请教句子的意思Enforcement is however sporadic at best

请教句子的意思Enforcement is however sporadic at best
请教 Enforcement is however sporadic at best 这个句子是什么意思.
出自下面的段落,供参考. 谢谢.
Singapore's squeaky cleanliness is achieved in part by strict rules against activities that are tolerated in other countries. For example, jay-walking, spitting, littering, and drinking and eating on public transport are prohibited. Locals joke about Singapore being a fine city because heavy fines are levied if one is caught committing an offence. Look around for sign boards detailing the Don'ts and the fines associated with these offenses, and heed them. Enforcement is however sporadic at best, and it is a common sight to see locals openly litter, spit, smoke in non-smoking zones, etc.