That would be a fun ride down the grassy hill, but there appear to be fences on the eastern and western hills preventing users from going straight down and across the road. Esri World Imagery (Clarity) Beta shows a bridge going across, but this imagery is usually very old, and newer imagery (Esri - 2014) (PEMA - 2018-2020), and Bing (2023) show the bridge part removed and the fences put in on the hills. This photo from the Brookville Trail Hub Facebook page on May 3rd, 2024 seems to indicate that riders are to stop on the hill west of Arch Street Extension, dismount their bikes and walk down the hill near the underground pipeline in OSM. 
"Caution when descending from the trail to Arch St Extension"
https://www.facebook.com/photo/?fbid=459879950038257&set=pcb.459880063371579
I am not sure where or whether the trail continues east of Arch Street, because the locals on the Facebook page mention starting from Arch street, ex. "This is one reason the trail isn't as popular as it could be. It really needs better access and parking from Arch St."
https://www.facebook.com/BrookvilleTrailHub/photos/this-sign-will-help-hikers-from-brockway-find-five-bridges-trail-the-brockway-mu/502329405793311/?_rdr