The much stricter rules about driving to the summit area came about at roughly the same time as the TMT protests started. I'd have to spend some time looking to see what exactly prompted what, but some might remember the concerns that protesters near the VIS at ~9000 ft had introduced invasive species.
The dirt road was always off-limits to non-4WD cars but the rules were never enforced, so all sorts of cars went to the summit. Barely a week would go by without some local or tourist having their car towed from the summit. Many years ago, the cost was around $1000 but I suspect it's a lot more now. There were several accidents as well, nearly all involving burned-out brakes when driving down the mountain although there were a few collisions on the turnbacks and the odd incident such as the one HiloJulie mentions. These days the rules are much stricter. Observatory and tour vehicles, those that visit the summit regularly, have to go through inspections to make sure they are clean and free of invasive species before being allowed above the VIS (or more accurately, Hale Pohuku). Vehicles still break down though and there's usually at least one email sent out per month warning observatory staff of stalled vehicles and a tow truck on the way.
As for AWD cars, I'd be surprised if any are allowed up for the reasons Obie stated. Even in first gear on the way down, you have to use your brakes, so using 4WDs essential for safety; not to help deal with the dirt road but to handle driving steeply downhill for many miles.
And thanks again to HiloJulie for actually answering the OP. If anyone knows of any other companies that allow you to take their 4WD rental cars to the summit, please post them here.
The dirt road was always off-limits to non-4WD cars but the rules were never enforced, so all sorts of cars went to the summit. Barely a week would go by without some local or tourist having their car towed from the summit. Many years ago, the cost was around $1000 but I suspect it's a lot more now. There were several accidents as well, nearly all involving burned-out brakes when driving down the mountain although there were a few collisions on the turnbacks and the odd incident such as the one HiloJulie mentions. These days the rules are much stricter. Observatory and tour vehicles, those that visit the summit regularly, have to go through inspections to make sure they are clean and free of invasive species before being allowed above the VIS (or more accurately, Hale Pohuku). Vehicles still break down though and there's usually at least one email sent out per month warning observatory staff of stalled vehicles and a tow truck on the way.
As for AWD cars, I'd be surprised if any are allowed up for the reasons Obie stated. Even in first gear on the way down, you have to use your brakes, so using 4WDs essential for safety; not to help deal with the dirt road but to handle driving steeply downhill for many miles.
And thanks again to HiloJulie for actually answering the OP. If anyone knows of any other companies that allow you to take their 4WD rental cars to the summit, please post them here.