The lion kingdom gathered individuals weren't allowed to photograph their demo rides through the boring tunnel. The sled idea gave way to retrofitting existing cars with side wheels in front. It sounded rather bumpy, since the side wheels on a monorail are pneumatic, with their own suspension systems. The only video of a real trip was on CBS & like any supposedly autonomous car, it was actually being driven by a hipster who was always kept just out of frame. It was implied that the demo would be some fully automated vision of the future, but reality was more smoke & mirrors.
The side wheels do have some compliance. On the one paw, they avoided the complexity of distributing sleds to all the tunnels. On the other paw, it wouldn't have taken a massive sled to do what the side wheels are doing.