This is a list of broadcast station classes applicable in much of North America under international agreements between the United States, Canada and Mexico. Effective radiated power (ERP) and height above average terrain (HAAT) are listed unless otherwise noted. All radio and television stations within of the US-Canada or US-Mexico border must get approval by both the domestic and foreign agency. These agencies are Industry Canada/Canadian Radio-television and Telecommunications Commission (CRTC) in Canada, the Federal Communications Commission (FCC) in the US, and the Federal Telecommunications Institute (IFT) in Mexico. AM Station class descriptions All domestic (United States) AM stations are classified as A, B, C, or D. A (formerly I) — clear-channel stations — 10 kW to 50 kW, 24 hours. Class A stations are only protected within a radius of the transmitter site. The old Class I was divided into three: Class I-A, I-B and I-N. NARBA distinguished between Class I-A, which were true clear-channel stations that did not share their channel with another Class I station, and Class I-B, in which a station operated with 50 kW at night but shared its channel with at least one other I-B station, requiring directional operation. This distinction was superseded by the Regional Agreement for the Medium Frequency Broadcasting Service in Region 2 (Rio Agreement), which instituted the current class system. The former Class I-As are omnidirectional, with the exception of 870 WWL New Orleans and 1030 WBZ Boston, which use directional antennas to put a better signal over their largest population areas. Most former Class I-Bs are directional at night, although a few are also directional during days. (A handful of I-Bs did not have to use directional antennas: 680 KNBR San Francisco, 810 WGY Schenectady, 850 KOA Denver, 940 XEQ Mexico City, 1070 KNX Los Angeles and 1070 CBA Moncton. KNX and CBA were far enough apart that both could operate without using a directional antenna. XEQ is far enough from Montreal that it did not need a directional antenna. KNBR and KOA are the only Class Is on their frequency but share those frequencies with several Class II-Bs.) Former Class I-N stations exist only in Alaska, where they are too remote to interfere with other clear-channel stations in the contiguous 48 states. They are only held to Class B efficiency standards (although higher efficiency is acceptable). No new Class A stations are licensed in the conterminous United States,