I am new to model railroading and I have set up my track. My setup is an Atlas Trainman N scale starter kit. On the setup that came with the kit, (an oval) everything runs great even at full speed. I have set up my own layout with a different code (80) rail and I have some switches. Anytime my cars hit the switch, the locomotive continues fine but the rest of the train derails.
I have tried weighting the cars with bb’s but they still derail at switches going very slowly or quickly.
Do yourself a favour and get an NMRA Gauge (any decent Hobby Shop should carry them) and then go to the Fast tracks website. Check the Video’s listing and you will find an excellent video on how to use the gauge for checking all the parts of your switches to see if they are all within spec. You can also check your track with it and check ALL your wheels to see if all Loco’s and rolling stock wheels are in gauge.
Another thing to check is to make sure that your Point Rail stays firm against the Stock Rail as the cars roll through the turnout. Also, make sure that all your track joints are level and square and fit snugly together.
Also, go to the NMRA website and print off a copy of the recommended practices car weight table and make sure that all your rolling stock is close to what is recommended. Just throwing a bunch of BB’s into a car will not ensure that it will run well unless ALL your cars weigh the same, or reasonably close to the same.
Good Luck with your "N"ormal scale trains. That’s what I have.
Blue Flamer.
What kind of turnouts (track switches)? Some types need a way to keep the points (the moving part of the switch) solidly against the rails.
Or, the track switches may be out of gauge. Or, the wheels may be out of gauge, especially if they are cheaper cars…
Need more info about your trains and tracks.
Atlas Code 80 turnouts are notorious for having wobbly / loose points: check the fit at the throwbar.
Sometimes all you need is a shot of CA at the base of the points.
The point rails also sometimes stick way out, even when flush: a few passes with a file can fix that.
They also have funky plastic frogs which can bump flanges / wheels up and over. Check to see if any plastic bumps stick out.
As the cars pass by get down and see exactly where the cars derail.
And, of course, make sure your wheels are in guage 
(As previously posted, a NMRA guage is your best buddy here)
Hope this helps.
jmastersdds, You should know that this is not just an N scale thing. It happens with all of the scales.
I would push a car with your hand by itself across the switch and look of any wheel abnormal movement at any point. Also you will be able to feel if a wheel hits on a point end.
Some times the point track end gets bend away a little from the rail. Also I have had to round the top of some point rails as it would catch a car wheel.
I have had to spend time fixing some of my switches, but it is worth it to get the cars and engines to run correctly through. I have also had to replace some switches as I could not get them fixed or I destroyed it trying.[:'(]
Those of use that have a really good operating model railroad know that there will lots of tweaking and even replacing of items. But less so as we learn more. Unfortunately, just like the real thing.