Permissible maximum masses unpacked

August 10, 2023

Do you need to determine the payload of a goods vehicle or combination of vehicles? You must adhere to the load/mass limits imposed by the National Road Traffic Act (NRTA), Act 93 of 1996, as amended.

It is important for operators to select an appropriate vehicle or combination of vehicles to enable them to convey the required payload. The NRTA prescribes limits which may not be exceeded for masses on wheels, axles, axle units, vehicles, and combinations. These masses are referred to as permissible maximum masses.

Should a person operate a vehicle on a public road in excess of the limits prescribed, any person found in contravention of the limits is guilty of an offence. Selecting the incorrect vehicle may result in an offence being committed and the vehicle being detained until the load is corrected.

In the regulations listed in this article, the NRTA specifies the legally permissible limits. Exceeding the limits imposed exposes an operator to the possibility of prosecution when weighed at a traffic control centre. Overloading results in significant damage to the road infrastructure and may impact the safe operation of the vehicle or combination.

Many operators simply subtract the tare mass(es) of the vehicle(s) from the manufacturer’s gross vehicle mass (GVM) or gross combination mass (GCM). This does not consider the additional mass of the driver, their assistant, fuel, or any other equipment fitted to or on the vehicle, which is not standard to the model. This may significantly reduce the vehicle’s payload – potentially by one tonne or more for a combination of vehicles. Taking these masses into account, the operator is using the “unladen mass” rather than “tare mass”.

The “unladen mass” should be subtracted from the “permissible maximum mass” of the vehicle or combination of vehicles, of which the GVM or GCM are just one of six aspects considered. This will allow the proper determination of the vehicle or combination’s payload.

The “permissible maximum mass” of the vehicle or combination of vehicles uses the smallest mass determined when considering the following six factors (regulation 236):

The sum of the permissible maximum axle and axle unit massloads of all axles on a vehicle or combination of vehicles (regulation 234 and 235),
The GVM or GCM of the vehicle or combination of vehicles (regulation 236 and 237),
The bridge formula (regulation 241),
Engine power in kilowatts x 240 (regulation 239(2)(b),
Drive axle mass x 5 (regulation 239(3),
The proviso in the NRTA that limits all combinations to 56,000kg (regulation 237(2).

DEFINITIONS

combination of motor vehicles – means two or more motor vehicles coupled together.

gross combination mass (GCM) – in relation to a motor vehicle which is used to draw any other motor vehicle, means the maximum mass of any combination of motor vehicles, including the drawing vehicle and load as specified by the manufacturer thereof or, in the absence of such specification, as determined by the registering authority.

gross vehicle mass (GVM) – in relation to a motor vehicle, means the maximum mass of such vehicle and its load as specified by the manufacturer thereof or, in the absence of such specification, as determined by the registering authority.

operate on a public road – or any like expression, in relation to a vehicle, means to use or drive a vehicle or to permit a vehicle to be used or driven on a public road, or to have or to permit a vehicle to be on a public road.

operator – means the person responsible for the use of a motor vehicle of any class contemplated in Chapter VI, and who has been registered as the operator of such vehicle.

public road – means any road, street, or thoroughfare or any other place (whether a thoroughfare or not) which is commonly used by the public or any section thereof or to which the public or any section thereof has a right of access, and includes:

(a) the verge of any such road, street, or thoroughfare;

(b) any bridge, ferry, or drift traversed by any such road, street, or thoroughfare; and

semi-trailer – means a trailer having no front axle and so designed that at least 15% of its tare is super-imposed on and borne by a vehicle drawing such trailer.

tare – in relation to a motor vehicle, means the mass of such vehicle ready to travel on a road and includes the mass of:

(a) any spare wheel and of all other accessories and equipment supplied by the manufacturer as standard for the particular model of motor vehicle concerned;

(b) anything which is a permanent part of the structure of such vehicle;

(d) the accumulators, if such vehicle is self-propelled by electrical power,

but does not include the mass of:

(i) fuel; and

(ii) anything attached to such vehicle which is not of the nature referred to in paragraph (b) or (c).

truck-tractor – means a motor vehicle designed or adapted:

(a) for drawing other vehicles; and

(b) not to carry any load other than that imposed by a semi-trailer or by ballast,

but does not include a tractor or a haulage tractor (see definition of tractor and semi-trailer).

REGULATIONS

Regulation 234 – Permissible maximum axle massload of vehicle

(1) No person shall operate on a public road a mini‑bus, bus, tractor or goods vehicle if the permissible maximum axle massload of such vehicle is exceeded.

(2) The permissible maximum axle massload of a vehicle shall be the least of the mass limits determined by—

(a) regulation 238(1) in respect of a vehicle fitted with pneumatic tyres or regulation 238(2) and 243 in respect of a vehicle fitted with tyres other than pneumatic tyres;

(b) regulation 239(1)(a)(ii); and

Regulation 235 – Permissible maximum axle unit massload of vehicle

(1) No person shall operate on a public road a mini‑bus, bus, tractor or goods vehicle if the permissible maximum axle unit massload of such vehicle is exceeded.

(2) The permissible maximum axle unit massload of a vehicle shall be the least of the mass limits determined by—

(a) regulation 238(1) in respect of a vehicle fitted with pneumatic tyres or regulation 238(2) and 243 in respect of a vehicle fitted with tyres other than pneumatic tyres;

(b) regulation 239(1)(a)(iii); and

Regulation 236 – Permissible maximum vehicle mass

(1) No person shall operate on a public road a mini‑bus, bus, tractor or goods vehicle if the permissible maximum vehicle mass of such vehicle is exceeded.

(2) The permissible maximum vehicle mass of a vehicle shall be the least of the mass limits determined by—

(a) the sum of all the permissible maximum axle massloads and axle unit massloads of the vehicle as contemplated in regulations 234 and 235;

(b) regulation 239(1)(a)(i);

(d) regulation 239(3); and

(e) regulation 241:

Provided that the permissible maximum vehicle mass of such vehicle shall not exceed 56,000kg.

Regulation 237 – Permissible maximum combination mass

(1) No person shall operate on a public road a combination of vehicles where the drawing vehicle is a mini‑bus, bus, tractor or goods vehicle, if the permissible maximum combination mass of such combination is exceeded.

(2) The permissible maximum combination mass of a combination of vehicles shall be the least of the mass limits determined by—

(a) the sum of all the permissible maximum axle massloads and axle unit massloads of the combination of vehicles as contemplated in regulations 234 and 235;

(b) regulation 239(1)(b);

(d) regulation 239(3); and

(e) regulation 241:

Provided that the permissible maximum combination mass of such combination shall not exceed 56,000kg.

Regulation 238 – Load on tyres

(1) No person shall operate on a public road a motor vehicle—

(a) which is fitted with pneumatic tyres, where any wheel massload is in excess of the wheel massload referred to in the appropriate part of the standard specification SABS 1550 “Motor Vehicle Tyres and Rims: Dimensions and Loads”, Part 1: “General”, Part 2: “Passenger car tyres”, and Part 3: “Commercial vehicle tyres”; or

(b) where any pneumatic tyre is not mentioned in the standard specification referred to in paragraph (a), where the wheel massload is in excess of the wheel massload approved by the manufacturer of the tyre concerned:

Provided that for the purposes of determining the pressure in a tyre the temperature of the tyre shall be disregarded.

(2) No person shall operate on a public road any vehicle fitted with tyres, other than pneumatic tyres, if the wheel massload exceeds eight kilograms per one millimetre width of any such tyre.

Regulation 239 – Gross vehicle mass, gross axle massload, gross axle unit massload, gross combination mass, power to mass ratio and axle massload of driving axle to total mass ratio not to be exceeded

(1) No person shall operate on a public road a mini‑bus, bus, tractor or goods vehicle—

(a) if—

(i) the gross vehicle mass;

(ii) any gross axle massload; or

(iii) any gross axle unit massload,

is exceeded;

(b) drawing any other motor vehicle if the gross combination mass is exceeded.

(2) No person shall operate on a public road a vehicle which is a minibus, bus, tractor or goods vehicle if the mass in kilograms of such vehicle or of a combination of vehicles of which such first‑mentioned vehicle forms a part, whether laden or unladen, exceeds a figure arrived at by multiplying the net power in kilowatts of the engine of such vehicle as determined in accordance with or calculated with due regard to SANS 10013 “The determination of performance (at net power) of internal combustion engines Part 1: Road vehicle internal combustion engines at sea level”, “The determination of performance (at net power) of internal combustion engines Part 2: Compression ignition engines at altitudes” and “The determination of performance (at net power) of internal combustion engines Part 3: Agricultural vehicle internal combustion engines at sea level”—

(a) in the case of the drawing vehicle being a tractor by 400; or

(b) in the case of any other vehicle by 240.

(3) No person shall operate on a public road a vehicle which is a mini‑bus, bus, tractor or goods vehicle if the mass in kilograms of such vehicle or of a combination of vehicles of which such first‑mentioned vehicle forms a part, whether laden or unladen, exceeds five times the total axle massload of the driving axle or axles of such vehicle:

Provided that where the drawing vehicle in a combination of vehicles is a haulage tractor, the mass in kilograms of such combination of vehicles may not exceed six times the total axle mass load of the driving axle or axles of such vehicle, whether the combination is laden or unladen.

Regulation 240 – Massload carrying capacity of road

(1) No person shall operate on a public road a motor vehicle or a combination of motor vehicles, the wheels of which are fitted with pneumatic tyres, if—

(a) the wheel massload of wheels—

(i) which are fitted to a steering axle, exceeds 3,850kg; or

(ii) which are fitted to axles other than a steering axle, exceeds 4,000kg;

(b) the axle massload of an axle fitted with two or three wheels and—

(i) which is a steering axle, exceeds 7,700kg; or

(ii) which is an axle other than a steering axle, exceeds 8,000kg;

(i) which is fitted to a vehicle designed to compact refuse and which is carrying such refuse, exceeds 10,200kg;

(ii) which is fitted to a breakdown vehicle, exceeds 10,200kg;

(iii) which is placed in the rear or middle of a bus‑train, exceeds 10,200kg;

Provided that in the case of a bus rapid transport bus-train the limit on the drive axle shall be 13,000kg and on the other non-steering axle shall be 13,000kg.

(iv) which is fitted to a bus, other than a bus‑train, exceeds 10,200kg; or

Provided that in the case of a rapid transport complementary bus, or a rapid transport trunk bus, this limit shall be 12,000kg.

(v) which is not mentioned in items (i) to (iv), exceeds 9,000kg;

(d) the axle massload of an axle unit which consists of two axles, each of which are fitted with two or three wheels, and—

(i) which is a steering axle unit, exceeds 15,400kg; or

(ii) which is an axle unit other than a steering axle unit, exceeds 16,000kg;

(e) the axle massload of an axle unit which consists of two axles, each of which are fitted with four wheels, and—

(i) which is fitted to a vehicle, except a trailer, designed to compact refuse and which is carrying such refuse, exceeds 20,400kg;

(ii) which is fitted to a breakdown vehicle, exceeds 20,400kg; or

(iii) which is not mentioned in items (i) and (ii), exceeds 18,000kg;

(f) the axle massload of an axle unit which consists of three or more axles, each of which are fitted with two or three wheels, and—

(i) which is a steering axle unit, exceeds 23,100kg; or

(ii) which is an axle unit other than a steering axle unit, exceeds 24,000kg; or

(g) the axle massload of an axle unit which consists of three or more axles, each of which are fitted with four wheels, exceeds 24,000kg; and

(h) the axle massload of an axle unit which consists of two axles, one of which is a drive axle with four wheels and the other is an axle with two wheels, and which is fitted to a rapid transport bus, if the sum of the two axle mass loads exceeds 18,200kg.

Provided that the limitations on steering axles and steering axle units in paragraph (a), (b), (d) and (f) above, do not apply to any axle or axle units which assist in reducing the turning circle of a rapid transport bus or rapid transport bus-train, but which is not the front axle or front axle unit.

Regulation 241 – Massload carrying capacity of bridges

No person shall operate on a public road a vehicle or combination of vehicles, the wheels of which are fitted with pneumatic tyres, if the total axle massload of any group of axles of such vehicle or combination of vehicles exceeds the mass in kilograms determined by multiplying the dimension of such group measured as referred to in subregulation (3) by 2,100 and adding 18,000.
A group of axles referred to in subregulation (1) may comprise any series of axles, but shall not consist of one axle unit referred to in regulation 240(d), (e), (f) or (g) alone.

(3) (a) The dimension referred to in subregulation (1) shall be measured in metres and tenths of a metre

from the centre of the first axle of any group of axles to the centre of the last axle of such group.

(b) If the dimension so measured is not a definite figure in metres and tenths of a metre, the next highest number in tenths of a metre with which the dimension so measured is exceeded shall be used for the calculation referred to in subregulation (1).

(c) Where a group of axles of a combination of vehicles is measured, the vehicles of such combination shall be positioned in line and both sides of such combination of vehicles shall be measured, and if the dimensions of the two sides differ, the longer dimension shall be used for the calculation referred to in subregulation (1).

Regulation 242 – Distribution of axle massload and wheel massload on vehicle fitted with pneumatic tyres*

Notwithstanding the provisions of regulation 240, no person shall operate on a public road a motor vehicle which is fitted with pneumatic tyres if:

on any axle with –

(i) two tyres, the wheel massload on one tyre exceeds the wheel massload on the other tyre by more than 10%; or

(ii) four tyres, the wheel massload on two tyres nearest to each other exceeds the wheel massload on the other two tyres by more than 10%;

(b) in the case of a combination of motor vehicles consisting of a truck-tractor and at least one semi-trailer, the axle massload of any steering axle or the sum of the axle massloads of any steering axle unit is less than 11% of the sum of all axle massloads of the truck-tractor and the first semi-trailer that is coupled to the truck-tractor, of the said combination of motor vehicles;

(c) in the case of a haulage tractor, whether part of a combination of vehicles or not, the axle massload of any steering axle must not be less than 15% of the sum of all the axle massloads of such haulage tractor;

(d) in the case of a motor vehicle, not being a combination of motor vehicles as referred to in paragraph (b), with a steering axle unit, the sum of the axle massloads of such steering axle unit is less than 30% of the sum of all axle massloads of such vehicle; or

Provided that in the case of a rapid transport bus-train no limit shall apply; or

(e) in the case of any other vehicle the axle massload of a steering axle is less than 20% of the sum of all axle massloads of such vehicle, except in the case of a tractor when the axle massload of the steering axle shall not be less than 12% of the sum of all the axle massloads of such tractor.

* This regulation clarifies the calculation for the 11% mass on the steering axle. Only the mass of the truck-tractor and the first semi-trailer of a combination of vehicles must be used for the calculation.

References extracted from the NRTA, Act 93 of 1996.