A preliminary report on the cause of the April 25 mudslide that buried a section of the No. 3 Freeway, killing four people, will be ready by May 7, Minister of Transportation and Communications Mao Chi-kuo said Thursday. The minister told the Transport Committee of the Legislative Yuan that an ad hoc panel of experts and scholars has been set up to probe the cause of the disaster. Mao said the panel will examine whether the freeway was designed, built and maintained according to norms, and whether those norms should be revamped. A detailed joint report and recommendations will be made by the panel, working with an international panel. In order to prevent similar mudslides on other freeways and railways under the jurisdiction of Ministery of Transportation and Communications, Mao said his ministry will conduct a survey before mid-May and install monitoring devices in places with signs of landslides, such as cracks triggered by strain on retaining walls, falling rocks and dilapidated protection devices. On the same occasion, Vice Minister of Transportation and Communications Chang Chiu-chun said it is impossible to determine whether human error was involved in the mudslide before the ad hoc panel presents its report. Lin Chao-chung, chief of the Central Geological Survey under the Ministry of Economic Affairs, repeated the vice minister's line while fielding lawmakers' questions, adding that the scene of the accident was located beneath a dip slope and was thereby vulnerable to mudslides. However, lawmaker Wong Chin-chu of the opposition Democratic Progressive Party (DPP) said human error was to blame after learning from Chang that no monitoring devices had been set up at the scene of Sunday's disaster. Mao said his ministry would help the families of the dead to claim compensation from the government, but stopped short of agreeing with lawmakers' demands of immediate compensation, saying legal procedure must be followed. Three DPP lawmakers, led by Chai Trong-rong, called for Mao's resignation for the disaster, saying he should kneel down to the victims to allay the anger of their families. The disaster took place when a retaining wall along the National Freeway No. 3 near Chidu in Taipei County collapsed without warning, burying a section of the freeway under hundred of thousands tons of earth. Three cars were covered by the earth, while many other vehicles escaped by the skin of their teeth. A round-the-clock rescue operation began immediately after the accident. The wreckage of the three cars and the four bodies of their occupants had been found, but the route was still closed to traffic. The accident has snarled traffic to and from Keelung, the port city at the beginning of the freeway, and President Ma Ying-jeou's administration -- which was criticized for its bungled relief efforts in the wake of Typhoon Morakot last August -- has tried much harder to cope with this most recent diaster. 