8% of allocated telephone numbers, based on historical call traffic averages.
A choke exchange has trunk facilities to other exchanges designed in a manner that high call volume is handled through the choke connection rather than overwhelming the rest of the local telephone network.
Other local exchanges have a limited number of direct trunks (junctions) to the choke exchange, which may only serve one or more customers, such as a radio station contest line, which may experience many simultaneous calls.
Examples of choke exchanges in North America have included: St. Louis, Missouri One of the early choke lines (exchanges) was instituted due to a widely advertised contest by a local radio station in the Miami/Fort Lauderdale area.
Due to the issues involved because of the "Last Contest", this may have been what caused the creation of the choke exchanges.