At high speeds a driver can’t do anything if they see an obstruction. Breaking distances on trains tend to be measured in miles, not metres.

Australia uses what are called road trains, which essentially is 3 full sized semi-trailer loads pulled by a massive single cab travelling 90km/h. A good place to find them are the highways between Adelaide and Perth or Adelaide and Darwin. At night, their stopping distance is greater than their headlights can reach; if they see something, it is too late to stop and the choice is swerving and likely tipping or plowing on through. This is why they have bull bars on the front (you might know them as cow catchers), so when there is a herd of cows on the road staring you down the cab can plow straight through without slowing.

(or maybe tech has caught up in the last few decades and they detect obstructions from further away, but that would spoil the story)

Tech would have needed to see through terrain (road is not always flat - even though sometimes the crests and dips are so rare there's a warning sign ahead: https://media.gettyimages.com/videos/outback-road-sign-of-cr... )...and be retrofitted into the existing cabs. So, no: the tool of choice is still brute force, literally.

Sensors would work. If the cab isn't already tall enough (they are big!), you could mount the sensors on a pole. The road isn't always flat, but flat enough; I doubt a road train can deal with much of a gradient.

They could carry a set of battery packs on the roof and a pair of drones acting as scouts, one flying ahead with cameras and lidar for 10 minutes while the other one returns to swap out its battery.

Cool...but you need three to have backup, and a battery swap mechanism, and a charging system, and this contraption happens to be more complex than the rest of the car combined. I mean, it could work...but it feels very Inspector Gadget-ish.

What happens if there's a broken car/truck blocking the road?

The same thing that happens when any road vehicle meets a break down they didn't see in time, except the massive truck is more likely to win.

http://divine.vic.gov.au/lifestyle/health-and-wellbeing/road... has an account of a collision with a road train:

"The road train driver had slowed down to make a left-hand turn at a crossroads and Scotty had slammed into him at over 100 kilometres an hour. According to the autopsy, Scotty was over the legal alcohol limit. The driver of the road train kept going once he had completed the corner. I was later told he thought he felt a shift in the load as he slowed the vehicle to negotiate the corner."

Anyone wanting to make autonomous trucks perfect should remember the bar is actually pretty low...

Braking to a stop is the best option (which is not always available, yes). Emergency braking to half the speed is the difference between "8 fatalities" and "hundreds of fatalities"; Ek=mv^2 - note that velocity squared*.

Case in point: https://en.wikipedia.org/wiki/2008_Stud%C3%A9nka_train_wreck - train hits bridge at 90 kph instead of 135 kph; a 2/3 speed, but less than 1/2 the kinetic energy.

They can, however, hit the brakes as best they can (kinetic energy is proportional to the square of velocity, so this helps a lot), and warn passengers to brace for impact (example: https://en.m.wikipedia.org/wiki/Glenbrook_rail_accident#Effe...)

I agree drivers have other benefits. I will say, you made me realize that an electric sled with 3D LIDAR could check our track hundreds or thousands of meters in front of the train and confirm the track was still safe.