San Francisco already has cable cars, with cables running up the hill. Something like this could easily be done for the steeper hills without too much additional cost - in terms of material i.e. The legal costs would go through the roof though - it would never be accepted on that basis. I still remember the reaction I got from the Foster City parks and rec committee about having a light installed in children's playgrounds so that they can be used in the evenings during the winter months ..