Even as Prince William County's crime rate dipped in 2006 to its lowest in six years, the number of street robberies and construction site burglaries continued to climb.

The crime rate, the number of crimes per 1,000 residents, was 21.6 in 2006, down markedly from 27.7 in 2001. In 2005, it was 22.8 per 1,000 residents.

The statistics were released during a news conference by Police Chief Charlie T. Deane. He said that among the department's findings, the most troublesome trend was the increase in robberies.

The number of robberies rose 40.4 percent from the previous year. Many victims are Hispanic immigrants walking alone and believed to be carrying large amounts of cash, he said. Of the 351 robberies reported, 83 percent were street robberies, with many involving Latino victims.

"The community is changing, and this is a phenomenon that we haven't seen before, and certainly never this dramatic of an increase in noncommercial robberies," Deane said.

He said police are seeing the trend continue this year. In response, the department started a robbery suppression initiative in September, a task force of about 20 officers who concentrate on high-risk areas. They have made 312 arrests, filed 503 charges and seized 41 firearms.

"They have been successful, but the robberies continue," Deane said, adding that police interrupted at least one robbery in progress and kept another from starting.

Two homicides last year began as robbery attempts against Latino men. In one, Serafin "Pedro" Alvarez Negrete, 32, was shot to death near the Woodbridge trailer park where he lived. He had left his wife and three children in Mexico to work here. Negrete was the 13th homicide in the county in 2006.

Overall, the county had 16 homicides last year, with one of the deaths occurring in 2005 and later declared a murder. Three of those homicide investigations remain open, including the shaken baby death of Abraham Isaac Roque at his babysitter's Haymarket home.

The number of traffic fatalities rose from 26 in 2005 to 35 last year. Six were pedestrians, six were on motorcycles and, of those driving, more than half were not wearing a seat belt.

After robberies, police saw the next-largest increase in burglaries, many occurring at construction sites. Last year, there were 1,389 burglaries, up from 1,101 in 2005. The department is trying to address the issue by working with the community, builders and construction companies, according to the crime report.

Calls for service also increased from 208,676 in 2005 to 222,818 in 2006. Police made more arrests, filing charges against 13,734 people, up from 12,761 in 2005. Police attribute the increase to more arrests of juveniles for serious offenses.