测量乘用车和轻型卡车燃油系统蒸发排放的高度首选的SAE推荐实践是SAE J171中详述的封闭技术。封闭技术的灵敏度和准确性优于陷阱法。保留这一推荐做法以供历史参考，并用于进口到美国的旧车。此外，SAE J171a中引用了这种捕集方法，用于进行实际上无法在外壳中进行的运行损耗测量。排放量是在一系列实验室测试中测量的，这些测试模拟了夏季大都市地区的典型车辆使用情况。

The highly preferred SAE Recommended Practice for measuring evaporative emissions from fuel systems of passenger cars and light trucks is the enclosure technique detailed in SAE J171. The sensitivity and accuracy of the enclosure technique is superior to that of the trap method. This recommended practice is retained for historical reference and for use with older vehicles imported into the United States of America. In addition, this trap method is referenced in SAE J171a for making running loss measurements which cannot practically be made in an enclosure. Emissions are measured during a sequence of laboratory tests that simulate typical vehicle usage in a metropolitan area during summer months.