Construction costs are currently skyrocketing

I see prices from around €2.5 per linear meter for Douglas fir at regional timber dealers up to around €6 for, for example, thermo-pine, and up to around €7 per linear meter for Siberian larch (A-grade, 27x134mm, smooth/ribbed). Rounded up on the high end by tropical wood from €9 to €17, everything is possible.

Wow, that is significantly cheaper than what I see here. The cheapest was Douglas fir for €5.99.

What wood would you recommend if I don't want tropical wood and smooth boards without ribbing?

I'm not a wood expert and can't tell you anything about slipping, but larch, oak, and robinia are usually recommended as durable alternatives to tropical wood.

So much opinion with so little knowledge. May I conclude from your opinion that the higher the speed, the safer you are on the road? Brilliant, you deserve the Nobel Prize. If you have never heard of it, please google reaction distance, braking distance, and momentum.

I do not discuss on that level.

2.5€ per running meter for Douglas fir up to about 6€ for e.g. Thermo pine up to about 7€ per running meter for Siberian larch (A-quality, 27x134mm, smooth/ribbed).

I only know the Bauhaus prices from 2017; back then I paid 8.99 for Douglas fir 3000x140x24, wood of very good quality. I used it to build a 5m bench and 2 raised beds. In 2021 I bought the same wood for 12.99, but with many knots etc.

I do not discuss at that level.

I just lose my temper when I read: 170 km/h or even faster is no more dangerous than 120 or 130 km/h. How does one come to such an assessment? Let's just assume the number of accidents is the same at 200 km/h as it is at 130 km/h, physics says it simply hurts more the faster you go. Longer reaction distance = faster impact. Longer braking distance = faster impact. Higher speed = harder to catch. Higher speed = harder to avoid. Higher differential speed = higher accident potential. And no matter what some claim, the faster you go, the higher the fuel consumption.

I simply lose my temper when I read:
170km/h or even faster is not more dangerous than 120 or 130km/h.

Of course, the risk of injury is higher.

Years ago, there was a report in the ADAC, which questioned why fewer people die in traffic in Germany than in the USA.

Roughly, the conclusion was that vehicles are better maintained technically and driving practice and training are better.
And what really surprised me back then was that drivers are used to higher speeds and therefore drive more safely when they are going slower.