The deterioration of the sleeper support on the bal-lasted track begins with the accumulation of sleeper voids. The increased dynamic loading in the voided zone and the ballast contact conditions cause the accelerated growth of the settle-ments in the voided zones, which results in the appearance of local instabilities like ballast breakdown, white spots, subgrade defects, etc. The recent detection and quantification of the sleeper voids with track-side and onboard monitoring can help to avoid or delay the development of local instabilities. The present paper is devoted to the study of the dynamic behavior of railway track with sleeper voids in the ballast breakdown zone. The result of the experimental track-side measurements of rail acceleration and deflection is presented. The analysis shows the existence of the dynamic impact during wheel entry in the voided zone. However, the measured dynamic impact is sub-jected to the bias of the track-side measurement method. Both the mechanism of the impact and the measurement aspects are explained by using the one-beam model on viscoelastic foun-dation. The void features in the dynamic behavior are analyzed for the purpose of track-side and onboard monitoring. A prac-tical method of the void parameter quantification is proposed.