A speed limit of 30 mph was introduced in built-upareas.
在建筑物密集区域，限速为每小时30英里。
《柯林斯英汉双解大词典》
2
You must drop your speed in built-upareas.
在房屋密集区必须放慢速度。
《牛津词典》
3
That vision may take some time to come to fruition, as current US laws bar ultralights from flying over builtupareas, but Martin said it would eventually become reality.