SC4 time going all wacko

For some reason when i went back to playing one of my cities in simcity4
rush hour the cars and busses were all over the place. That is to say they
ARE all over the place - almost as if time is slowing down and speeding up
all at random intervals. I have no control over it, the only thing i know is
that it has made udriveit missions almost IMPOSSIBLE to complete as cars
appear out of nowhere infront of the car you are driving and eventually you
blow up. I have updated to the most recent patch, am running only a few of
the official mods (landmark ones) and no other mods/plugins. Graphics
drivers are all up to date, computer has no problem running the game, its
just the cars that have gone wacko - to the extent that clicking the pause
button no longer actually pauses cars on the roads, and for some reason
having the timespeed at max makes the cars slow down almost to a normal
speed, but then sudden bursts of time catchup. Is there a way to solve this
problem? Maybe its a known issue with nvidia cards?

thanks

M