Speed limit

From Memory Alpha, the free Star Trek reference

Certain authorities impose speed limits in certain locations, limiting the warp factor at which starships can transit the area.

The Hekaran scientist Serova opened a subspace rift in the Hekaran sector in 2370, demonstrating that conventional warp engines caused damage to the fabric of spacetime. The Federation Council imposed a speed restriction of warp factor 5 on all Federation vessels in all but extreme emergencies. (TNG: "Force of Nature")

In 2378, The Doctor, disguised as Kathryn Janeway, informed the crew that hostile ecological extremist aliens had completely outlawed conventional warp drive inside their territory. They supposedly also believed all conventional warp drives cause damage to subspace, and had ordered the warp core of the USS Voyager to be ejected. (VOY: "Renaissance Man")

The Doctor also referred to a fictional type of warp drive, supposedly decades ahead of Federation technology, called transphasic warp drive that didn't cause the damage. (VOY: "Renaissance Man")

Known regions of space where warp speeds were physically limited by local subspace effects include the Hekaras Corridor and the Lantaru sector. (VOY: "The Omega Directive")