Why Does Highway Pace only show comparative information when the speed is above 30 Mph (48 km/h)?

Highway pace is intended to be used during steady highway driving. At lower speeds the comparative information is disabled to avoid distracting from road conditions.

Why does the speed shown by Highway Pace not match the speed shown by your car’s speedometer?

Highway Pace uses the speed returned from your phone’s GPS which is based on how far the phone has moved between readings. Your car’s speedometer may use a different method to calculate the speed such as monitoring the rotation of its wheels.