Airplanes have to wait for a train to cross the runway at airport

Routing a railway line through the middle of a busy street is one thing, but what about through an airport? 
On the eastern coast of New Zealand’s North Island is Gisborne Airport. It is an undersized airport and covers 160 hectares. 
It has one major claim to fame as a train line runs right across the main runway. 
Not many trains have to get permission from Air Traffic Controllers in order to continue on their journey, but the Palmerston North – Gisborne Railway Line does. 
The airport only operates between 6:30 am and 8:30 pm and outside of these times, trains can travel as they see fit.