John Daniel Taunton died from injuries he sustained in an automobile collision on April 11, 1993. Appellee Raymond Taunton filed a complaint for the wrongful death of his son on December 1, 1993. Appellant Georgia Department of Transportation (“DOT”) filed its answer, which included several defenses. Taunton subsequently filed a motion to strike three of the DOT’s defenses, which were based on the expert affidavit requirement, OCGA § 9-11-9.1, exceptions to the *233Georgia Tort Claims Act, OCGA § 50-21-20 et seq., and the “public duty doctrine,” respectively. The motion was granted as to those defenses based on OCGA § 9-11-9.1 and the public duty doctrine, but denied as to the DOT’s defense under the Tort Claims Act. The order was certified for interlocutory review, the DOT’s application was granted by this court, and this appeal followed.
OCGA § 9-11-12 (f) provides that “[u]pon motion made by a party within 30 days after the service of the pleading upon him, or upon the court’s own initiative at any time, the court may order stricken from any pleading any insufficient defense or any redundant, immaterial, impertinent, or scandalous matter.” Generally, “[s]uch motions to strike are not favored and should not be granted unless it is clear that the matter sought to be stricken can have no possible bearing upon the subject matter of the litigation. [Cit.]” Medlin v. Carpenter, 174 Ga. App. 50, 55 (10) (329 SE2d 159) (1985). Defensive pleadings in particular “are to be liberally construed in favor of the pleader, and a motion to strike a defense should not be granted unless it appears to a certainty that the plaintiff would succeed despite any state of facts which could be proved in support of the defense.” Wellbaum v. Murphy, 122 Ga. App. 654, 655 (178 SE2d 690) (1970).
Moreover, although there is very little authority in Georgia generally on what constitutes an “insufficient” defense under OCGA § 9-11-12 (f), it would appear obvious that the procedure should not be used to dispose of weighty matters of law. In this regard, we find particularly persuasive the view taken in Resolution Trust Corp. v. Youngblood, 807 FSupp. 765 (N. D. Ga. 1992), and cases cited therein as to Rule 12 (f) of the Federal Rules of Civil Procedure. “Where a defense is insufficient as a matter of law, it should be stricken to eliminate the unnecessary delay and expense of litigating it. However, motions to strike cannot be used to determine disputed fact questions, nor can they be used to decide disputed and substantial questions of law, particularly where there is no showing of prejudice to the movant. Even when the defense presents a purely legal question, the courts are very reluctant to determine disputed or substantial questions of law on a motion to strike; these questions quite properly are viewed as determinable only after discovery and a hearing on the merits. To do otherwise would be to run the risk of offering an advisory opinion on an abstract and hypothetical set of facts.” (Citations and punctuation omitted.) Id. at 769.
We examine the “sufficiency” of each of the DOT’s stricken defenses under these formidable standards.
1. DOT’s third defense states: “Plaintiff failed to file an expert affidavit pursuant to OCGA § 9-11-9.1. Therefore, to the extent Plaintiff alleges that DOT engaged in professional malpractice, Plaintiff’s complaint should be dismissed for failure to state a claim.” Taunton *234is asserting that DOT should have installed advance warning signs, rumble strips, a crossroad sign, flashing lights, etc., none of which previously existed at the intersection.
The DOT argues that such matters are for professional traffic engineers to determine and that any alleged shortcoming in that decisionmaking process would sound in professional negligence. “The process of building and designing roads requires engineering services which have been described as the performance of professional services within the purview of OCGA § 9-11-9.1. [Cits.]” Dept. of Transp. v. Gilmore, 209 Ga. App. 656 (434 SE2d 114) (1993). Under the circumstances, we cannot say that “it appears to a certainty that the plaintiff would succeed despite any state of facts which could be proved in support of the defense.” Wellbaum v. Murphy, supra. The trial court erred in striking this defense.
2. The question of whether the DOT’s defense based on the “public duty” doctrine established in City of Rome v. Jordan, 263 Ga. 26, 27 (426 SE2d 861) (1993), should be limited to cases where third party negligence is involved is indisputedly a “substantial question of law.” Youngblood, supra. We do not reach the substance of this weighty matter given the lack of factual development of the record at this stage of the case. We merely hold that a motion to strike under OCGA § 9-11-12 (f) was not the appropriate vehicle to dispose of the DOT’s “public duty” defense at this juncture.
Defenses that are clearly insufficient based on established law should be readily stricken even “upon the court’s own initiative,” OCGA § 9-11-12 (f). However, we find the importance of further developing the record on this particular issue to outweigh consideration of the delay and expense to Taunton necessitated by the DOT’s reliance on City of Rome v. Jordan, supra.
Judgment reversed.
Beasley, C. J., Birdsong, P. J., Pope, P. J., Andrews, Johnson and Ruffin, JJ., concur. McMurray, P. J., and Blackburn, J., dissent.