A key consideration for implementing battery electric buses is the vehicle weight because the weight of the batteries generally makes battery electric buses heavier than an equivalent diesel bus.  However, as battery technology continues to improve it is anticipated that the difference in weight between electric and diesel buses will reduce in the future.  In New Zealand all vehicles which use public roads must comply with the Vehicle Dimensions and Mass Rule  (VDAM): vehicle-dimensions-and-mass.

Land Transport Rule: Vehicle Dimensions and Mass (VDAM) 2016

VDAM sets maximum weight limits for all vehicles for the purpose of managing road surface degradation and ensuring safety of road users. For urban buses the maximum axle mass is shown in the table below, noting that the specialist vehicle limits are only allowed for buses which have a permit from the relevant road controlling authority:

Type of axle set

Mass without a permit (kg)

Mass with a specialist vehicle permit (kg)

Single large-tyred axle

5,500

8,100

Twin-tyred axle in any axle set

9,000

12,000

Two axles in a tandem axle set comprising:

  • A twin-tyred axle with a single large-tyred axle and a 60/40 load share
  • A twin-tyred axle with a single large-tyred axle and a 55/45 load share

 

14,500

14,500

 

16,000

18,000

Two twin-tyred axles:

  • Spaced less than 1.3 metres from the first axle to the last axle
  • Spaced 1.3 metres or more from the first axle to the last axle

 

14,500

15,000

 

17,000

18,000

† For a specialist vehicle permit the single large-tyred axle must be in a tandem axle set with a twin-tyred axle with a 55/45 load share.

Table 2: VDAM 2016 schedule 3 as of 1 May 2021

The following diagram shows the different common axle configurations for urban buses, with buses with two rear axles having higher weight limits because the extra rear axle spreads the vehicle weight across a larger area:


Single rear axle

A bus with a single rear axle

Single rear axle.

 

Two rear axles

A bus with two rear axles

Two rear axles.

The maximum number of passengers which a bus is permitted to carry is determined by the lesser of two calculations which is:

  • The number of standing passengers is calculated by dividing the standing area available by 0.17m2 per passenger (as contained in Land Transport Rule: Passenger Service Vehicles 1999). The standing area plus seating capacity gives a passenger limit; and
  • Whether the gross vehicle weight exceeds the weight limit for the type of bus as specified in VDAM.  The gross vehicle weight is calculated by multiplying the number of passengers by 80kg per passenger and adding this to the unladen vehicle weight (as contained in Land Transport Rule: Passenger Service Vehicles 1999)

Land Transport Rule: Passenger Service Vehicles 1999

The table below compares the typical gross vehicle weight to the weight limit for a selection of comparable diesel and electric buses of different sizes.

Bus type

Single deck with one rear axle

Single deck with two rear axles

Double deck with one rear axle

Double deck with two rear axles

Fuel

Diesel

Battery electric

Diesel

Battery electric

Diesel

Battery electric

Diesel

Battery electric

Length

11.5m

11.4– 11.6m

12.6– 13.5m

12.6– 13.5m

10.9m

10.8m

12.4– 13.5m

12.5– 13.5m

Number of rear axles

1

1

2

2

1

1

2

2

Seats

35

35

41–43

41–43

70

70

80–85

80–85

Standing passengers

20

20

31–34

31–34

10

10

15–20

15–20

Total maximum passengers

55

55

72–75

72–75

80

80

95–100

95–100

Unladen weight

9,000 kg

11,100 – 12,500 kg

11,400 – 12,820 kg

12,800 – 15,210 kg

10,800 kg

12,300 – 13,300 kg

14,140 – 16,500 kg

16,800 – 19,000 kg

Gross vehicle weight

13,400 kg

15,580 – 16,900 kg

17,480 – 18,820 kg

18,800 – 21,280 kg

17,200 kg

18,700 – 19,700 kg

22,220 – 24,500 kg

24,480 – 27,000 kg

NZ weight limit without permit

14,500 kg

14,500 kg

20,000 kg

20,000 kg

14,500 kg

14,500 kg

20,000 kg

20,000 kg

NZ weight limit with permit

20,100 kg

20,100 kg

26,100 kg

26,100 kg

20,100 kg

20,100 kg

26,100 kg

26,100 kg

Notes:

  • Values are based on manufacturers specifications
  • Standing passenger capacity is approximate only
  • Assumes the bus has a 55/45 load share
  • Not all bus models shown are used in New Zealand

Please note that technical specifications vary between manufacturers and between bus models and therefore some buses may have specifications outside the range shown. The results show that all types of battery electric buses can fit within the New Zealand weight limits with a specialist vehicle permit being required in some instances. Battery Electric Buses which have a single rear axle or are double decker are more likely to require a specialist vehicle permit because there is a higher load placed on the axles. Some manufacturers produce single deck Battery Electric Buses which are within the standard weight limit and can therefore operate without a specialist vehicle permit. Whether a battery electric bus is above or below the weight limits depends on a number of factors including the size of bus, the number of passengers carried, the number of axles, the load share between axles, the number of batteries and the materials used for the batteries, chassis and body.

We recommend careful consideration of bus weights from a full bus network lifecycle perspective. There may be advantages to selecting lower weight buses that do not require specialist permits because they would have less restrictions in terms of where they can be used. They also may not require costly pavement upgrades or as much maintenance costs. This is because heavy weight buses, especially when fully laden, can cause rutting and potholes on surfaces that are not designed for high-stress use.

Further information related to road surface maintenance on bus routes is available here:

PTDG: Corridor inspections and maintenance requirements