Haleakala by car
You need some sort of motorized vehicle to go
to Haleakala so I recommend getting a rental car. There are also
tour operators that offer bus rides to Haleakala for those who
are scared of the drive. The road climbs quickly and is twisting
and narrow at times. You will see numerous signs telling motorists
to watch out for cyclists, which use this road to come down from
the summit (and if you come early you'll also see the cyclists).
There is no need for a 4-wheel drive in my opinion, any car can
make the drive.