The World Health Organization's new global survey of road safety reports that 13,463 Kenyans died last year in crashes on the country's roads -- a toll more than four times higher than the government's figure of 2,965 deaths.
The rate of road traffic deaths in Kenya far exceeds the global rate and is somewhat higher than the average for Africa, WHO notes.
Kenya's road traffic fatality rate in 2017 stood at 27.8 persons per 100,000 population, according to WHO's calculations.
The global rate was 18.2 deaths per 100,000 people, while the Africa average was 26.6 per 100,000.
The WHO's estimate of road traffic deaths in specific countries often differs from governments' statistics because the United Nations agency does not place a time limit on fatalities resulting from crashes.
"In the case of Kenya," explains Dr Nhan Tran, the WHO's leading expert on road safety, "the reported number (2,965) comes from the National Transport and Safety Authority, and the definition that is used is 'died at the scene of crash'."
"We know that many more deaths occur after the crash, in the hospital and sometimes many months after the crash," Dr Tran added in an email message to the Nation.
"So the main reason for the under-reporting of deaths in Kenya is due to the very narrow definition of a road traffic death that is used."
The WHO's own figures for road fatalities are based on data from each country's death registry. Numbers from that source are "generally more complete than police or health data alone", Dr Tran said.
Governments are not believed to be deliberately under-reporting road traffic deaths, he added.
Instead, "it is often the case that data systems are weak."
Sometimes, deaths resulting from road crashes are not reported to police and some fatalities of this type may not be recorded correctly, the WHO expert said.
"So it really is an issue of capacity and quality of data systems in countries. Most governments want to know how big the problem really is," Dr Tran said.
Asked to assess the effectiveness of Kenya's road-safety laws and enforcement, he noted that some regulations, such as motorcycle helmet requirements, do conform to best practices.
"Others, such as drink-driving laws, do not," Dr Tran observed.
Kenya's permissible blood-alcohol-content limit of 0.08 g/dl (grams per deciliter) is higher than the recommended limit of 0.05 g/dl, he noted.
"Another important challenge in Kenya is enforcement," Dr Tran wrote. "While laws are in place, they are not always enforced."
The WHO's new global survey finds that road traffic deaths continued to increase in 2017, reaching a total of about 1.35 million.
Road crashes are now the leading killer of children and young adults, the report states.
The risk of road traffic death remains three times higher in low-income countries than in high-income countries, with Europe accounting for the lowest rate among the world's regions -- 9.3 deaths per 100,000 population.
Africa's rate is the world's highest.
Pedestrians and cyclists are the victims in 44 percent of all fatal road crashes in Africa, compared to a global average of 26 percent for those types of road users, the report indicates.