Here is a link from the fia website with some HANS info:
http://www.fiainstitute.com/document...ans%20belts%22
Scroll down to page 4, section 2.5 where there is a description and illustration of a double shoulder belt system. This is an idea to consider for the new car's belt system. It may be a solution to the problem of the straps slipping off the HANS and it also seems like it would be a lot more comfortable for the driver.