I found a work-around for some of the vehicle problems in the SL Forum. MB Robonaught wrote:
While many of the problems with vehicles used on Pathfinder have been addressed to help with older created cars, there remains a few issues that need serious attention for newer Mesh cars. As per SVC-8048 I have discovered that if a builder uses at least 4 contact points with linden ground where all 4 are set to Convex hull the car will not sink. A single prim does not appear to have the buoyancy to ride above the edge of the land no matter what the size of the prim.
For those that run race tracks, we’ve found that volume detect is handled in a much different way. When a collision occurs between a physical vehicle and a prim that uses llVomumeDetect prim, size matters. For example if a prim that measures 0.5m x 1.0m x 10.0m is used it will randomly trigger a collision event (PATHBUG-156) making the car suddenly jump or veer off to one side. A fix for this for now is to make the prims as small as possible, such as using a 0.05m x 0.05m x 10.0m prim size instead of the above. Another option is to drive over instead of through the prim. (Reference)
My friends that work with vehicles are experimenting to see what works. So, I’m not testing vehicles. I can fly and don’t really need a vehicle. I know for many the various vehicle experiences in SL are a primary reason to be here.