Some comments, sorry for incoherences, I wrote all of this in a hurry:
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Fat Bloke: new Tilke circuits have the "astroturf" that you ask for, for the purpose you imagine: if you put a wheel out of the pavement, you lose the car and then, several seconds, but you can recover and continue. Check the outside of curve 8 in Turkey if you do not believe me: you'll find a thin strip of grass put there for that very purpose.
- Regarding
bogaTYR comments about Nürburgring, any hill or valley design includes,
necessarily, a calculation to ensure that a car can brake within the visibility range it has. Any other kind of design would be mad.
That's the way vertical curves have been designed since road were invented. Concave vertical curves ("valleys") have to be designed in the same way because at night your car lights do not illuminate the whole road.
So, AFAIK, there are no vertical curves without visibility in regular tracks. I concede that at Nürburgring, originally designed as a regular road, for regular cars at regular speeds, it could happen that you have vertical curves without visibility, and that could be the origin of bogaTYR comment,
but if you try to propose this kind of design today people would look at you in the same way as they would look a father giving his toddler a loaded gun.
Phil Hill flying over a vertical curve at Nürburgring: as bogaTYR explains, that's why you cannot race at this track today with F1 cars, the track is outdated for the speeds of the cars
You do a similar calculation for horizontal obstacles: you have to take in account the visibility the obstacle gives to the driver and design a curve with a degree of curvature that allows you to brake.
These distances include reaction time, as it is logical.
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You can use other things, if you want to separate good drivers from regular ones. For example, what I like to do (in the few designs I've made) is to use
longitudinal slopes in the entrance of the curves, to trick the driver, because braking distances are increased and oversteering in the exit is reduced.
I also like to design
spiral transition curves at the entrance and the exit of curves (like the ones at China) because they require a throttle control that it's kind of difficult to achieve. Besides, spiral curves allow you to increase side slope
in the transition curve, instead of increasing it in the straight.
You might have noticed at old roads with pure circular curves or at old tracks with the same kind of curves (like Catalunya)
that the transition of the sideslope happens in the straight.
Repsol (I think 
): the lonely spiral curve in Catalunya (the curve to the right). The rest are pure circular curves (including the entrance to Repsol, to the left).
If you haven't noticed, check how the driver moves the steering wheel at the next old road you travel.
Before the curve, in the straight, the driver will have to steer in the opposite sense of the next curve (if the next curve is to the right, he has to steer slightly to the left).
Why? Because in the straight there is a transition of the sideslope. Sorry if you already know this, but here there is a couple of graphics for those who don't (and who might learn something for the next time they walk a circuit before a race):
A straight. Notice that the edges are lower than the centerline, for water to run out. You, unconsciously, take in account this slight (2%) sideslope when driving
A regular curve: the red line shows the lower edge (because of the side slope) and the yellow one shows the upper edge.
A pure circular curve, like the ones at old roads and old tracks. Notice (sorry for the drawing) that the "higher" edge starts to "twist" before the entrance of the curve, in the straight. Sorry for the simplification: the lower edge also "goes down", because the curve normally has a sideslope larger than 2% (up to 10%)
That kind of "subtler" tricks you can expect from a road designer, but you'll never would design on purpose a zone of the road where an obstacle would give the driver no time to react, specially if it's a stopped car with a driver in it, a driver that might be unconscious.
) they might like this
