Server

local CurrentLevel = 0;

local GEARSHIFT = "back";
local CLUTCH = "left";

rednet.open("TOP");

while true do
    local id, message = rednet.receive();
    if message == "stop" then -- if cab has reached destination
        redstone.setOutput(CLUTCH, true);
    elseif type(message) == "number" then
        if not message == CurrentLevel then
            local isUp = message > CurrentLevel;
            CurrentLevel = message;

            rednet.send(id, isUp);

            redstone.setOutput(GEARSHIFT, isUp);
            redstone.setOutput(CLUTCH, false);
        end
    end
end