[QUOTE=DSYoungEsq]
Ok, I’m going to make one last post in this increasingly silly thread.
This is directed directly at Wee Bairn.
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You are not actually asking if they are legal; you are wanting to assert that they should not be legal, in other words, you wish to debate the situation, because you don’t like them.
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They are legal. You’ve been answered this. They are legal because:
a. There is no specific law that prohibits the use of them, and
b. There is no common law principle which would compensate you as the owner of a vehicle who drives over them, so long as they are not negligently installed.
I understand that you do not LIKE this answer, but it is the answer to your question. If you wish to debate the morality or sensibility of allowing them to be used, I suggest opening a thread in Great Debates or In My Humble Opinion.
As for other options, what options would you prefer? The spikes exist in places where cars must be allowed ingress; they exist to prevent unauthorized egress. A barrier, such as a wall or fence would preclude ingress. A gate may be able to regulate ingress and act as a deterrent for some to egress, but there are many who would blithely drive through a gate arm to avoid a large parking fee. Those people are going to think twice about driving over spikes.
[/QUOTE]
How abut a six foot gate, that opens and closes by remote control. Most apartment complexes I have seen utilize these to achieve samer puporse.
No one here has cited regulations that they are absolutely legal in the one particular scenario I encountered- one small sign. The statutes quoted, if in effect everywhere in the US, there would be debate if it constituted adequate warning. My point is, in the scenario I personally encountered, I would argue adequate warning was not present.
I have seen People’s Court cases where someone argued and won (I know, I know citing People’s Court) brcasue a no parking sign was viewed as adequate (small, faded and confusing IIRC). Maybe other setups of these in other towns are blatantly obvious. But consider the fact that my experience and exposure to this may not be the same with those in other citites and countries. Maybe if some of you saw the one I saw, you would say “I agree, this one is not like the ones I see, it is not marked enough”. 
And I get out and travel fairly often, live in a fairly large city, but have seen these once in my life- in an airport parking lot. I do not frequent public parking lots often, but have never even seen them when driving by them.
IOW, if these are legal, I think in my particular case, it could possibly be argued and won based on not being marked well enough.