Portland's thrill-seeking bike riders have a new hobby. They call it tram-jacking.

You may've heard of tram jackers by another alias: the zoo bombers.

They take public transportation to the top of a hill then bomb down the hill at full speed on bicycles.

They've posted new video of themselves online. In the video, group of bike riders streams onto the tram with cameras in hand and music booming. This part is legal.

“But that assumes that the cyclists are responsible and give the respect to the patients and family members that they want for their right to ride the tram,” said Gary Granger, Director of Public Safety at OHSU.

Home video shows the group in February, parading the through a hospital hallway after leaving the tram. The music is still playing loudly as they stroll past hospital rooms.

“Some people are grieving because they may be ill up here. It's a hospital,” explained Granger.

Sam Adams, the city's transportation commissioner, says the group of mini-bike riders will need to stop coasting on sidewalks at OHSU, stop being loud, and stop risking their own health if they want to keep this new hobby.

“They've actually been pretty reasonable to work with,” he said. Granger hopes Adams is correct. “We ask people nicely not to do things they're not supposed to do that's the approach. At the end of the day we have the right to ask people to leave if they're disruptive.”

So far, tram jacking has been rare, happening on the occasional tram free-admission night.

OHSU plans to be proactive in communicating with the bike riders next time. The city is planning another tram free-admission night later this month.