I was just in Stockholm visiting a customer, and I noticed a new feature in my Volvo rental car: You could set the cruise control to a speed limit.
(apologies for the blurry picture, it was taken by my Narrative shirt pocket camera)
You drive the car as you would normally do, but when you approach the set speed, the car does not go any faster when you press the accelerator further. Unless you kick it down, in which case the car responds immediately.
This is an example of changing a well-known user experience slightly in order to “nudge” the driver to do the right thing. For more on this, I encourage you to read the book “Nudge” by Richard Taler and Cass Sunstein.
P.S. For my American friends, the number is km/h, not mph 😉