I'm not sure how you want it to look so i tried to make it similar to your code.
vehicle ={}
names = {}
addCommandHandler("vehicle",
function(player)
local x, y, z = getElementPosition(player)
vehicle[player] = createVehicle(411, x, y+2, z)
names[vehicle[player]] = getPlayerName(player)
setElementID(vehicle[player], "abc")
end)
addEventHandler("onVehicleEnter", root,
function(player, seat)
if getElementID(source)== "abc" and getElementModel(source) == 411 and seat == 0 then
if vehicle[player] == source then
setVehicleEngineState(source, true)
else
outputChatBox("Only "..names[source].." can drive this vehicle.", player)
setVehicleEngineState(source, false)
end
end
end)