There is a way round this - using taxis and private hire vehicles
I have been studying this problem since 2004 and in 2005 came up with a solution. It is called a "Transit Exchange" and it allows people to share rides in *any* type of vehicle, be that a private car or a taxi.
To get round the insurance problem, use taxis or limousines. It is eminently doable. My company proved it in real conditions in 2006 and 2008.