Laws about knives in vehicles
 

So last week me and a couple friends were driving home from a concert in Camden when I get stopped "for having my gps in the windshield". Long story short we all get searched and sent on our way, but my friend had a knife on him, that is shorter than his palm when opened. His dad is a NJ police officer, and he was told that a knife that size was legal to carry in a vehicle. But the cop that pulled us over (still in NJ, different county), said it was a felony to have in the car. Luckily he didn't arrest my friend for having it, but I was just curious what the actual law is, since I normally have a knife in the trunk of my car with my tools. Also I travel into PA frequently so I'd like to know the law there too, if possible.

New Jersey - Code of Criminal Justice

- 2C:39-3 Prohibited Weapons and Devices...

e. Certain weapons. Any person who knowingly has in his
possession any gravity knife, switchblade knife, dagger,
dirk, stiletto, billy, blackjack, metal knuckle, sandclub,
slingshot, cestus or similar leather band studded with
metal filings or razor blades imbedded in wood, ballistic
knife, without any explainable lawful purpose, is guilty
of a crime of the fourth degree.

- 2C:39-1 h. "Gravity knife" means any knife which has a
blade which is released from the handle or sheath thereof
by the force of gravity or the application of centrifugal
force... p. "Switchblade knife" means any knife or similar
device which has blade which opens automatically by hand
pressure applied to a button, spring or other device in
the handle of the knife... u. "Ballistic knife" means any
weapon or other device capable of lethal use and which can
propel a knife blade.

2C:39-6. f. Nothing in subsections b., c. and d. of N.J.S.2C:39-5
shall be construed to prevent... (2) A person carrying a firearm
or knife in the woods or fields or upon the waters of this State
for the purpose of hunting, target practice or fishing, provided
that the firearm or knife is legal and appropriate for hunting
or fishing purposes in this State and he has in his possession
a valid hunting license, or, with respect to fresh water fishing,
a valid fishing license;

(3) A person transporting any firearm or knife while traveling:
(a) Directly to or from any place for the purpose of hunting or
fishing, provided the person has in his possession a valid
hunting or fishing license; or

Pennsylvania - Pa. C.S.A. 18.908. Prohibited offensive
weapons. (a) Offense defined.--A person commits a
misdemeanor of the first degree if, except as authorized
by law, he makes, repairs, sells, or otherwise deals in,
uses, or possesses any offensive weapon. (b) Exception.--
It is a defense under this section for the defendant to
prove by a preponderance of evidence that he possessed of
dealt with the weapon solely as a curio or in a dramatic
performance, or that he possessed it briefly in
consequence of having found it or taken it from an
aggressor, or under circumstances similarly negativing any
intent or likelihood that the would be used unlawfully.
(c) Definition.--As used in this section "offensive
weapon" means... any... dagger, knife, razor or cutting
instrument, the blade of which is exposed in an automatic
way by switch, push-button, spring mechanism, or
otherwise.