Why does my train carriages phase through it to get to the back?

[Skybloxtest123561]

Why does my train carriages phase through it to get to the back?
Here’s my code.

local TrainSuperClass = {}
TrainSuperClass.__index = TrainSuperClass

local Carriages = game.ServerStorage.TrainPassengerCars
local WorkSpace = game:GetService("Workspace")
local TweenService = game:GetService("TweenService")
--local Whistle = script.Parent.WhistleSound
--local Chuffing = script.Parent.ChuffingSound

function TrainSuperClass.new(TrainModel, Nodes)
    local Train = {}
    
    setmetatable(Train, TrainSuperClass)
    
    Train.Nodes = Nodes
    Train.TestModel = TrainModel
	Train.Node = 0
	Train.LastCarriage = nil
	Train.Connections = {}
	
    
    coroutine.wrap(function()
        wait(1)
        Train:Setup()
    end)()
    
    return Train
    
end


function TrainSuperClass:Setup()
    self.Train = self.TestModel:Clone()
    
    if not(self.Nodes:FindFirstChild("Node" ..self.Node)) then
        warn("Cannot find node" ..self.Node)
        return
    end
    
    local Children = (self.Train:GetChildren())
    
    for i = 1, #Children do
        if (Children[i] ~= self.Train.PrimaryPart) then
            local Weld = Instance.new("Weld")
            Weld.Part0 = Children[i]
            Weld.Part1 = self.Train.PrimaryPart
            Weld.C0 = Children[i].CFrame:inverse()
            Weld.C1 = self.Train.PrimaryPart.CFrame:inverse()
            Weld.Parent = self.Train.PrimaryPart
        end
    end
    
    self.Train.Parent = WorkSpace.Train
    self.Train:SetPrimaryPartCFrame(self.Nodes:FindFirstChild("Node" ..self.Node).CFrame + Vector3.new(0,self.Train.PrimaryPart.Size.Y/2,0))
	
	local Killer = self.Train:FindFirstChild("Killer")
	
	if Killer then
		local KillPart = Killer.Touched:Connect(function(hit)
			if hit.Parent:FindFirstChild("Humanoid") then
				hit.Parent:FindFirstChild("Humanoid").Health = 0
			end
		end)
		
		table.insert(self.Connections, KillPart)
	end
	
	self:Move()
end

function TrainSuperClass:GetTime(Distance)
    return Distance / self.Speed
end

function TrainSuperClass:Carriages(Node)

	local Carriage = Carriages:GetChildren()[math.random(1,#Carriages:GetChildren())]:Clone()
	local All = Carriage:GetChildren()

	for A = 1, #All do
		if (All[A].Name ~= self.Train.PrimaryPart and All[A]:IsA("BasePart")) then
			local NewWeld = Instance.new("Weld")
			NewWeld.Name = "Weld"
			NewWeld.Part0, NewWeld.Part1 = All[A], Carriage.PrimaryPart
			NewWeld.C0 = All[A].CFrame:inverse()
			NewWeld.C1 = Carriage.PrimaryPart.CFrame:inverse()
			NewWeld.Parent = Carriage.PrimaryPart
		end
	end

	if not self.LastCarriage then
		self.LastCarriage = self.Train
	end

	Carriage:SetPrimaryPartCFrame(self.LastCarriage:GetPrimaryPartCFrame() * CFrame.new(-Carriage.PrimaryPart.Size.X, 0, 0))

	self.LastCarriage = Carriage
	Carriage.Parent = WorkSpace.Train

	spawn(function()
		self:MoveCarriage(Node, Carriage)
	end)
end

function TrainSuperClass:MoveCarriage(NodeNum, Carriage)
	local Node = self.Nodes:FindFirstChild("Node"..NodeNum)

	if not (Node) then
		Carriage:Destroy()
		return
	end

	local Distance = (Carriage.PrimaryPart.Position - Node.Position).Magnitude

	local Time = self:GetTime(Distance)

	local TweenInfo = TweenInfo.new(
		Time,
		Enum.EasingStyle.Linear,
		Enum.EasingDirection.In,
		0,
		false,
		0
	)

	TweenService:Create(Carriage.PrimaryPart, TweenInfo, {CFrame = Node.CFrame + Vector3.new(0,Carriage.PrimaryPart.Size.Y/2,0)}):Play()

	wait(Time)

	self:MoveCarriage(NodeNum + 1, Carriage)
end

function TrainSuperClass:Move()
	self.Node = self.Node + 1

	local Node = self.Nodes:FindFirstChild("Node"..self.Node)

	if not (Node) then
		self:Stop()
		return
	end

	if self.Node == 1 then
		
		local All = self.Train:GetChildren()

		for A = 1, #All do
			if (All[A].Name ~= self.Train.PrimaryPart and All[A]:IsA("BasePart")) then
				local NewWeld = Instance.new("Weld")
				NewWeld.Name = "Weld"
				NewWeld.Part0, NewWeld.Part1 = All[A], self.Train.PrimaryPart
				NewWeld.C0 = All[A].CFrame:inverse()
				NewWeld.C1 = self.Train.PrimaryPart.CFrame:inverse()
				NewWeld.Parent = self.Train.PrimaryPart
			end
		end
		
		wait(7)
		self.Train:SetPrimaryPartCFrame(Node.CFrame + Vector3.new(0, self.Train.PrimaryPart.Size.Y/2, 0))

		for i = self.CarriagesCount,1,-1 do
			self:Carriages(self.Node)
		end
		
		--Whistle:Play()
		self:Move()
		--Chuffing:Play()
		--Chuffing.Looped = true
		
		return
	end

	local Distance = (self.Train.PrimaryPart.CFrame.p - Node.CFrame.p).Magnitude

	local Time = self:GetTime(Distance)

	local TweenInfo = TweenInfo.new(
		Time,
		Enum.EasingStyle.Linear,
		Enum.EasingDirection.In,
		0,
		false,
		0
	)


	TweenService:Create(self.Train.PrimaryPart, TweenInfo, {CFrame = Node.CFrame + Vector3.new(0,self.Train.PrimaryPart.Size.Y/2,0)}):Play()

	wait(Time)

	self:Move()
end

function TrainSuperClass:Stop()
	wait(5)
	
	for _, v in next, self.Connections do
		v:Disconnect()
	end
	
	self.LastCarriage = nil
	self.Train:Destroy()
	self.Train.Parent = nil
	self.Node = 0
	self:Setup()
end

return TrainSuperClass

Thanks!