delivered the Opinion of the Court.
¶1 Dakota Fire Insurance Company filed a declaratory judgment action in the United States District Court for the District of Montana to determine its duties under a policy of automobile liability insurance. Following submission of cross-motions for summary judgment, the United States District Court certified three questions to this Court for resolution under Montana law.
¶2 Pursuant to Rule 44, M.R.App.P, we accepted certification of the following three questions from the United States District Court:
1. Whether, under Montana law, an insured who pays separate premiums for uninsured and underinsured motorist coverage may recover both types of benefits under the terms of the insured’s policy if the insured was injured as a result of the negligence of an uninsured motorist.
2. Whether, under Montana law, an insured who pays separate premiums for uninsured and underinsured motorists coverage may recover, without offset, both types of benefits under the terms of the insured’s policy.
3. (a) Whether, under Montana Code Ann. § 33-23-203 an insured who pays separate premiums for uninsured motorist coverage for each vehicle insured under the policy, may stack the uninsured motorist coverage available for each motor vehicle listed within the policy, (b) If stacking uninsured motorist coverages paid for by separate premiums is prohibited by § 33-23-203, whether that prohibition is void as against public policy.
¶3 For the reasons set forth below, we answer question number 1 “No,” we need not address question number 2, and we answer question number 3(a) “Yes.”
¶4 The following statement of facts is as set forth in the Certification of Questions of Law issued by the United States District Court:
1. Plaintiff Dakota Fire Insurance Company is incorporated under the laws of North Dakota and is a citizen and resident of that State.
2. Defendants are individuals residing in Missoula, Montana, and are each citizens of that State.
3. Plaintiff Dakota Fire Insurance Company issued to Defendants Warren Oie and Diana Oie a policy of motor vehicle liability *489 insurance, including uninsured motorist coverage and underinsured motorist coverage, under policy number 13C-80-56 with a coverage period commencing April 23,1992, and ending October 23, 1992. A true and correct copy of the policy ... is attached hereto as Exhibit “A” and incorporated herein by reference. The policy insures two vehicles. The policy contains two separate amendatory endorsements for uninsured motorist coverage and for underinsured motorist coverage, in the amount of $500,000 each. The Oies paid separate premiums, for each of their two insured vehicles, for uninsured and for underinsured motorist coverages. Accordingly, a total of four separate premiums were charged for the uninsured and underinsured motorist endorsements.
4. On September 5,1992, Defendants were riding in a 1986 Ford Aerostar van, driven by Defendant Diana Oie. Defendants were traveling northbound on U. S. Highway 93 near Florence, Montana. A 1987 Mercury Topaz driven by Tori Jo Larson was southbound on U.S. Highway 93 and stopped at the intersection of White Cloud Lane, preparing to make a left turn. A1987 Ford pickup driven by Carol Morris failed to stop and struck the Larson vehicle. The Morris vehicle was owned by Kevin Currieri, who had not purchased any insurance for the vehicle. The Morris vehicle then spun into the north-bound lane and was struck by the Oie vehicle. Diana Oie’s daughter, Amanda Sue Moore, was fatally injured. The Oies’ son, Defendant Jeffrey Oie, sustained serious head and facial injuries. Defendant Warren Oie sustained back injuries. Other injuries, physical and psychological, are disputed and are being separately litigated in Federal District Court, Missoula Division.
5. Plaintiff contends the only coverage available is one uninsured motorist coverage in the amount of $500,000.
6. Defendants contend they may stack the uninsured motorist coverage limits for the two vehicles insured under the policy for an aggregate uninsured motorist coverage limit of $1,000,000. Plaintiff contends that Mont. Code Ann. § 33-23-203 precludes intrapolicy stacking of uninsured motorist coverage limits, even when separate premiums are paid for each automobile insured under the policy.
7. Defendants contend that if the amounts they are legally entitled to recover as damages exceed the uninsured motorist coverage limits, they may then recover pursuant to their underinsured mo *490 torist endorsement for which they paid a separate premium. Plaintiff contends the two coverages are mutually exclusive.
8. Defendants contend they may also stack the underinsured motorist coverage limits for the two vehicles insured under the policy for an aggregate underinsured motorist coverage limit of $1,000,000. Plaintiff contends that Mont. Code Ann. § 33-23-203 precludes intrapolicy stacking of underinsured motorist coverage limits, even when separate premiums are paid for each automobile insured under the policy.
9. Plaintiff contends that if Defendants’ underinsured motorist coverage applies above and beyond their own uninsured motorist coverage, Plaintiff may offset sums paid pursuant to the uninsured motorist coverage from policy limits available pursuant to the underinsured motorist endorsement. Defendants contend the offset provision is void as against public policy. [Footnote omitted.]
DISCUSSION
¶5 1. Whether, under Montana law, an insured who pays separate premiums for uninsured and underinsured motorist coverage may recover both types of benefits under the terms of the insured’s policy if the insured was injured as a result of the negligence of an uninsured motorist.
The policy of insurance issued in this matter provides separate, distinct coverages to the insured for liability, medical payments, uninsured motorist, and underinsured motorist claims. Those policy terms must be interpreted according to their “usual, common sense meaning as viewed from the perspective of a reasonable consumer of insurance products,” which determines the rights and obligations of the parties.
Stutzman v. Safeco Ins. Co. of America
(1997),
¶6 As indicated on the declarations page of the policy, the insureds paid separately computed premiums for the uninsured motorist and underinsured motorist coverages. The uninsured motorist coverage provides that the insurer
will pay compensatory damages which an “insured” is legally entitled to recover from the owner or operator of an “uninsured motor vehicle” because of “bodily injury”
1. Sustained by an “insured;” and
2. Caused by an accident.
*491 ¶7 The uninsured motorist coverage defines an “uninsured motor vehicle” as “a land motor vehicle or trailer of any type: 1. To which no bodily injury liability bond or policy applies at the time of the accident.”
¶8 The separate underinsured motorists coverage provides that the insurer
will pay compensatory damages which an “insured” is legally entitled to recover from the owner or operator of an “underinsured motor vehicle” because of “bodily injury:”
1. Sustained by an “insured;” and
2. Caused by an accident.
¶9 The underinsured motorist coverage (as modified by the amendatory endorsement) defines an “underinsured motor vehicle” as
a land motor vehicle or trailer of any type to which a bodily injury liability bond or policy applies at the time of the accident but the amount paid for “bodily injury” under that bond or policy to an “insured” is not enough to pay the full amount the “insured” is legally entitled to recover as damages.
¶ 10 Unlike the uninsured motorist coverage, the underinsured motorist coverage is subject to the additional limitation that the insurer “will pay under the coverage only after the limits of liability under any applicable bodily injury liability bonds or policies have been exhausted by payment of judgments or settlements.”
¶11 The Oies contend that they are entitled to collect both uninsured and underinsured motorist coverage and that the vehicle that caused the accident was both an “uninsured motor vehicle” and an “underinsured motor vehicle,” as defined by the policy, at the time of the accident.
¶ 12 Under the terms of the policy, a vehicle is “underinsured” only if it is the subject of a “bodily injury liability bond or policy” but the amount paid under that bond or policy is not enough to pay the full amount the insured is legally entitled to recover. The Oies contend that the requirement that there be coverage under a bond or policy is satisfied by the fact that the vehicle was covered by their own uninsured motorist coverage and that coverage was insufficient to pay the full amount that the Oies were legally entitled to recover. In other words, the Oies’ uninsured motorist coverage is a substitute for the uninsured tortfeasor’s missing liability insurance.
*492
¶13 The Oies rely on language from
Farmer’s Alliance Mut. Ins. Co. v. Miller
(9th Cir. 1989),
Companies selling auto insurance in Montana must offer uninsured motorist coverage. The Montana Supreme Court has interpreted this provision as expressing the legislature’s intent that uninsured motorist coverage serve as a surrogate for an uninsured tortfeasor’s missing liability insurance.... Uninsured motorist coverage acts as a substitute for a tortfeasor’s missing liability coverage.
Miller,
¶14 Based on this language from Miller, the Oies conclude that “if the policyholder has purchased UM coverage, the uninsured tortfeasor has liability insurance purchased for him by the policyholder.” Dakota Fire Insurance argues that when the above language is read in context of the balance of the court’s opinion, it is clear that the inadequate liability insurance that triggers underinsured motorist coverage is not the insured’s own uninsured motorist coverage, but the tortfeasor’s deficient coverage. In Miller, the Ninth Circuit went on to state:
Underinsured motorist coverage presupposes some liability insurance but acts as a gap-filler, ensuring that the insured recovers at least the amount he is insured for, even if the tortfeasor’s insurance coverage is deficient. By its nature, therefore, underinsured motorist coverage assumes the existence of some compensation from another source, namely the tortfeasor’s liability insurance.
Miller,
*493
¶15 We agree with Dakota Fire’s interpretation of
Miller.
Underinsured motorist coverage assumes that the tortfeasor carries liability insurance. This definitional prerequisite is not satisfied through substitution of the Oies’ uninsured motorist coverage. This interpretation is consistent with our holding in
Dagel v. Farmers Ins.
(1995),
In this case there was no other bodily injury liability policy in effect that applied to Dagel’s injuries because the driver of the other vehicle was uninsured. In interpreting insurance contracts, the words of the policy are to be understood in their usual meaning; common sense controls.
The Farmers’ policy defines an “uninsured motor vehicle” as one which is “not insured by a bodily injury liability bond or policy at the time of the accident.” Accordingly, under Farmers’ own definition, since the vehicle that injured Dagel was uninsured, there was no bodily injury liability bond or policy applicable to Dagel’s injuries at the time of the accident.
Dagel,
¶ 16 Although the present case involves underinsurance rather than an exhaustion requirement in uninsurance, the principles of
Dagel
still pertain. In the present case, the Oies, in order to establish that the tortfeasor was “under” insured, must first establish that he was “insured.” The Oies argue that the tortfeasor was vicariously insured by virtue of the Oies’ uninsured motorist coverage. The Oies attempt to distinguish
Dagel
by pointing out that in
Dagel,
the uninsured coverage was that of the car dealer, not the injured party. That, however, is a distinction without a difference. Regardless of whether the uninsured coverage derives from the injured party or a third party, the question is the same: Does the uninsured motor vehicle coverage
*494
serve as substitute liability policy for the non-insured tortfeasor? In
Dagel
we held that uninsured motorist coverage does not serve as a substitute liability policy for the tortfeasor that has to be exhausted by the injured party.
Dagel,
¶17 The Hawaii Supreme Court addressed this issue in
National Union Fire Ins. v. Ferreira
(Haw. 1990),
¶ 18 As here, the insured in
Ferreira
argued that her own uninsured motorist coverage satisfied the requirement of “liability insurance” on behalf of the tortfeasor. The court rej ected this argument and held that the insured was not entitled to collect both types of coverage.
Ferreira,
¶19 Although Montana has no statutory definition of “underinsured motor vehicle,” the policy in question, like the Hawaii statute, re *495 quires that the tortfeasor’s vehicle be covered by a bodily injury liability policy. Accordingly, we agree with the reasoning of the Hawaii court.
¶20 A motorist who carries both uninsured and underinsured motor vehicle coverage has two distinct and mutually exclusive coverages. If that insured motorist is injured by another motorist, the first determination is whether the tortfeasor is covered by bodily injury liability insurance. If he has no liability coverage, then he is not insured and the injured party may collect only on his “uninsured motor vehicle” coverage. Since the tortfeasor cannot be both uninsured and underinsured, the injured party may not invoke both types of coverage.
¶21 2. Whether, under Montana law, an insured who pays separate premiums for uninsured and underinsured motorists coverage may recover, without offset, both types of benefits under the terms of the insured’s policy.
¶22 Having held that an insured who pays separate premiums for uninsured and underinsured motorist coverage may not recover both types of benefits, we need not address the question of whether he or she may do so without offset.
¶23 3. Whether, under § 33-23-203, MCA (1991), an insured who pays separate premiums for uninsured motorist coverage for each vehicle insured under the policy, may stack the uninsured motorist coverage available for each motor vehicle listed within the policy. If stacking uninsured motorist coverages paid for by separate premiums is prohibited by § 33-23-203, MCA (1991), whether that prohibition is void as against public policy.
¶24 We are again confronted with the issue of whether insurance coverages may be stacked. This issue has arisen in a number of different contrasting contexts: uninsurance or underinsurance; named insured or occupant; interpreting policy language or statutory language; single policy or multiple policies. The present case presents the narrow issue of whether § 33-23-203, MCA (1991), precludes a named insured from stacking uninsured motorist coverages when the insured has paid multiple and separate premiums for such coverages.
¶25 In Sayers
v. Safeco Ins. Co. of America
(1981),
¶26 In 1995 we addressed a stacking issue presented in the context of a passenger asserting a claim against multiple policies rather than a single policy.
Chilberg v. Rose
(1995),
¶27 In
Farmers Alliance Mut. Ins. Co. v. Holeman
(1996),
¶28 First of all, the statement about
Sayers
was, as Dakota Fire concedes,
dictum
since the certified question before the Court in
Holeman I
pertained only to optional coverage for underinsured motorists, and did not encompass uninsured motorists coverage, which is mandatory and specifically referenced in the statute, § 33-23-203, MCA (1995). Secondly, our characterization of § 33-23-203, MCA (1995), in
Holeman I
merely restated the statutory language that the stacking of uninsured motorist coverage is disallowed regardless of the number of
vehicles
insured.
Holeman
I,
¶29 In interpreting the statute in
Holeman I,
we noted that § 33-23-203, MCA (1995), only addressed mandatory coverage. “The question of whether excess or additional coverages, such as underinsurance coverage, can be stacked was left as a matter of policy interpretation.”
Holeman I,
*498
¶30 In
Bennett v. State Farm Mut. Auto Ins. Co.
(1993),
Montana citizens should have a reasonable expectation that when they purchase separate policies for underinsured motorist coverage, they will receive adequate compensation for losses caused by an underinsured motorist, up to the aggregate limits of the policies they have purchased.
Bennett,
¶31 The present case involves only one policy as opposed to the two policy situation in Bennett. That, however, is a distinction without a difference. The point is that Dakota, like State Farm in the Bennett case, received separate premiums (valuable consideration) for separate coverages. In contrast with the passenger in Holeman II, the Oies have standing to argue “reasonable expectations” because they are named insureds who paid premiums.
¶32 In the present case we must determine whether, under § 33-23-203, MCA (1991), the Oies, who paid separate premiums for uninsured motorist coverage for each vehicle insured under their policy, may stack the uninsured motorist coverages. For some 25 years, this Court has recognized the strong public policy in favor of enforcing coverage for which the insurer has received valuable consideration, to give the insured the benefit of his or her bargain.
Ruckdaschel v. State Farm
(1997),
¶33 Section 33-23-203, MCA (1991), provided as follows:
Unless a motor vehicle liability policy specifically provides otherwise, the limits of insurance coverage available under any such policy, including the limits of liability under uninsured motorist coverage, must be determined as follows, regardless of the number of motor vehicles insured under the policy:
(a) the limit of insurance coverage available for any one accident is the limit specified for the motor vehicle involved in the accident;
(c) the limits of coverage specified for each motor vehicle insured under the policy may not be added together to determine the limit of insurance coverage available under the policy for any one accident.
¶34 We conclude that § 33-23-203, MCA (1991), superseded neither the public policy nor the insureds’ reasonable expectations. Unlike the 1997 version of the statute, the 1991 version applicable here makes no reference to the number of premiums paid. Rather, it focuses entirely on the number of vehicles insured and the “coverage specified for each motor vehicle.” Thus, although the statute initially references uninsured motorist coverage, the balance of the statute is not in accord with the principles of uninsured motorist coverage or the grounds for stacking of uninsured motorist coverage that we have previously upheld. First of all, in focusing solely on the vehicles covered, the statute ignores the fact that uninsured motorist coverage is personal to the insured, and that it is not dependent upon occupancy of a vehicle.
See Chafee,
¶35 The legislature, in adopting statutes, establishes the law of the state. Art. V, Sec. 1, Mont. Const. Our job is to construe statutes as written. “[T]he office of the judge is simply to ascertain and declare what is in terms or in substance contained therein, not to insert what has been omitted or to omit what has been inserted.” Section 1-2-101, MCA. We cannot construe the “regardless of the number of motor vehicles” language in § 33-23-203, MCA (1991), as defeating coverage for which the insured has paid multiple premiums and the insurer has received valuable consideration. A statute that focuses solely on vehicles insured does not have the effect of relieving an insurer from paying uninsured motorist benefits under each coverage for which it has received valuable consideration in the form of premiums. Had the legislature meant, as a matter of public policy, to preclude stacking of uninsured motorist coverages despite the insureds having paid separate premiums for such coverages, then it would have expressly said “regardless of the number of premiums paid.”
¶36 We hold that § 33-23-203, MCA (1991), does not apply in situations where an insured has paid separate premiums for uninsured motorist coverage. Accordingly, we answer question number three in the affirmative. Under § 33-23-203, MCA (1991), an insured who pays separate premiums for uninsured motorist coverage may stack the uninsured motorist coverages available within the policy.
