Metra eased its bikes-on-board policy Tuesday, eliminating an automatic ban of all bikes during three big Chicago special events and allowing bikes on trains that arrive downtown before 6:30 a.m.

But Metra officials cautioned that they still reserved the right to boot bicyclists and their bikes if trains become too crowded during their rides.

Previously, bikes were prohibited during three big Chicago festivals — Lollapalooza, Taste of Chicago and the Air and Water Show. However, on Tuesday Metra replaced those blanket “blackout” bans with a “warning,” meaning that bike admissions would be up to train crews.

During special event “warning” dates, “Metra will advise passengers through alerts, announcements and its webs site that there is the potential that bikes cannot be accommodated on the initial or return trip,” Metra said in a news release.

In addition, Metra eased some of its rush-hour bike ban, allowing bikes on board during some of the very early morning rush — for trains that arrive downtown at or before 6:30 a.m.

Metra spokeswoman Meg Thomas-Reile additionally cautioned that if bicyclists get on a train with adequate room during the early morning rush or a special event, but during their ride the train becomes too crowded to accommodate bikes, they could be asked to depart. No refunds in such circumstances are granted, but bicyclists would not be charged a second fare on the next train, Thomas-Reile said.

“In these cases, the bicyclist is not charged for a new ticket and the train crew informs the crew of the next train following that one that there is a cyclist waiting to board,” Thomas-Reile said.

The more bike-friendly policy followed discussions with Chicago’s Active Transportation Alliance, Thomas-Reile said. The Alliance’s campaign director, Kyle Whitehead, said the alliance was pleased to hear about the elimination of some blackout periods, as some Alliance bicyclists in the past had wanted to board Metra trains headed out of Chicago on the first night of Lollapalooza, but were banned from doing so.

“Next year, if there’s available space during Lollapalooza, bicyclists will be able to bring their bikes on board,” Whitehead said. “Under the current policy, for that whole weekend, there’s no wiggle room. Not all those trains are always completely full.”