Quoted:
Legal. I never once heard public transit being listed as a prohibited place, and there's no signage (at least as far as I can tell) that suggests you can't or will be fined/kicked off if you are.

76-10-1504. Bus hijacking -- Assault with intent to commit hijacking -- Use of a dangerous weapon or firearm -- Penalties.
(1) (a) A person is guilty of bus hijacking if the person seizes or exercises control, by force or violence or threat of force or violence, of a bus within the state.
(b) Bus hijacking is a first degree felony.

(2) (a) A person is guilty of assault with the intent to commit bus hijacking if the person intimidates, threatens, or commits assault or battery toward a driver, attendant, guard, or any other person in control of a bus so as to interfere with the performance of duties by the person.
(b) Assault with the intent to commit bus hijacking is a second degree felony.

(3) A person who, in the commission of assault with intent to commit bus hijacking, uses a dangerous weapon, as defined in Section 76-1-601, is guilty of a first degree felony.
(4) (a) A person who boards a bus with a concealed dangerous weapon or firearm upon his person or effects is guilty of a third degree felony.
(b) The prohibition of Subsection (4)(a) does not apply to:
(i) individuals listed in Subsections 76-10-523(1)(a), (b), (c), (d), and (e);
(ii) a person licensed to carry a concealed weapon; or
(iii) persons in possession of weapons or firearms with the consent of the owner of the bus or the owner's agent, or the lessee or bailee of the bus.