Speeding by drivers is probably the greatest single safety issue for those of us in the bike and pedestrian advocacy world. Yes, many will say that this is because that for 50 years we've design roads with only the safe, smooth and efficient flow of motor vehicle traffic in mind. There is no argument there. However, I think one factor that many people are forgetting are the cars themselves and how advances in automotive technology have enabled drivers to drive faster.
When many roadway design practices became the standards we use today, cars were much less capable machines. Think about it. Cars back in the 1960's and 1970's would start to shake and rattle at speeds above 60mph. By contrast today, the average car is a highly refined and incredibly well engineered machine capable of performance well beyond all but the most exotic sports cars from 30 or 40 years ago. They can accelerated faster, corner at higher g-forces, brake quicker all with a suspension and acoustic dampening that greatly trivializes speeds.
So my point is this. Roadway design speeds derived from standards established 40 years ago can no longer be valid with today's modern cars. A road that was designed to become uncomfortable for the driver at 45mph 40 years ago is likely not to seem uncomfortable until speeds exceed 65mph in a modern car today.
All the more reason to start engineering roadways for the actual speeds that transportation officials want people to drive.