So yet another elderly driver caused a fatal collision. We really, really need to retest motorists for driving knowledge at each and every renewal, shorten the renewal times and retest for driving skills at each renewal after age 55. Sure, it would add a small sum to the cost and will surely inconvenience many people who find themselves reading the tiny pamphlet the DMV publishes after they fail the knowledge test, but that seems like a trivial cost to save lives.