The Sirat's vivid description, a bridge thinner than a hair and sharper than a sword, crossed at speeds according to one's deeds, is typical of a whole category of Islamic eschatological material, and mainstream Sunni theology developed an explicit methodological principle, bila kayfa, "without asking how," specifically to handle it.
The principle holds that certain revealed descriptions, whether of God's attributes or of eschatological realities such as the bridge and the scales, are to be affirmed as true in the manner God and the Prophet intended, without either denying their reality as pure metaphor or pressing them into a fully specified literal mechanism the mind can interrogate. The formula is associated above all with the traditionalist and later Ash'ari handling of the divine attributes, where verses describing God's hand or face are affirmed without asking how, avoiding both an anthropomorphism that makes God resemble creatures and a rationalizing denial that empties scripture of content; the same method extended naturally to the eschatological furniture.
The alternative, argued from the Mu'tazili side, was to treat such descriptions as figurative representations of realities better captured in abstract terms, exact justice rather than a literal scale, on the ground that a scale must weigh a physical quantity and a bridge must have physical dimensions, neither of which self-evidently applies to actions or souls. The dispute over the Sirat is a specific instance of the larger argument about how literally revealed description should be read, one where the traditionalist bila kayfa position became, and remains, dominant in both major Sunni creedal traditions and in Twelver Shia theology's own broadly similar handling of the same material.