The top tunnel under Poľana at the time of construction with a length of almost 2500 meters was the longest tunnel of the then Czechoslovak Republic. The excavation began in 1923 and took place simultaneously on both sides. The ceremonial breakthrough of the tunnel came on September 12, 1926, at kilometer 27,113. However, the finishing work in the tunnel lasted until the end of February 1929. The cruel tax on the construction of the tunnel was six fatal accidents during the construction of the tunnel.