On Oct. 20, the National Transportation Safety Board (NTSB) said, commercial truck and bus drivers should be screened for sleep apnea -- a disorder that's contributing to driver fatigue. 

The NTSB sent a letter to the Federal Motor Carrier Safety Administration recommending that medical examiners be required to question drivers about the disorder. In addition, the board recommended that programs be developed to better identify sleep apnea, the Associated Press reported. 

The NTSB also sent a similar letter to the Coast Guard, and has previously sent such recommendations to the Federal Aviation Administration and to local transit agencies across the nation. 

In the letters, NTSB Chairman Deborah Hersman stressed that sleep apnea denies drivers of the rest they need and has been found to be a factor in incidents involving every mode of transportation. Among the accidents cited in the letters was a Jan. 2008 crash that occurred when a bus took a curve too fast on a rural highway in Utah and careened down a mountainside. The bus was carrying people returning from a ski trip. The accident killed nine people and injured 43 others. The driver, who suffered from sleep apnea, had reportedly been having trouble using a breathing device for the disorder in the days before the crash. 

According to a 2002 study, 7 percent of adults have at least a moderate form of sleep apnea. Often, people are unaware they have the disorder because the condition goes undiagnosed. 

People with sleep apnea have pauses in breathing or shallow breaths while they sleep. Breathing pauses often occur five to 30 times or more an hour. Typically, normal breathing then starts again, sometimes with a loud snort or choking sound. They move out of deep sleep into light sleep when their breathing pauses or becomes shallow. The result is poor sleep quality that makes them tired the next day. Sleep apnea is one of the leading causes of excessive daytime sleepiness and a major contributor to driver fatigue.