That's an interesting question because 'Collided' by Lauren Asher sits in a weird in-between space that's sort of both. On one hand, it's absolutely part of a series—'The Dirty Air' series, to be exact. There are four books: 'Throttled', 'Collided', 'Wrecked', and 'Widowed'. Each one follows a different Formula 1 driver, so 'Collided' is Liam's story, the second brother. So yes, it's clearly a series installment.
But here's where it gets a bit more nuanced, and why I think people ask this. You can read 'Collided' on its own without reading 'Throttled' first. The central romance between Liam and Sophia is completely self-contained. You get their full enemies-to-lovers, forced proximity arc right there in the book. All the major plot beats for their relationship are resolved within its pages. I know a few people who started with 'Collided' and didn't feel lost on the core romance.
That said, calling it a true standalone feels misleading. You'd miss a ton of context on the dynamic between the two brothers, Liam and Noah. Their rivalry and the fallout from book one is a major emotional undercurrent in Liam's motivations. The family drama with their dad also builds across the books. So while the love story is standalone-ish, the character arcs and series-wide plot are not. It's a 'soft standalone' in a very connected series, which I think is a pretty common and effective model in contemporary romance these days. My copy is pretty dog-eared from a couple re-reads, usually when I'm in the mood for a grumpy hero with a secret soft side.