One rough rule of thumb for highways is that drivers should not drive for more than a minute without having a bit of curve. But highway curves, most of which can be driven much like any other section, are often not enough to keep a tired driver awake. Which is why engineers, starting in the 1980s, began to turn to roadside rumble strips. The results were striking. After they were installed on the Pennsylvania Turnpike, run-off-road crashes dropped 70 percent in the period studied.
