Frozen Slime Block

There is no friction here at all. Release the movement key and you keep whatever speed you had, right up until the run of blocks ends or something stops you. Stepping up single block rises along the way costs you nothing either.

The catch is that speed has to come from somewhere first, because ice does not accelerate you, it only refuses to slow you down. Lay a short stretch of Asphalt Block at the start of the run and let the ice hold that speed for the rest of the distance. You can also leave every other tile empty and the slide continues, which halves the material a long highway costs. Fill those gaps with any other block and the whole thing stops working.

• Dash speed from Tabi, the Shield of Cthulhu or Solar Flare armor bleeds off the moment you land on ice.
• Top speed built up on asphalt drops back slightly once you cross over.
• Minecarts ignore the surface entirely and coast to a stop as normal.
• Ice Skates do nothing for the slide itself, though they do give you back some steering.

Grappling forward and cutting the hook before it finishes reeling you in is a cheap launch for a sky road. Put doors at the places you want to stop, since a door can be grappled and opened at full speed. The blocks read as ice for anything that cares about surfaces but will not turn the area into a Snow biome.