Hey,
I have a problem with my computer and roller coaster tycoon 3. I got the game about a week ago now, and when i first started playing it ran pretty well. Though since the second day I started playing it it lags. It will run fine for a few minutes anywhere from 3-15 minutes. Then it will start lagging and running slow, and it gets worse and worse and worse as time goes on until its pretty much just so laggy i don't want to play anymore. Also it starts lagging sooner if I don't have the rides going and the peeps moving about. I've tried changing the graphical settings but there's no difference from having it at the highest settings to the lowest settings. I honestly don't know what to do anymore. Please help!
Thanks,
Fishy!

Also:
If I restart the game it runs fine again then starts doing the same thing as before so I keep having to restart to fix it!

its probably your graphics card

If you search "How to run RCT3 faster" on Google, ehow.com has a great tutorial that should help.

Omg Drew we posted at the same time :P

Well
heres my grapics card:

Video Card: ATI Radeon HD 4270
Manufacturer: ATI
Chipset ATI Radeon HD 4270
Dedicated Memory 256 MB
Total Memory 1.9 GB
Pixel Shader Version 4.1
Vertex Shader Version 4.1
Hardware T & L Yes
Vendor ID 1002
Device ID 9712
Plug and Play ID VEN_1002&DEV_9712&SUBSYS_2AAC103C&REV_00
Driver Version 8.733.0.0

Well
heres my grapics card:

Video Card: ATI Radeon HD 4270
Manufacturer: ATI
Chipset ATI Radeon HD 4270
Dedicated Memory 256 MB
Total Memory 1.9 GB
Pixel Shader Version 4.1
Vertex Shader Version 4.1
Hardware T & L Yes
Vendor ID 1002
Device ID 9712
Plug and Play ID VEN_1002&DEV_9712&SUBSYS_2AAC103C&REV_00
Driver Version 8.733.0.0

You might want to try adjusting the virtual memory it may help. https://www.youtube.com/watch?v=3DNVRGbeiMM or https://youtu.be/fM2EMCuq7cU (Making computer faster by upgrading virtual RAM). If you try this, I would back up your computer first and the projects you've been working on.

Hi - my experience has been that on occasion I have a problem with what seems to be the game itself "freezing" but not really freezing. Sometimes when I am placing a lot of scenery or working very quickly it begins to lag. I have a very good GPU (HD7970) and my processor is overclocked to 4.5ghz so it's not about that. I also have 16 Gb of memory so that is also not the issue. Try turning on the fps cheat by naming a peep...fps☺ In the upper left corner you will see the frame rate displayed. Watch as you move about the park and play to see if and when the fps drops. This may help you determine what is causing the issue. When mine goes below 100☺ I move away from the park to an area outside and get an instant "refresh" of my fps. If this doesn't work for you at least it may give you more insight. 
Also these things have been shown to cause massive drops in performance-
Too much pool (I saved and removed an entire pool complex and the difference was HUGE!)
Too much water (if you have many water features the game is always trying to reflect)
Too much (sic) animals 
Too much (sic) peeps (when I have more than 3000 peeps my game begins to slow considerably)
Too much anything else xD
Try to build lots of space between rides and coasters. It's hard, I know☺ The peeps won't care and you'll have more room to decorate. Just don't forget the benches and bathrooms.
I play using win7 and not in XP compatibility mode. I know this is long. I want to post more.
Let me know how it goes and if I/we can still help.