Write SQL query to solve given problem: Which direction does the majority of the trains that have 3 cars are running?. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT T1.direction FROM trains AS T1 INNER JOIN ( SELECT train_id, COUNT(id) AS carsNum FROM cars GROUP BY train_id HAVING carsNum = 3 ) AS T2 ON T1.id = T2.train_id GROUP BY T1.direction