aboingg The travel transition failing is not uncommon, especially on an underpowered computer or in an overloaded save but also in what look like normal circumstances. The only reliable fix is to install mods to address the reasons this can happen. If you're interested, please add NRaas Traveler, which replaces the fragile travel transition with a more reliable version, among other things.
I would strongly recommend ErrorTrap and Overwatch too, along with Register, and MasterController for its highly useful commands. All except MC do their jobs without any need for player input; MC does nothing unless you use it to issue a command. You can find more information and download links here:
If you're set on not using mods, the most you can do is reduce the strain on the game engine during the travel transition. Before you want your sims to travel:
Empty out your sims' inventories as much as is reasonable—a few items is fine, a hundred is not.
Exit to the Main Menu and drop the graphics settings as low as possible.
Turn off the interactive loading screens and the in-game shopping experience.
Quit to desktop, and delete the five cache files in Documents > Electronic Arts > The Sims 3: CASPartCache, compositorCache, scriptCache, simCompositorCache, and socialCache.
Attempt the transition immediately after reloading the save, as soon as the game clock is running.
If this works, use "save as" to rename the save, so you have a backup from before the sims traveled in case you need it later; it's always possible that the return trip will fail as well, especially with no mods in place to help. Then exit to the Main Menu, change whatever graphics settings you want, quit to desktop, reload the save, and continue playing.
