On another web page, the RTA qualify their claims by referring to one specific piece of research from 1997, and writes "research has shown that the risk of a crash causing death or injury increases rapidly, even with small increases above an appropriately set speed limit. "The contributory factor report in the official British road casualty statistics show for 2006, that "exceeding speed limit" was a contributory factor in 5% of all casualty crashes (14% of all fatal crashes), and "traveling too fast for conditions" was a contributory factor in 11% of all casualty crashes (18% of all fatal crashes).In France, in 2018, the speed limit was reduced from 90 km/h to 80 km/h on a large part of the local outside built-up area road network in the sole aim to reduce the number of road fatalities. Assured clear distance ahead
A common cause of collisions is driving faster than one can stop within their field of vision. Such practice is illegal and is particularly responsible for an increase of fatalities at night – when it occurs most. Driver impairment
Driver impairment describes factors that prevent the driver from driving at their normal level of skill. Common impairments include:

Alcohol
According to the Government of Canada, coroner reports from 2008 suggested almost 40% of fatally injured drivers consumed some quantity of alcohol before the collision. Physical impairment
Poor eyesight and/or physical impairment, with many jurisdictions setting simple sight tests and/or requiring appropriate vehicle modifications before being allowed to drive.
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.