This is still happening.

A workaround is to build sandbags behind to stop the truck before it rolls away.

Wow.. this is from 2023 and is still awaiting internal testing?

The video above shows the old spawning system, but the newer building mode has the same issue. In fact any editor mode has this issue, hence also GM.

I have not found a vehicle that would spawn without the hand brake on. Or has anyone followed a car that rolled away and went in to driver seat to check and then found that hand brake was off.

The reason why the car rolls away is that in most cars (and I have not found one in the game that would not follow this rule) the hand brake only works on one axle, usually the rear one (that is why hand brake turns are a thing) and in trucks with more axles the rear most one. And when a car is spawned, it is dropped to the ground and that means that it will bounce and while bouncing the tires are not making contact to the ground and therefore the brakes are not very effective at that time. And once the car/truck picks up a little momentum, braking with just one axle is not very effective.

This might be a case where the game is just too realistic for some people.

And I did check this myself on GM and when I watched the truck bounce and slide the rear most tires did not move indicating that the hand brake was engaged.

There is another matter that the normal brakes effectiveness depends on whether the car is on neutral or on drive gear which should not be the case.

I have not found a vehicle that would spawn without the hand brake on. Or has anyone followed a car that rolled away and went in to driver seat to check and then found that hand brake was off.

I double checked it in the workbench and you're correct that they do spawn with the handbrake on. I would argue that the issue is in fact how the handbrake behaves on neutral gear. When I use GM to drag a car to a slope with the handbrake on, it will not slide down when I put it on 1st gear, but it will when I put it on neutral. Ofc cars spawn in neutral, which leads to OP's issue. The ticket's title and description should be updated accordingly.

Edit: They also don't slide down when I put them in 1st gear without the handbrake on. Seems like the handbrake is too ineffective. I guess either the handbrake has to be improved or they should spawn in 1st gear.

We are getting quite far from the original posts point, so if this goes on much further a new ticket might be in order, but I'll say this here for now.

There are quite a few issues concerning the braking behavior. I would guess that most can be explained by the fact that this is not a driving simulator, so there is a number of physics shortcuts in use. I have mostly played in experimental recently, but as far I have checked the same issues exist in the main branch. And before getting into specifics I'd bet that the full assist driving mode is a major factor why many of these exist.

I use the semi assist driving mode, so take that into account, these should work in any car or truck, my latest tests were done with the Willys Jeep.

1. If you roll to a stop in neutral gear at an uphill incline, the car will roll backwards. If you tap the hand brake to stop the car, it will roll when you release the brake, but if you hold the hand brake long enough to hear the hand brake engaging sound and the character does the animation, the car will not roll when you release the hand brake button even though the hand brake does not stay on. The car will start to roll if you tap the throttle. So there seems to be a advanced hill hold system in all the cars even though that was not available in the 80s.

2. If you change in to neutral while going forward the car's brakes are less effective than in drive gear. The brakes are less effective also when you just turn the engine off while moving forward, but that would happen with modern systems, not sure with all the cars modeled in the game though.

There are more examples, but as I mentioned maybe a new ticket would be better.