The Boy Who Fell Down Exit 43 by Harriet Goodwin
Published by Stripes Publishing.

For a millionth of a second the car grazed the drenched moorland. If it had come down on any other patch of ground Finn would simply have been another statistic. Death by dangerous driving. But the car hit the surface of the Earth at Exit 43 … And at that moment, though no one yet knew it, the entire future of the Underworld changed course.
Finn Oliver knows he’ll never come to terms with his father’s death, but joy-riding over the moors in his mum’s beat-up old car is a quick fix of freedom and forgetting.
Until the accident happens and Finn finds himself hurtling through the wafer-thin divide between the worlds of the living and the dead.

About Harriet Goodwin

Harriet Goodwin lives in the middle of nowhere with her husband and four young children – and spends lots of time building dens in the garden. Some weekends she gets to dress up in lovely long dresses and sing concerts in big halls and churches and cathedrals. The rest of the time she writes her books in a special den of her own at the top of the garden.

http://www.harrietgoodwinbooks.com