Congestion at the summit of Haleakala has increased during the last few years, in order to better preserve the area and to maintain safety of all guests the Haleakala National Park administration has introduced an advanced reservations process for those arriving in a personal or rental vehicle.
While the fee remains nominal, the process itself should help alleviate some of the congestion. The site is only rated for 150 vehicle, a fair number to begin.
It should only (at this time) affect arrivals between 3-7AM.
Tickets can be arranged through the National Parks site roughly 60 days in advance of your planned arrival, a second opportunity may exist in last-minute openings. The registration is set to be in addition to fees for a vehicle and only designed to better moderate traffic conditions at the top!