They seem to be, but that awful webiste says:
"On October 17, 1978 a third tunnel was discovered following th e 1975 testimony of defector Kim Bu-sung. Initial efforts to discover the tunnel failed until June 10, 1978, when an excavation hole was exploded, they started to dig a counter-tunnel which later reached the North's tunnel on October 17, 1978. It is about the same size as the 2nd Underground Tunnel, but would have been the most threatening tunnel if the North had used it to invade Seoul. According to Kim Bu-sung, North Korea planned to make five southern exits. Normally one or two were to be used, but in a decisive stage all were to be put into use. It was designed for both conventional warfare and guerrilla infiltration. The tunnel is 4 km south of Panmunjom and 44 km from Seoul. It is 73 meters underground and roughly 1,635 meters long. About 30,000 ranked, heavily-armed troops can pass per hour. "