Are there such things as tranquilizer darts for humans.... something safe? Or is that the problem?

No. I'll put it you like this- the people who use drugs to put people to sleep- anesthesiologists- study for years to do this, they do it in a controlled environment in the operating theatre,and the drug mix and dose has to be personally tailored to the patient based on their medical history, physical exam, lab tests, etc, AND they constantly monitor the patient's vital signs throughout the operation. If there was a drug that could simply reliably put people to sleep safely with a single injection, do you honestly think they would be doing all this?

Sleep drugs are basically nothing like you see in the movies- there is no such thing as a special dart that will safely and reliably put anyone you hit with it to sleep. It has to be tailored to the individual person- for instance, if you got the dose required to disable a massive, drugged-up bodybuilder and gave it to a tiny young woman with a health problem, you would probably kill her several times over. Also, a dart will usually hit muscle rather than a vein, and it can take quite a while for drugs given there to do anything- potentially a few minutes at a minimum (anaesthesiologists give their drugs into a vein where the response is a few seconds. You can give sedative drugs into a muscle in the hospital for a violent patient but even that requires constant monitoring and observation).

Basically, there are no drugs or darts that would be effective for this. There are tasers but they need to be fairly close-range and they can fail- I once say the police shoot a taser into a drugged-out guy on PCP to basically zero effect (this may also have been due to the prongs landing too close together and the charge not spreading out enough to have any effect). Spray can work at close range as well.

In the Dallas situation, keep in mind that this was an ex-military guy sniping at the police from cover at range, so a lot of less-than-lethal options would not have been a realistic option for the police in that situation.

No, not useful against humans. How much drug do they need in the dart? It varies person to person ... the dose that might make one person a little drowsy might put another person into a life threatening overdose. Besides, these drug don't work right away ... in a life and death situation, you can't wait around after taking your shot hoping the drug will take effect.

In a situation like what unfolding in Dallas, the shooter needed to be neutralized. Tear gas doesn't do that. Pepper spray doesn't do that. Can't get close enough to deploy a taser.

A trank would work But its the distance thats the problem,they have and extremely low accuracy, 100 feet or so.Which does no good in a senerio where a target is never that close,A pistol is accurate up to 75 to 100 yards a rifle A 500 to 1000 yards A 308 or a good sniper rifle , A mile,

Darts ahve to be aimed perfectly. Like by a trained military sniper. The drugs can be very dangerous, often causing death to many and do not work, especially on those who already used downers, well with many.

Weight has to be estimated and the dosage measure.

Aiming well and dosage cannot be done on the fly when someone is attacking you or others.

Cosp shooting at an attacker rarely hit and actual death is very rare when the bad guy is hit.

One of the basic cop rules is than if you have to use your gun you shoot to kill, not to disable. Using the robot to deliver an explosive was a brilliant way to take out someone who can't be reached with a firearm.

those things are too slow to be effective, the police talked to this criminal for hours and he was never going to give up.

I don't see a problem with killing him rather than risking more lives.

You don't take tranquilizer darts to a gun fight.

Tranquilizing agents don't affect everyone uniformly.

I think tazers do the job for humans