczyny jechały rowerami przez park.
The girls were riding bicycles through the park.
In this instance, 'jechały' is used for trains, emphasizing their scheduled later movement.