Thread will not execute run() when condition is met

Question

I have a Java program that is simulating one way tunnel. A semaphore represents the tunnel, and there are two threads that represent the queues of traffic waiting on either side to pass through. In main, both threads are started as well as a thread to generate cars on either side every second. When a thread realizes its queue has cars in it, it attempts to acquire the semaphore. Once it has it, it allows each car to pass through, and releases the semaphore for the other side to use.

My problem is that it only is able to pass cars on the first try. After one side has claimed and released the semaphore, it seems that it will not be able to send cars through again. It seems to be that the if statement that is checking for cars in the queue is not executing.

class leftManager extends Thread {
private int leftQueue = 0;
private int total = 0;
static Semaphore semaphore;

public leftManager(Semaphore semaphore) {
    this.semaphore = semaphore;
    this.leftQueue = leftQueue;
}
public int getQueue() {
    return leftQueue;
}
public void setQueue(int x) {
    leftQueue += x;
}
@Override
public void run() {
    try {
        while (true) {
            if (leftQueue > 0) {
                System.out.println("Catch");
                semaphore.acquire();
                for (int i = 1; i <= leftQueue; i++) {
                    int temp = (leftQueue - (leftQueue - (i - 1)));
                    leftBoundPass pass = new leftBoundPass((temp * 2) + total);
                    pass.start();
                    try {
                        leftManager.sleep(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                total += leftQueue;
                leftQueue = 0;
                semaphore.release();
                System.out.println("release");
            }
            else {
                continue;
            }
        }
    }
    catch (InterruptedException e) {
        e.printStackTrace();
    }
}
}

The rightManager is identical, other than different variable names and a different "boundPass" thread for the cars.

class leftBoundPass extends Thread {
private int car;
public leftBoundPass(int car) {
    this.car = car;
}

@Override
public void run() {
    System.out.println("Left-bound car " + car + " is in the tunnel.");
    //This is one second of sleep
    try {
        leftBoundPass.sleep(1000);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println("Left-bound car " + car + " is exiting the tunnel.");
}
}

The car generator is as follows:class trafficGenerator extends Thread {

leftManager left;
rightManager right;

public trafficGenerator(leftManager left, rightManager right) {
    this.left = left;
    this.right = right;
}

@Override
public void run() {
    int random;
    
    while (true) {
        random = (int)(Math.random() * 2);
        
        if (random == 0) {
            System.out.println("Left-bound car wants to enter the tunnel");
            left.setQueue(1);
            //System.out.println(left.getQueue());
        }
        else {
            System.out.println("Right-bound car wants to enter the tunnel");
            right.setQueue(1);
        }
        try
        {
            Thread.sleep(2000);
        }
        catch(Exception e)
        {
            System.err.println(e);
        }       
    }   
}
}

Output:

Left-bound car wants to enter the tunnel
Catch
Left-bound car 0 is in the tunnel.
Left-bound car 0 is exiting the tunnel.
release
Left-bound car wants to enter the tunnel
Right-bound car wants to enter the tunnel
Right-bound car wants to enter the tunnel