Well, what about if the bushes were made of legos or plasticine? Or perhaps a candy mountain?
Now, if you want to arrive to actual figures about the size of runoff areas, you have to use the envelope of trajectories and a friction factor.
G-G diagram, basis of possible trajectories, Charlie
I suppose I'm "ruining" discussions based on opinions, because, sadly, in engineering you HAVE to measure things and arrive to properly designed objects: you know, wishful thinking is not the base of design.
That's why we have to have a certificate to be able to design, like doctors need one to operate: people's lives depend on your ability.
Original ideas are not allowed, original
work it is.
So, if you actually measure the friction factor of twigs and arrive to a solution that proves that cars will stop before they hit something or somebody, be my guest.
Once you do that you have to show the owner of the track that your solution is cost efficient and spectators are not located one mile away from the track because that's the distance cars need to be stopped.
That's why leca or gravel is not used anymore.
In case someone is interested on why paved runoff areas are used, well, why don't you read the experts? It must be the fourth time I post the following text, copying and pasting:
I don't see why asphalt runoffs are a matter of opinion. They are necessary.
The fact is that leca (gravel) traps are dangerous.
"
Gravel traps on road racing courses should be paved over so drivers can steer, brake and recover" -- John Fitch --
Now, if you know a little about barriers, you know who Mr. Fitch is and then you agree with him. If you don't know who he is, perhaps you can find very quickly.
Jhon Fitch in the 60's before receiving the Kenneth Stonex Award from the Transportation Research Board, National Academy of Sciences, for his lifelong contributions in the field of roadside safety
Now, from a really old TRB magazine, I find this (which I've already posted five years ago, pardon me for being so insistent):
"
The entire series of tests on gravel traps indicate a deceleration of only 0.5 G, or the rate of moderate braking for a passenger car.
The full scale study determined that even this modest rate does not begin until the car has slowed to 50 mph. This compares to a 3 to 4 G braking capability for Formula One cars on a paved surface. Then there are the lesser problems of cars being eliminated from races due to damage caused by the gravel, or by simply getting stuck."
Transportation Research Record 1233, 1989, Design and Testing of Roadside Safety Devices
1989. It's not exactly yesterday's news.
So, if you wish to decelerate mildly (and wildly) a car, use a gravel trap.
Is that or invention a new barrier: it's probably easy to do, why should we waste time with expensive tests and fancy university professors?