barrierless

• barrier-less

barrier +‎ -less

barrierless (not comparable)

1. Lacking barriers

   The world is increasingly barrierless.

   • 1979 August, Michael Harris, “A line for all reasons: the North Yorkshire Moors Railway”, in Railway World, page 412:

     High Mill crossing, at present gated and manually-operated, will become a barrierless rural-type crossing.

   • 2021 August 25, “Network News: New warnings to the public after trespass and near-miss incidents”, in RAIL, number 938, page 13:

     In Burneside in the Lake District on July 29, an incident took place at a barrierless level crossing on the Windermere branch that has been described by senior railway staff as one of the closest near misses they've ever seen.

2. (physical chemistry) Not requiring activation energy.
   • 1992, R.A. Marcus, Prabha Siddarth, “Theory of Electron Transfer Reactions and Comparison with Experiments”, in Elise Kochanski, editor, Photoprocesses in Transition Metal Complexes, Biosystems, and Other Molecules‎, page 63:

     The reaction is then barrierless, ie, ΔG* = 0, and the rate constant is a maximum for the given λ (Figure 6).

• barrierlessly
• barrierlessness