ECE R138 Quiet road transport vehicles
vehicle can travel without an internal combustion engine operating
final
https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2016/R138e.pdf
draft
https://www.unece.org/fileadmin/DAM/trans/doc/2016/wp29/ECE-TRANS-WP29-2016-026e.pdf