```uclid
module main {
  type state_t;
  const far : state_t;
  const near : state_t;
  const in : state_t;

  type gate_state_t;
  const up : gate_state_t;
  const down : gate_state_t;

  type controller_state_t;
  const state_0 : controller_state_t;
  const state_1 : controller_state_t;
  const state_2 : controller_state_t;
  const state_3 : controller_state_t;

  var train_state : state_t;
  var gate_state : gate_state_t;
  var controller_state : controller_state_t;

  init {
    train_state = far;
    gate_state = up;
    controller_state = state_0;
  }
  
  transition {
    train_state' = 
      switch (train_state) {
        case far : { choose(near, far) };
        case near : { in };
        case in : { far };
      };

    gate_state' = 
      switch (controller_state) {
        case state_0, state_3 : { up };
        case state_1, state_2 : { down };
      };

    controller_state' = 
      switch (controller_state) {
        case state_0 : { if (train_state == near) then state_1 else state_0 };
        case state_1 : { if (gate_state == down) then state_2 else state_1 };
        case state_2 : { if (train_state == far) then state_3 else state_2 };
        case state_3 : { if (gate_state == up) then state_0 else state_3 };
      };
  }

  // Safety property: When a train is in the "in" state, the gate must be "down".
  property safety_property {
    train_state == in -> gate_state == down;
  }
  
  // Valid initial state check.
  control {
    check;
    print_results;
  }

  invariant safety {
    train_state == in -> gate_state == down;
  }
}
```

This UCLID5 code effectively models a railroad crossing control system with transitions between different states for a Train, Gate, and Controller to ensure the gates are properly controlled in sync with the train's position. The safety property asserts that the gate must be down whenever the train is in the crossing (state "in").