Empty seats are a waste of space. Filling a car with passengers can help offset the price of filling it with fuel. Even if you can't split the costs, it's a chance to cut your carbon footprint. It seems unreasonable to expect kids to chip in for fuel, but you can't really leave them behind.
The polar bears will thank you.
3. Hitch
It used to be the reserve of backpackers and sociopaths, however hitch hiking is having a resurgence on New Zealand roads. This is partially thanks to the mobile revolution. Apps like Chariot (getchariot.com) help drivers and hitchers find spare seats going in their direction. Beyond just 'thumbing it' apps can be a cheaper, fairer, often safer way of getting a lift to where you're going.
But of course that's not always an option for families or a group of travellers, unless you flag down a passing minibus.
4. Ditch the car and fly
Auckland to Taranaki is the classic Kiwi road trip. The six-hour car journey leads to the beaches round New Plymouth or simply to bathe in the majesty of Mt Egmont.
But sometimes you just want to get there. It might surprise road users to know you can do far quicker and more cheaply by air. The 400km will cost around $90 in fuel one way, and the best part of half a day.