Under Chinese passenger transport safety regulations, what are the statutory passenger capacity rules regarding standing passengers (站立乘客) on highway express passenger coaches (公路客运车辆)?

1. Standing passengers are permitted up to 20% of seating capacity
2. Standing passengers are permitted provided they hold onto seat headrests
3. Standing passengers are allowed on expressways during holiday travel rush (春运)
4. Highway express coaches and tourist passenger buses are strictly prohibited from carrying any standing passengers; total passenger headcount must never exceed certified seated capacity (严禁站人)