it's normal for cuore when the temperature needle to go up to the middle in traffic jams. Yes, if the needle goes above the middle, then one should worry and have the radiator checked and serviced. Also, make sure that when the ac compressor starts, the engine should not be too speedy, as the engine speed can also cause the rise in temperature. So, during tuning up the car, make sure the speed is rightly adjusted to the compressor.
In case you are stuck in traffic and this happens, turn off your ac manual for sometime and go easy on the accelerator paddle.