Probably it is hard to find a road with very smooth surface. It wears out during time and then your drive becomes bumpy. Curious how bumpy it is? Then check out following project that measures this and even overlays on a map. To achieve this, techbitar used several building blocks including: Arduino, GPS module, SD card and XYZ accelerometer.
In order to measure bumps – only Z axis is needed. Arduino reads accelerometer data and packs it in to SD card along with GPS location and time stamps. In order to overlay data on map, he used GPSvisualizer.com that makes this easy task. This device may be used for fun but also for scanning road conditions or terrain mapping.