How to make a racing game in Roblox Studio

local Players = game:GetService("Players")

local race = workspace:WaitForChild("Race")
local checkpoints = race:WaitForChild("Checkpoints")
local gate = race:WaitForChild("StartGate")

local LAPS = 3
local MAX_RACE_SECONDS = 300
local COUNT = #checkpoints:GetChildren()

local running = false
local startTime = 0
local progress = {} -- [player] = { next = 2, lap = 0, finished = false }
local finishers = 0

local function status(text)
	race:SetAttribute("Status", text)
end

-- The player touching a checkpoint, on foot or driving a car.
local function playerFromHit(hit)
	local model = hit:FindFirstAncestorOfClass("Model")
	while model do
		local player = Players:GetPlayerFromCharacter(model)
		if player then
			return player
		end
		local seat = model:FindFirstChildWhichIsA("VehicleSeat", true)
		if seat and seat.Occupant then
			return Players:GetPlayerFromCharacter(seat.Occupant.Parent)
		end
		model = model:FindFirstAncestorOfClass("Model")
	end
	return nil
end

for _, part in checkpoints:GetChildren() do
	local index = tonumber(part.Name)
	part.Touched:Connect(function(hit)
		if not running then
			return
		end
		local player = playerFromHit(hit)
		local state = player and progress[player]
		-- Only the next checkpoint counts, so shortcuts don't work.
		if not state or state.finished or index ~= state.next then
			return
		end
		if index == 1 then
			state.lap += 1
			if state.lap >= LAPS then
				state.finished = true
				finishers += 1
				status(string.format("%s finished #%d in %.2f s", player.DisplayName, finishers, os.clock() - startTime))
				return
			end
		end
		state.next = index % COUNT + 1
	end)
end

local function racersLeft()
	local left = 0
	for player, state in progress do
		if player.Parent and not state.finished then
			left += 1
		end
	end
	return left
end

while true do
	running = false
	gate.CanCollide = true
	gate.Transparency = 0.5
	while #Players:GetPlayers() == 0 do
		status("Waiting for players")
		task.wait(2)
	end
	for seconds = 10, 1, -1 do
		status("Race starts in " .. seconds)
		task.wait(1)
	end

	progress, finishers = {}, 0
	for _, player in Players:GetPlayers() do
		progress[player] = { next = 2, lap = 0, finished = false }
	end
	gate.CanCollide = false
	gate.Transparency = 1
	status("GO!")
	startTime = os.clock()
	running = true

	repeat
		task.wait(0.5)
	until racersLeft() == 0 or os.clock() - startTime > MAX_RACE_SECONDS

	running = false
	status("Race over")
	task.wait(8)
end