In a large bowl, mix together cucumbers, onion, bell peppers, and carrots. Set aside.
In a medium saucepan, combine salt, white vinegar, sugar, celery seed, mustard seed, and crushed red pepper. Bring to a boil and boil for 2-3 minutes. Remove from heat and let cool completely.
Combine vinegar mixture with cucumber mixture. Stir well. Cover and refrigerate.