If you're moving to the USA and planning to drive then speed limits and their enforcement in the USA will be an important thing to be aware of. Speeding is generally taken much more seriously in the US than in many other countries.
Speed limits vary across US states and are generally signposted. The recommended government speed limit on freeways is 55mph, although this has been increased on rural highways to 65mph in most states. Enforcement of the speed limits on the freeways is fairly relaxed, resulting in drivers typically averaging around 5-10mph above this. However, off the freeways speed limits are strictly enforced and care needs to be taken - particularly in school zones, where speeding is seen as a serious offence. Extra care should also be taken in small towns where speed limits can sometimes be as low as 25mph.
As in the UK, radar guns and traps are used widely to monitor motorists' speeds by the police. The use of marked and unmarked cars, backed up by helicopter or light aircraft, is also prevalent. Whilst most states warn of upcoming radar traps, this is not always the case - so care should be taken at all times.
Speed cameras, used successfully in the UK for many years, are now also becoming increasing popular across US states as another method of calming and monitoring traffic speeds. Satellite Navigation systems in the UK invariably warn of upcoming speed cameras, and whilst these are permitted in most US states, radar jamming devices are illegal and should never be used. You should also beware of warning other drivers of speed traps by flashing your headlights - just like here in the UK, this is also illegal in the US and will result in you getting a fine.
Wherever you're moving to in America, if you're planning to drive when you get there then make sure you're thoroughly aware of the local speed limits and their enforcement in the USA before you go - just remember that these can vary from state to state.