Unity

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class RoadSpawner : MonoBehaviour
{
    public GameObject[] RoadBlocksPrefab;
    public GameObject StartBlockPrefab;

    float BlockPosX = 0;
    int BlocksCount = 7;
    float BlocksLength = 0;
    int SafeZone = 40;

    public Transform PlayerTransform;
    List<GameObject> CurrentBlocks = new List<GameObject>();
    // Start is called before the first frame update
    void Start()
    {
        BlockPosX = StartBlockPrefab.transform.position.z;
        BlocksLength = StartBlockPrefab.GetComponent<BoxCollider>().bounds.size.z;

        for (int i = 0; i < BlocksCount; i++)
        {
            SpawnBlock();
        }
    }

    // Update is called once per frame
    void Update()
    {
        CheckForSpawn();
    }

    void CheckForSpawn()
    {
        if (PlayerTransform.position.z - SafeZone > (BlockPosX - BlocksCount * BlocksLength))
        {
            SpawnBlock();
            DestroyBlock();
        }
    }

    void SpawnBlock()
    {
        GameObject block = Instantiate(RoadBlocksPrefab[Random.Range(0, RoadBlocksPrefab.Length)], transform);

        BlockPosX += BlocksLength;

        block.transform.position = new Vector3(0, 0, BlockPosX);

        CurrentBlocks.Add(block);
    }
    void DestroyBlock()
    {
        Destroy(CurrentBlocks[0]);
        CurrentBlocks.RemoveAt(0);
    }
}