DENVER -- Interstate 70 through the Colorado Mountains is known as a pipeline for the transportation of illegal immigrants.

That problem has never been more evident than it was last week.

On Tuesday, four Mexican nationals were killed in a crash near Idaho Springs. There were 11 others in the minivan who survived.

The driver of the minivan, 23-year-old Jose Franco Rodriquez, has been sent back to Mexico at least twice, including two months ago from Denver.

Authorities said the van was packed with illegal immigrants and Rodriquez is a suspected participant in a human smuggling ring.

Then Wednesday, another van full of 15 illegal immigrants stalled out on Interstate 70.

On Friday a third van full of 16 suspected illegal immigrants was stopped for driving 20 mph on the interstate.

Immigration enforcers said they take as many illegal immigrants into custody as possible, but it's simply impossible to detain them all.

Some residents in Idaho Springs said it all starts at the boarders.

"They wouldn't have the issue of the pipeline or the reckless driving or people who don't abide by our laws," said one resident.

Troopers said the I-70 pipeline problem isn't a lack of enforcement, but simple geography because Colorado is in the middle of much trafficking of immigrants from one state to another.

"What we try to do is go after the biggest threat to American public and that is criminal aliens," said Carl Rusnok of the U.S. Immigration and Customs Enforcement, or ICE.

The Colorado State Patrol said it will add an immigration enforcement unit to assist ICE next year. The unit was approved by lawmakers and is scheduled to begin functioning on July 1, 2007.