ANTI-ROAD racing police yesterday admitted that triad members took part in illegal races, but claimed there was no evidence schoolgirls were offered as ''prizes'' in bets. The head of the New Territories Anti-Road Racing Unit, Senior Superintendent Dave Thomas, also issued arrest figures which he said showed how successful the unit had been. He said virtually all road racing was either spontaneous or loosely arranged by groups of young men using up to seven vehicles, which were usually unmodified cars or motorcycles. ''Their main motivation seems to be show off to their girlfriends, who accompany them as passengers,'' he said. ''Although there has been speculation that females may be used as prizes, at present it is no more than speculation and there is no evidence to substantiate this. ''In addition, although there is evidence of individual triad members occasionally taking part in races there is no evidence they are involved in the organisation.'' According to Mr Thomas, nearly 500 people have been arrested for illegal road racing and/or reckless driving this year. Since January the unit has dealt with 34 road racing cases, resulting in the arrest of 240 people. In addition, 202 reckless driving cases have resulted in the arrest of a further 221 people. Twenty of the 34 road racing cases have been heard in court with all 37 people involved convicted, resulting in an average sentence of between two to four months' imprisonment, fines of up to $6,000, disqualification from driving for one year, and up to 120 hours of community service. All 221 people charged with reckless driving were convicted and given sentences of 12 months' disqualification and fines of between $3,000 and $4,000.