The most common and most likely answer to this crossword clue is the 8 letter word TOBOGGAN
I've seen this crossword clue in The Guardian
T
O
B
O
G
G
A
N
More clues leading to the result TOBOGGAN
- Vehicle sliding in the direction of marsh, horse backing
- Somehow got bag on sledge
- Got upset about facilities on a new downhill ride
- Boat going off? I dumped sledge
- Vehicle horse pulled back to marsh, initially
- Slough introduced to exotic tango — this goes downhill fast
- Vehicle to bring back horse beyond marsh
- Desperately got bag on sledge
- Winter transport with ancient outfit going round Slough North
- Awkwardly got bag on winter vehicle
Buddy explains!

The straight part
We know that "Vehicle/Vehicle" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case vehicle/vehicle = toboggan.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does TOBOGGAN mean?
TOBOGGAN noun- A long sled without runners, with the front end curled upwards, which may be pulled across snow by a cord or used to coast down hills.
- A similar sled of wood, pulled by dogs, possibly with steel runners, made to transport cargo.
- Something which, once it starts going (figuratively) downhill, is unstoppable until it reaches the bottom.
- (especially South Carolina, West Virginia) A knit cap, designed to provide warmth in cold weather.
- To slide down a hill on a toboggan or other object.
- To go downhill unstoppably until one reaches the bottom.