Retaining walls play a critical role in railway slab tracks by significantly affecting trackbed deflection (TD), attributable to train loading. This influence, unfortunately, has been traditionally overlooked in railway retaining wall designs. This study introduces a three-dimensional numerical model that includes the slab track, a buttressed embankment, and the ground. Using the finite difference method, the model reveals insights into TD characteristics under railway loading. An artificial neural network led to the development of a metamodel to predict TD. This metamodel considered five fundamental input variables: the width, position, inclination of the retaining wall, the supported embankment's height, and the ground bearing capacity. A subsequent design strategy based on the metamodel for gravity retaining walls was proposed to control TD and prevent it from exceeding a set limit. And an explicit formula for estimating the minimum wall width required to control TD is provided. This research emphasizes the significant impact of gravity retaining wall behavior on TD, especially at the track edge close to the wall. In most cases, constraining the movement of constructed retaining walls results in less than a 10% decrease in TD.