The summary says:

The evidence shows the risk of having a crash is increased both for vehicles traveling slower than the average speed, and for those traveling above the average speed. The risk of being injured increases exponentially with speeds much faster than the median speed. The severity / lethality of a crash depends on the vehicle speed change at impact. There is limited evidence suggesting lower speed limits result in lower speeds on a system-wide basis. Most crashes related to speed involve speed too fast for the conditions. More research is needed to determine the effectiveness of traffic calming.In the U.S. in 2018, 9,378 people were killed in motor vehicle crashes involving at least one speeding driver, which accounted for 26% of all traffic-related deaths for the year.In Michigan in 2019, excessive speed was a factor in 18.8% of the fatalities that resulted from fatal motor vehicle crashes and in 15.6% of the suspected serious injuries resulting from crashes.The Road and Traffic Authority (RTA) of the Australian state of New South Wales (NSW) asserts speeding (traveling too fast for the prevailing conditions or above the posted speed limit) is a factor in about 40 percent of road deaths. The RTA also say speeding increases the risk of a crash and its severity.
Youth
Insurance statistics demonstrate a notably higher incidence of collisions and fatalities among drivers aged in their teens or early twenties, with insurance rates reflecting this data. These drivers have the highest incidence of both collisions and fatalities among all driver age groups, a fact that was observed well before the advent of mobile phones.Females in this age group exhibit somewhat lower collision and fatality rates than males but still register well above the median for drivers of all ages. Also within this group, the highest collision incidence rate occurs within the first year of licensed driving. For this reason, many US states have enacted a zero-tolerance policy wherein receiving a moving violation within the first six months to one year of obtaining a license results in automatic license suspension. South Dakota is the only state that allows fourteen year-olds to obtain drivers licenses. Old age
Old age, with some jurisdictions requiring driver retesting for reaction speed and eyesight after a certain age. Sleep deprivationVarious factors such as fatigue or sleep deprivation might increase the risk, or numbers of hours driving might increase the risk of an incident. 41% of drivers self report having fallen asleep at the wheel. : 41  It is estimated that 15% of fatal crashes involve drowsiness (10% of day time crashes, and 24% of night time crashes). Work factors can increase the risk of drowsy driving such as long or irregular hours or driving at night. Drug use
Including some prescription drugs, over the counter drugs (notably antihistamines, opioids and muscarinic antagonists), and illegal drugs.