1. Like Susan said, it's an insult. Calling a women stupid and a cow, which is basically calling her fat since cows are usually fat. Yet, that also be as literal as just calling an actually cow stupid.
2.It just means there not much traffic. There are not many cars on the streets.
3. Last means most recent. It means Being or coming after all others. Final.
4. Straightaway means without delay. Example: "When he heard her singing, he knew he needed to record her straightaway" and "She got to the hospital and they sne ther into the operating room straightaway"
Hope I've helped :)