As an alternative to solid fuel movement, the energy in coal can be sent indirectly to the point of end use via electrical transmission. Transmission of electricity can occur as either alternating or direct current, but in the United States it is usually done by high voltage alternating current. Electricity is normally transmitted at 138,000 volts (138 kv) near load centers, but is usually transmitted at either 345 kv or 765 kv over extended distances. Electricity transmission has been tested at 1,100 kv by the Bonneville Power Administration, and is now being transmitted at 1,500 kv in the Soviet Union. There are presently 360,000 miles of high-voltage transmission lines in the United States.Most extra-high-voltage transmission lines in the United States are in the east or on the west coast. These lines generate significant electric fields adjacent to the wires. As a result, the transmission towers must frequently be 200 to 300 feet tall to reduce electric field density to less than one volt per centimeter at ground Coal Transportation 69 level. The transmission lines generate ozone although not in large quantities.High-voltage, long-distance transmission lines also result in energy losses of about 1% per 100 miles. Long distance transmission is often not competitive with other coal energy transport modes at distances of greater than 300 miles.