to employees, only processed passengers with a valid ticket are allowed inside the sterile lounge. Admittance into the sterile area is done in centralized security checkpoints in contrast to e.g. individual checkpoints at each gate. This allows for more efficient processing of passengers with fewer staff, as well as makes it possible to detect both delays and security threats well ahead of boarding. To ensure the viability of airport operations, new and innovative security systems are being developed. For instance, the old security checkpoints can be replaced by a "total security area" encompassing an entire airport, coupled with automatic surveillance of passengers from the moment they enter the airport until they embark on a plane. Passengers connecting to domestic flights from an international flight generally must take their checked luggage through customs and re-check their luggage at the domestic airline counter, requiring extra time in the process. In some cases in Europe, luggage can be transferred to the final destination even if it is a domestic connection. In some cases, travelers and the aircraft can clear customs and immigration at the departure airport. An example of this would be that some airports in Canada and Ireland, along with several other countries, have United States border preclearance facilities. This allows flights from those airports to fly into US airports that do not have customs and immigration facilities. Luggage from such flights can also be transferred to a final destination in the U.S. through the airport of entry. A crucial safety aspect of international airports is medical facilities and practices. In particular, controlling transmissible disease, such as SARS, is deemed important at international airports. While these standards are regulated by ICAO Standards And Recommended Practices (SARPs) and WHO's International Health Regulations (IHR), local authorities have considerable say in how they are implemented. Transportation Among the most important airport services are further transportation connections, including rail networks, taxi and shuttle services at curbside pick-up areas, and public buses. Large areas for automobile parking, often in co-located multi-storey car parks, are also typical to find at airports. Some airports provide shuttle services to parking garages for passengers and airport employees. Due to the very large scale of international airports, some have constructed shuttle services to transport passengers between terminals. Such systems operate for example, in Singapore Changi Airport and Zurich Airport. At some U.S. international airports, such as O'Hare International Airport in Chicago, some