The short answer is that you need a rental car on Maui, and this page exists to explain the exceptions rather than to pretend there are many. The island is 48 miles across at its widest, its two halves are separate volcanoes joined by a low isthmus, and the things people fly here for are strung along its edges. Kahului Airport sits in the middle of the isthmus. From it, Kīhei is about thirty minutes, Wailea thirty-five, Kāʻanapali fifty to seventy depending on traffic, Haleakalā's summit around ninety minutes of climbing, and Hāna two and a half hours if you never stop, which you will.
Maui Bus exists, is genuinely inexpensive, and is a real service for people who live here. It runs fixed routes at a $2 fare per boarding with a $4 day pass, and two routes serve the airport. What it does not do is take visitors where visitors want to go. There is no bus to Haleakalā. There is no bus to Hāna. There is no route to Molokini's departure harbours at a useful hour, to the trailheads, to Honolua Bay, to ʻĪao Valley or to the Upcountry farms. There are no transfers between routes, so a two-bus journey costs two fares, and the airport routes run roughly every ninety minutes with a one-medium-bag limit. A car-free Maui trip is possible if you base yourself in one resort area and book tours with hotel pickup. It is not a general-purpose plan.
Three things about the roads are worth knowing before you pick up the keys. First, West Maui has effectively one road in and out. The Honoapiʻilani Highway runs along the Pali between Māʻalaea and Lahaina and it closes for rockfall, accidents and brush fire, occasionally for hours. If you are staying in Kāʻanapali or Kapalua, build a little slack into any plan that involves crossing to the other side of the island.
Second, two of Maui's most spectacular drives are excluded by most rental agreements. The Kahekili Highway around the north of West Maui is genuinely one lane with no guardrail in places. The unpaved southern section of the Piʻilani Highway beyond Kīpahulu, sometimes called the back road from Hāna, has variable surfaces and washes out. Read the contract. The exclusion is not decorative, and a recovery bill on Maui is not small.
Third, the Hāna Highway is a residential road that happens to be beautiful, and the etiquette there is real and noticed. Roughly 600 curves, 59 bridges with most of them one lane, and people who need to get to work along all of it. Pull over and let local traffic through, take turns at the bridges, and park only in actual pullouts.
Fuel is expensive by mainland standards and the supply thins east of Pāʻia, which is the last reliable petrol station before Hāna. Charge points for electric vehicles exist in the main towns and resorts and are sparse everywhere else. Plan around both.
