What is the maximum allowed passenger standing capacity inside a standard low-floor urban transit bus on city streets?

1. Unlimited; passengers may ride on the exterior bumpers
2. Determined strictly by the vehicle manufacturer homologation certificate and CNRT technical regulations (typically calculated as a designated number of standing passengers per square meter of clear floor area)
3. Exactly zero; no standing is ever permitted in any bus
4. Up to 200 passengers regardless of vehicle size