HIGHWAY OF TEARS.

Less than a year after her 15-year-old cousin vanished, Delphine Nikal, 16, was last seen hitchhiking from this isolated northern Canadian town on a spring morning in 1990.

Ramona Wilson, 16, a member of her high school baseball team, left home one Saturday night in June 1994 to attend a dance a few towns away. She never arrived. Her remains were found 10 months later near the local airport.

Tamara Chipman, 22, disappeared in 2005, leaving behind a toddler. "She's still missing," Gladys Radek, her aunt, said. "It'll be 11 years in September."

Dozens of Canadian women and girls, most of them indigenous, have disappeared or been murdered near Highway 16, a remote ribbon of asphalt that bisects British Columbia and snakes past thick forests, logging towns and impoverished Indian reserves on its way to the Pacific Ocean. So many women and girls have vanished or turned up dead along one stretch of the road that residents call it the Highway of Tears.

A special unit formed by the Royal Canadian Mounted Police officially linked 18 such cases from 1969 to 2006 to this part of the highway and two connecting arteries. More women have vanished since then, and community activists and relatives of the missing say they believe the total is closer to 50. Almost all the cases remain unsolved.

The Highway of Tears and the disappearances of the indigenous women have become a political scandal in British Columbia. But those cases are just a small fraction of the number who have been murdered or disappeared nationwide. The Royal Canadian Mounted Police have officially counted about 1,200 cases over the past three decades,but research by the Native Women's Association of Canada suggests the total number could be as high as 4,000.

In December, after years of refusal by his conservative predecessor, Prime Minister Justin Trudeau announced a long-awaited national inquiry into the disappearances and murders of indigenous women.

The inquiry, set to cost 40 million Canadian dollars ($31 million), is part of Mr. Trudeau's promise of a "total renewal" of Canada's relationship with its indigenous citizens, and it comes at a critical time.

Aboriginal women and girls make up about 4 percent of the total female population of Canada but 16 percent of all female homicides, according to government statistics.

Carolyn Bennett, the minister of indigenous and northern affairs, has spent months traveling across the country to consult with indigenous communities. During her meetings, families and survivors have complained of racism and sexism by the police, who she said treated the deaths of indigenous women "as inevitable, as if their lives mattered less."

"What's clear is the uneven application of justice," Ms. Bennett said.

One reason to doubt the estimate by the Royal Canadian Mounted Police, she said, is that the police often immediately deemed the women's deaths to be suicides, drug overdoses or accidents, over the protests of relatives who suspected foul play. "There was no investigation," she said, citing one recent case. "The file folder's empty."

A United Nations report last year described measures by the previous government to protect aboriginal women from harm as "inadequate" and said that the lack of an inquiry into the murders and disappearances constituted "grave violations" of the women's human rights. Failures by law enforcement, it added, had "resulted in impunity."

Ms. Radek, a co-founder of Tears4Justice, an advocacy organization, said, "When it comes to the missing, racism runs deep."

The federal government has allocated 8.4 billion Canadian dollars ($6.4 billion) over five years to aid indigenous communities, which have disproportionately high levels of poverty, incarceration, alcoholism and substance abuse, and often lack basic necessities like safe drinking water.

Ms. Bennett said the breakdown in aboriginal communities was the product of generations of socioeconomic marginalization and trauma tied to government policies. Particularly damaging was a state-financed, church-run boarding school system for aboriginal children who were forcibly taken from their families by officers of the Royal Canadian Mounted Police. Many of the 150,000 children who were sent to residential schools over a century became victims of physical and sexual abuse. The program was fully shut down in the mid-1990s.

Covering 450 miles between the city of Prince George and the Pacific port of Prince Rupert, the Highway of Tears is both a microcosm of Canada's painful indigenous legacy and a serious test for Mr. Trudeau as he tries to repair the country's relationship with aboriginal people.

On a recent journey along Highway 16, scenes of stunning wilderness were flecked by indigenous communities reeling from economic decay and the anguished memories of missing and murdered women.

A few miles outside Prince George, the highway plunges into thick forests veined with logging roads and the occasional "moose crossing" sign. "Girls Don't Hitchhike on the Highway of Tears," reads a large yellow billboard alongside the road farther north. "Killer on the Loose!"

As a bald eagle soared overhead, Brenda Wilson, 49, the Highway of Tears coordinator for Carrier Sekani Family Services and the sister of one of the victims, gestured to the wall of evergreens that flank the road. "The trees are really dense here, so if you're looking for someone, it's pretty hard to find them," she said, listing the names of several women who are still missing.

The provincial government announced plans in December to improve safety along Highway 16, including funds for traffic cameras and vehicles for indigenous communities. But little has changed on the road, which lacks lighting or any public transportation other than infrequent Greyhound bus service that does not reach remote communities.

The perils do not stop desperate people from thumbing rides in a region where public transportation is practically nonexistent. Just outside the village of Burns Lake, Drucella Joseph, 25, an unemployed aboriginal woman, eagerly climbed into the back of a passing car along with her boyfriend, Corey Coombes. "Friends will drive me when I really need a ride, but other than that, we just hitchhike," she told the driver. The couple gets by on his disability payments and on donated food from food banks. Neither has a cellphone. When hitchhiking, Mr. Coombes says he protects himself by carrying a club or a screwdriver.

British Columbia is infamous for serial killers and criminals who often targeted aboriginal women. In 2007, Robert William Pickton, a pig farmer, was convicted of killing six women, though the DNA or remains of 33 women were discovered on his land. Many of them were aboriginal. One of Canada's youngest serial killers, Cody Legebokoff, was 24 when he was convicted in 2014 of killing four women near the Highway of Tears. David Ramsay, a former Prince George provincial court judge and convicted pedophile, was imprisoned in 2004 for sexually and physically assaulting indigenous girls as young as 12.

Anguished family members said they received little help from the authorities, a sharp contrast to the cases of missing white women. After Ms. Chipman vanished in 2005, her aunt, Ms. Radek, said the police objected to the family putting up its own missing posters. "They knew we were searching day and night, and they did nothing to help us," she said. The next day, she said, a white woman disappeared near Vancouver "and the police were out in the streets putting up posters."

After her daughter Ramona disappeared in 1994, the police refused to act, said Matilda Wilson, a member of the Gitxsan First Nation. "They gave us all these different excuses that she might be back tomorrow or next week," Ms. Wilson said. "There was no hurry or alarm about it, so we started looking ourselves."

Despite multiple searches, Ms. Wilson, a single mother of six who is now 65, said there was no sign of Ramona until she had been gone for seven months, when Ms. Wilson received an anonymous phone call telling her that the girl's body was near the airport. Police officers searched the area but found nothing, she said. In April 1995, two men riding all-terrain vehicles by the airport discovered Ramona's remains buried under some trees. Plastic flowers and a glass cross now decorate her grave in a Smithers cemetery, a few blocks from Ms. Wilson's tidy trailer-park home.

Angry with the police for failing to find the teenager or to alert people to the history of missing women near Highway 16, Ms. Wilson and her family organized a memorial walk in June 1995 that has become an annual event, garnering attention from the news media and inspiring activism from families of other missing women.

"We want closure, and we're not going to give up," Ms. Wilson said as she swept leaves from her daughter's gravestone.

One recent afternoon, three young aboriginal sisters and their female cousin were walking across the Moricetown Indian Reserve, which abuts the highway. Asked about the Highway of Tears, one of the women, Rochelle Joseph, an unemployed 21-year-old, said the sisters never hitchhiked because they grew up hearing about the victims, including their cousin, Ms. Chipman.

Still, the menace of the highway haunts their lives.

"The stories made us cautious," Ms. Joseph said quietly, voicing their fear of a serial killer lurking behind the steering wheel of any strange car. "He's probably still out there."