I do remember reading a major FPS problem with UTX concerning road traffic, if you read the UTX part in the link I posted before (http://www.simforums.com/forums/topic29041.html) it is towards the bottom. It should hopefully help you.
'Be aware that the UTX 1.2 patch increased car traffic for the USA on side streets.. many systems may find this a hard drag on perf especially in urban. The MAX car slider I would use with this is 5-7% and some older systems need to shut cars down completely by entering the UTX configuration Tool and under the ROAD SURFACE heading DISABLE moving traffic as that is the only way to remove the footprint of cars off the system.. the FSX slider for cars will not remove that footprint even when set to zero'
'Be aware that the UTX 1.2 patch increased car traffic for the USA on side streets.. many systems may find this a hard drag on perf especially in urban. The MAX car slider I would use with this is 5-7% and some older systems need to shut cars down completely by entering the UTX configuration Tool and under the ROAD SURFACE heading DISABLE moving traffic as that is the only way to remove the footprint of cars off the system.. the FSX slider for cars will not remove that footprint even when set to zero'