The bus driver does his best to appear calm, but as he swerves his vehicle on a nearly empty road towards the border town of Matamoros thoughts of bus hijackings and massacres are clearly on his mind.
Authorities have found 126 bodies in the past weeks - including 10 on Wednesday - in area mass graves. The culprits, they say, are Los Zetas, a ruthless drug cartel run by ex-military commandos, and the victims were taken from passenger buses just like this one.
"Yes, I'm kind of afraid," said the driver, who refused to give his name.
"But one is here to work first, and I hope to God that nothing will happen to us."
There are only 15 customers aboard the Noreste passenger bus en route from San Fernando to Matamoros. Passengers include several women and at least two minors. The adults seem nervous.
State officials say that at least six passenger buses have been hijacked near San Fernando this year, though locals say the toll is higher.
This is the same area where the Zetas last year kidnapped and slaughtered 73 immigrants from Central and South America on their way to try to illegally cross the border into the United States.
"Once they stopped us on the road," said Jorge Enrique Gonzalez, a traveling salesman who works in the region.
"They looked like federal or military agents. At night we couldn't tell if they were good or bad. They asked us to identify ourselves, and asked some of us what our occupations were."
Gonzalez was spared, and now "I prefer to travel by day," he said.
It is unclear why the Zetas kidnap bus passengers along what the Mexican media has dubbed the "route of death."
Jaime Canseco, a senior official in the northeastern state of Tamaulipas, believes the gunmen could be looking for hostages for ransom, or could be recruiting hitmen and murdering those who refuse to join. They could also be forcing people to pay a toll to travel on the road.
The federal government on Tuesday said it was sending reinforcements to patrol the north-eastern highways, but it did not say how many troops would be sent beyond the 8,000 troops already in the region.
The bus stopped at several government roadblocks, so "things are calm for the time being," says the driver. "The problem is driving at night."
One of the three bus companies normally operating in the region has stopped service. The other two companies only drive buses during the day.
"We can't cancel routes because it would be turning our backs on our customers," said Abelardo Osuna with the Transpais bus line. Osuna said his company is instead re-routing the buses.
Since 2010, more than 1,600 people have died in Tamaulipas state in the turf war between the Zetas and their former employers, the Gulf cartel.
As the sun sets the passengers aboard the Noreste bus become more agitated.
"I haven't traveled in this area for 16 years," said a passenger heading back to the United States who only gave his name as Juan.
"Hopefully nothing will happen," he says, nervously checking his watch.
In Matamoros, a crowd of relatives of missing travelers gathered Wednesday at the city morgue, wondering if the bodies of their loved ones had been found in the mass graves.
"I just came here with the hope of finding the body of my husband, who left more than a year ago from Guanajuato," in central Mexico, said Juani Manriquez, 40.
Manriquez's husband had promised to call once he reached Matamoros, with plans to swim across the Rio Grande into the United States and make his way to Miami for work.
The call never came.
Manriquez is one of 136 people from around the country who has signed up with officials to see if any of the bodies belong to their missing relative.
At least 57 people from Guanajuato have filed cases of missing people in the last days, local media reported, and people from at least six other areas said they intend to travel to Matamoros searching for missing loved ones.
Experts are having difficulty identifying the bodies. There is not enough room in the amphitheater where the bodies are being kept, and a shortage of trained personnel to complete the task.
State prosecutors said that some of the bodies they have found have been buried for more than a year.
"Don't be surprise, we could eventually find more than 180 bodies," said a local investigator, speaking on condition of anonymity.
There are so many bodies that a refrigerated truck was being rushed from Mexico City, because the local morgue was overflowing.