- Twenty cars line up between police cruisers in a violent northeastern Mexican city, ready to be escorted at high speed across a notorious "death highway" infested with gangs that kill and kidnap.
Many are Mexican migrants who drove across the border to Matamoros from the United States, bearing gifts for their families for the Christmas holidays.
Others are local residents who know the dangers they face driving across Tamaulipas, the state with the highest number of missing people in Mexico -- 5,000 out of 26,000 nationally -- and regular drug cartel battles.
With that in mind, the federal police launched "Operation Tread" in 2013 to escort civilian cars across Route 101, a ghostly highway with closed or deserted restaurants and businesses along the way. Things here are so bad, it is known as "death highway."
Carlos Ortega, a 55-year-old gardener who drove from the northeastern US state of New Jersey, said he learned about the operation in a flier that was handed to him after he crossed the border from Brownsville, Texas.
"I'm here because I'm afraid of the problems out there, like robberies, attacks. They take cars and money. You can't travel calmly. We need this operation," he said as he headed to Puebla in central Mexico in a sport utility vehicle with his daughter and two friends.
Tamaulipas is home to the Gulf and Zetas drug cartels, two criminal groups that were once allies but have fought brutal turf wars in recent years.
While they have both been weakened by the captures or killings of top leaders, their members still sow fear in the population.
A man who lives in Texas said he was stopped at gunpoint three times in past trips across Tamaulipas.
"They had large guns. They made me get out and they said they wanted my SUV. I was with my family. I told them, 'I don't have anything against you. I'd rather pay an extortion fee,'" he said.
He didn't know whether they were cartel henchmen or common criminals. But he said they ask travelers to give them between $30 and $70.
On this trip, his car was loaded with toys, bags and boxes with US goods. He pulled over behind the lead police cruiser, but he was nervous despite the escort.
"If there's a fight, the cruiser in front of us won't do much against 10 SUVs that come to steal," the Texas man said.
- 'Safe point' -
After the 9:00 am rendezvous, the caravan set off on its 300-kilometer (185-mile) trip to the state capital, Tamaulipas, a nonstop ride with no bathroom breaks.
The officers were armed with assault rifles as they began to speed down the highway, with little space between the cars following behind them.
The caravan reaches cruising speeds of 100 kilometers per hour, going faster in some stretches.
For those who dare to drive without the police escort, the authorities set up a "safe point" at a gasoline station guarded by police and soldiers so that people can fill their tanks and stretch their legs.
The police caravan sped up as it approached San Fernando, the most dreaded part of the trip. It was there that suspected Zetas members slaughtered 72 Central and South American migrants in August 2010.
"San Fernando is the hardest part. There are kidnappings there. They take your car and rob you," said Rafael Portales, 37, who buys cars in the United States to sell them in Mexico.
Near Ciudad Victoria, the driver of the lead police car waved his hand outside his window to signal the end of "Operation Tread."
"Every man for himself from here. May God bless us," said the Texas man as he headed on to another city in his SUV.
- Relatives of the missing -
In Ciudad Victoria, families of some of the thousands of missing people shared their stories.
Carlota Hernandez, 42, said her husband Livorio and son Jorge disappeared along with a neighbor in August 2013 after they went to buy a car part at a junkyard.
"They were fixing the neighbor's car. They went to the junkyard and never came back," she told AFP.
Days after their disappearance, the father and son's belongings were found in a house used by criminals to hold kidnapping victims.
"Four people were arrested. I spoke with them so they would tell me where they are, but they said they knew nothing," Hernandez recalled.
She never got a call asking for a ransom. Hernandez thinks they might have been taken away to be forced into joining the gang, but she really fears the worst.
Her story is only one of many.
Guillermo Gutierrez Riestra, founder of the group Families and Friends of the Disappeared in Tamaulipas, said the real number of missing is 11,000, twice the official figure.
His daughter was 19 when she was kidnapped in 2011.
"People don't file complaints," he lamented.
"Most disappearances happen on the roads. A Zetas chief was arrested and they found 50 driving licenses on him, which indicates that most were kidnapped on the highway," Gutierrez said.
"They could be truck drivers, blue-collar workers, white-collar workers, academics and migrants."