The Brighton Beach line began in 1878 as the Brooklyn, Flatbush, and Coney Island RR steam train. It was a surface line from Prospect Park to the Brighton Beach Hotel, which was owned by the railroad. Below is a picture of the hotel.
The line was later extended to Atlantic Avenue, where it connected with the main line of the LIRR. Because the LIRR had a competing hotel, there was a dispute and the LIRR terminated the connection. The map below shows the connection of the BF&CI RR to the LIRR tracks. The competing NY & Manhattan Beach RR is also shown.
Meanwhile, the BF&CI RR had re-organized as the Brooklyn & Brighton Beach RR, and arranged for through service with the Franklin Street El. By 1900, the B&BB RR was electrified, there was through-service to Manhattan, and it was a commuter line rather than a seasonal line. By 1907, all grade crossings were eliminated.
It is an interesting line to rail-fans because its track includes tunnel, open cut, embankment, and elevated sections. The placement of these track sections roughly corresponds to the decreasing elevation of the glacial moraine as it slopes southward toward the ocean. The map below shows the location of the different types of track.