This case concerns an application for a land development permit under Act 250, 10 V.S.A., ch. 151. The Pyramid Company (Pyramid) appealed from a decision of the district environmental commission denying its permit application for a shopping mall in the Town of Williston. Pyramid then appealed to the Chittenden Superior Court under 10 V.S.A. *298 § 6089(a). The matter is now before this Court pursuant to the superior court’s order certifying an interlocutory appeal under V.E.A.P. 5 (b). We hold that the trial court incorrectly granted permission for an interlocutory appeal, and therefore dismiss the appeal.
I.
In October of 1978, Pyramid obtained a building permit for the construction of a large shopping mall in the Town of Williston. Before commencing construction, however, it was necessary for Pyramid to obtain a permit under the provisions of Act 250. It is the struggle over that permit which is the basis of this case.
Intense opposition confronted the application. Four of the objections to this development form the basis of this appeal. First, the opponents argue that the permit should be denied because the mall would harm the economy of the City of Burlington. 1 Second, the mall would allegedly cause transportation problems extending beyond the Town of Williston. Third, the mall purportedly does not comply with the plan of the Town of Williston. Fourth, the proposed mall would violate 10 V.S.A. § 6086(a) (9) (H) because it is an excessively costly “scattered development.”
In an attempt .to disarm each of these objections, Pyramid filed a motion for partial summary judgment in the Chittenden Superior Court. In pertinent part, Pyramid contended: (1) economic impact to the City of Burlington is not cognizable under Act 250; (2) transportation congestion outside of the Town of Williston is beyond the scope of Act 250; (3) the Act 250 permit process does not permit further review of the proposed mall’s conformity with the plan of the Town of Williston; and (4) the proposal withstands scrutiny under the “scattered development” provision of Act 250 as a matter of law.
The trial court denied Pyramid’s motion for summary judgment. The court held that the economic impact of the mall on Burlington was cognizable under Act 250. The mall’s impact on transportation beyond the Town of Williston was *299 also held relevant to the permit process. The court concluded that Act 250 required a de novo determination on whether Pyramid’s application conformed with the Town of Willis-ton’s plan. Finally, the court held that more evidence would be required on whether the proposal violated the “scattered development” prohibition in Act 250.
Pyramid then moved for permission to take an interlocutory appeal to challenge the denial of summary judgment. Pyramid claimed that regardless of the existence of any material issues of fact, Pyramid was entitled to partial summary judgment as a matter of law on the questions proposed for certification. See V.R.C.P. 56, Reporter’s Notes (1971) (discussing the relationship of V.R.C.P. 56 to V.R.C.P. 12(b) (6)). The trial court certified five questions for review under V.R.A.P. 5(b):
(1) Does 10 V.S.A. § 6086(a)(7) authorize consideration of whether projected decline in shoppers goods sales and resultant lowering of property values and reductions in tax revenues and municipal services may constitute an unreasonable burden placed on the ability to provide municipal or governmental services of a municipality which is not contiguous to the municipality in which the proposed development is to be located?
(2) Does 10 V.S.A. § 6086(a)(5) authorize consideration of whether a proposed development will cause future unreasonable congestion or unsafe conditions with respect to the use of highways, waterways, railways, airports and airways, and other means of transportation existing or proposed which are physically located outside the municipality in which the proposed development is to be located?
(3) Does 10 V.S.A. § 6086(a) (10) require the Court •to make a de novo review of the conformity of a proposed development with a duly adopted local plan under Chapter 117 of Title 24 when the local planning commission has already found conformity and granted final subdivision approval?
(4) Is a proposed development (consisting of a mall building with two department stores, eighty satellite stores, twenty food service facilities and parking for *300 twenty-three hundred vehicles) exempt from the 10 V.S.A. § 6086(a) (9) (H) costs of scattered development criterion as a matter of law when the following structures and uses are located within one mile by road from the development site: three gas stations, a well drilling business and two vehicle sales and service businesses, the Green Mountain Power Service Center, a slaughterhouse, riding stable, roller skating rink, two multi-office buildings and four individual offices, a small multi-store building and four individual stores and seven houses and/or farms ?
(5) Does 10 V.S.A. § 6086(a) (9) (H) authorize consideration of whether projected decline in shoppers goods sales and resultant lowering of property values and reductions in tax revenues and municipal services may directly or indirectly cause additional costs of public services and facilities in a municipality which is not contiguous to the municipality in which the proposed development is to be located?
The court issued an opinion in support of its order granting permission to appeal. The court reasoned that answers to each of the certified questions could narrow the scope of the issues at trial, thereby shortening the length of the trial. Without elaboration, the court concluded that there were substantial grounds for disagreement on the court’s resolution of these issues.
II.
Interlocutory appeals are an exception to the normal restriction of appellate jurisdiction to the review of final judgments. There are weighty considerations that support the finality requirement. Piecemeal appellate review causes unnecessary delay and expense, and wastes scarce judicial resources. See Redish, The Pragmatic Approach to Appealability in the Federal Courts, 75 Colum. L. Rev. 89, 89 (1975). Furthermore, an appellate court labors under great disadvantages in disposing of interlocutory appeals. The litigants may not yet have narrowed the case’s issues sufficiently for appellate review. We are deprived of the benefits of a final trial court opinion. Interlocutory review requires us to de *301 cide legal questions in a vacuum, without benefit of factual findings. Appellate decisionmaking suffers from such abstractness. By its very nature then, interlocutory appeals impair this Court’s basic functions of correctly interpreting the law and providing justice for all litigants.
Despite those hazards, there is a narrow class of cases in which interlocutory review is nonetheless advisable. An appeal will lie in circumstances that assure the ripeness of issues for appellate review, and safeguard against improvident appellate decisionmaking. Three criteria must be satisfied. First, the appeal order must involve a “controlling question of law.” 2 V.R.A.P. 5(b). Second, there must be “substantial ground for difference of opinion” as to the correctness of that order. Id. Third, an interlocutory appeal should “materially advance the termination of the litigation.” Id. We conclude that the instant appeal satisfies none of these criteria.
V.R.A.P. 5(b) is based upon 28 U.S.C. § 1292(b) (1976) and F.R.A.P. 5. See
Castle
v.
Sherburne Corp.,
While disagreeing over some details, the federal courts have limited interlocutory appeals to “exceptional” cases. See, e.g.,
Paschall
v.
Kansas City Star Co.,
The rule’s criteria do not draw bright lines: the definitions of “controlling questions of law,” “substantial grounds for *302 difference of opinion,” and “material advancement of litigation’s termination” are not self-evident. This vagueness is deliberate as it furthers the goals of the interlocutory appeal mechanism:
The statutory purpose to inject an element of flexibility into the technical rules of appellate jurisdiction established for final judgment appeals . . . and for [other] interlocutory, appeals . . . , counsels that so long as the [trial] court has made an order, the remaining elements be treated as guiding criteria rather than jurisdictional requisites. The three factors should be viewed together as the statutory language equivalent of a direction to consider the probable gains and losses of immediate appeal.
16 C. Wright, A. Miller, E. Cooper & E. Gressman, Federal Practice and Procedure § 3930, at 156 (1977) (hereinafter cited as 16 Federal Practice and Procedure).
The flexibility of V.R.A.P. 5 (b) does not, however, give us or the trial courts license to abuse the interlocutory appeal mechanism. The “guiding criteria” of V.R.A.P. 5(b) restrict the trial court’s power to certify, and our authority to decide, interlocutory appeals to cases which are. ripe for review. Jurisdiction vests in this Court upon certification, regardless of compliance with the rule’s criteria. See
State
v.
Mahoney,
A.
Whether a question of law is “controlling” is not defined by whether the question governs the outcome of the litigation. See
Katz
v.
Carte Blanche Corp.,
We reject this contention for several reasons. First, the controlling character of a question can only be evaluated in the context of the underlying action. This suit involves numerous issues that are not a part of this appeal. All of the criteria under Act 250 must be satisfied before the appellant would be entitled to a permit. See 10 V.S.A. § 6086. Even if this Court answered each of the certified questions in the appellant’s favor, a complex trial involving numerous issues would still be necessary to resolve this case. The impact of an interlocutory decision relative to the size of this case is therefore diminished. See
Wood
v.
Wood,
Even if we were to focus upon the certified questions in isolation, their controlling nature would still be doubtful. The range of the potential answers to each of the certified questions is not limited to a “yes” or “no” response. The severity of a development’s impact on transportation, or the degree of harm to another municipality’s economy, or the extent of deviation from a local plan may prove decisive to the relevance of these factors to an Act 250 decision. Given the range
*304
of the potential answers to these questions, their controlling nature is completely dependent upon the factual record developed at trial. See
Powers
v.
State Highway Board, supra,
Hidden in the range of potential “legal” answers is an even more significant obstacle to treating these questions as “controlling questions of law.” Precisely because the certified questions could yield a range of answers, their status as purely legal questions is subject to doubt. Interlocutory appeal is proper for questions of law, not fact. V.R.A.P. 5 (b); 16 Federal Practice and Procedure § 3930, at 160. See
Wilbur
v.
University of Vermont,
This case is certainly ill-suited for appellate decision without a factual record. See
Shatkin
v.
University of Vermont,
The need for a factual record is heightened by the procedural status of this case. Act 250 authorizes a de novo proceeding in an appeal to the superior court. 10 V.S.A. § 6089(a); see
In re Preseault,
We therefore conclude that the certified questions are not “controlling questions of law” within the meaning ofV.R.A.P. 5(b).
B.
The second criterion in V.R.A.P. 5 (b) is that an interlocutory appeal “must have at least the potential to materially advance the termination of the litigation.”
Castle
v.
Sherburne Corp., supra,
The lower court’s order contended that appeal was proper because a ruling by this Court could shorten the time needed for trial. We disagree. Trial time alone is an incorrect metric. An interlocutory appeal is proper only if it may advance the
ultimate
termination of a case. See 16 Federal Practice and Procedure,
supra,
§ 3930, at 163. See also
Avery
v.
Bender, supra,
“[T]he lower courts must be mindful of this Court’s well-established policy of avoiding piecemeal appeals.”
Castle
v.
Sherburne Corp., supra,
C.
The final criterion under V.R.A.P. 5 (b) is that the appealed order involve a question on which there is “substantial ground for a difference of opinion.” Given our disposition of this appeal, we do not reach the correctness of the rulings involved in the certified questions. Nevertheless, the trial court’s conelusory treatment of this factor indicates that confusion over this criterion may also have influenced certification. Consequently, we also address this issue.
V.R.A.P. 5(b) does not supersede the trial court’s authority and responsibility to decide difficult legal issues. Trial courts should not be “bashful about refusing to find substantial reason to question a ruling of law, even in matters of first impression.” 16 Federal Practice and Procedure,
supra,
§ 3930, at 157. (Footnote omitted.) Thus, in interpreting this criterion, the courts should place little stock in the vehemence of disagreeing counsel. See
id.
§ 3930, at 157 n.6 (criticizing
Brunswick Corp.
v.
Chrysler Corp.,
Nor should the trial courts be swayed by the unique character of a particular issue. “[Interlocutory appeal] was not intended merely to provide review of difficult rulings in hard cases.”
United States Rubber Co.
v.
Wright,
“ [A] standard consistent with the policy underlying this criterion would require a trial court to believe that a reasonable appellate judge could vote for reversal of the challenged order.” Note,
supra,
The bare recitation of this criterion by the trial court in this case provided us with little guidance on why there was “substantial ground for disagreement” with the trial court’s order. The trial court should have independently evaluated the doubtfulness of its order before certifying this appeal.
III.
In
Castle
v.
Sherburne Corp., supra,
this Court held that an appeal had been improvidently granted under V.R.A.P. 5 (b). Nevertheless, we found good cause in that case to suspend the requirement of V.R.A.P. 5, and exercised our authority under V.R.A.P. 2 to answer the certified questions. See
Castle
v.
Sherburne Corp., supra,
Castle,
of course is a narrow exception to V.R.A.P. 5 that resulted from the unique situation in that appeal. There, the pattern of counsel-induced delay combined with the simplicity of the legal issues at hand, and impelled plenary consideration of the certified questions. See
id.
at 165,
The appeal is dismissed.
