The optimists among us look at Google's self-driving cars and see a safer future, but the FBI would rather focus on their potential for death and destruction.

The US's Federal Bureau of Investigation has issued a restricted report, obtained by The Guardian with a public records request, warning of the dangers of self-driving cars - namely, that they don't have drivers.

Imagine a high-speed car chase without a human behind the wheel, the report suggests. Or, worse, imagine a driverless vehicle being used as a "lethal weapon."

But would the lack of a driver really make a difference in those situations?

Criminal multitasking

The report also notes that criminals in cars will be able to take their hands off the wheel and their eyes off the road when a car can drive itself.

This could be bad news during high-speed chases, when a perp might choose to put his hands on a gun instead.

The report, written by the FBI's Directorate of Intelligence's Strategic Issues Group, admits that autonomous cars will be more efficient and that "the risk [of] distraction or poor judgement leading to collision that stems from manual operation would be substantially reduced."

But it seems the Bureau is assuming criminals and terrorists will be able to override the safety mechanisms being built into self-driving vehicles, allowing them to speed through traffic lights and commit other offenses despite their programming.

It's not all bad

Despite the practical pessimism, the FBI also sees potential benefits for law enforcement, not limited to a possible reduction in traffic incidents involving first responders and police.

Driverless vehicles will be easier to tail, as well, and better at tailing other cars. They may be more efficient at three-point turns and other maneuvers that can slow responders down.

In other words, the FBI, like the rest of us, does see both the benefits and the potential for abuse of self-driving cars.

Interestingly the Bureau thinks Congress could legalize self-driving cars nationwide in the next five to seven years. Fingers crossed!