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The prescribed braking performance for a motor vehicle or trailer is dependent upon its category as follows:
* Does not include any load imposed on the towing vehicle.
The prescribed braking performance for motor vehicles requires that BOTH the stopping distance and the mean fully developed deceleration (MFDD) are fulfilled.
| Vehicle Category | Initial Speed (km/h) | Stopping Distance (m) | MFDD m/sec2 |
| M1 | 80 | 50.66 | 5.8 |
| M2 | 60 | 36.69 | 5.0 |
| M3 | 60 | 36.69 | 5.0 |
| N1 | 80 | 61.23 | 5.0 |
| N2 | 60 | 36.69 | 5.0 |
| N3 | 60 | 36.69 | 5.0 |
The above performance must be achieved in both laden and unladen condition.
| Vehicle Category | Initial Speed (km/h) | Stopping Distance (m) | MFDD m/sec2 |
| M1 | 80 | 9.333 | 2.9 |
| M2 | 60 | 64.38 | 2.5 |
| M3 | 60 | 64.38 | 2.5 |
| N1 | 70 | 95.71 | 2.2 |
| N2 | 50 | 50.97 | 2.2 |
| N3 | 40 | 33.82 | 2.2 |
The above performance must be achieved in both laden and unladen conditions. The secondary brake performance may be achieved via the service brake control with half system failure or by a separate control device.
| Vehicle Category | Initial Speed | Stopping Distance(m) Laden | Stopping Distance(m) Unladen | MFDD m/sec2 Laden | MFDD m/sec2 Unladen |
| M1 | 80 | 150.22 | 178.66 | 1.7 | 1.5 |
| M2 | 60 | 101.3 | 119.76 | 1.5 | 1.3 |
| M3 | 60 | 101.3 | 101.3 | 1.5 | 1.5 |
| N1 | 70 | 152.52 | 180.93 | 1.3 | 1.1 |
| N2 | 50 | 79.96 | 94.45 | 1.3 | 1.1 |
| N3 | 40 | 52.37 | 52.37 | 1.3 | 1.3 |
Residual service brake performance is that required in the event of a failure in part of the transmission of the service braking system.
IN ALL CASES THE RESPECTIVE PRESCRIBED BRAKE PERFORMANCE MUST BE ACHIEVED WITHOUT LOCKING THE WHEELS.
The parking brake should be capable of holding the laden vehicle stationary on a 18% up or down gradient. In the case of vehicles authorised to tow a trailer the parking brake of the towing vehicle must be capable of holding the laden combination on a 12% up or down gradient.
Trailers of category O1 need not be fitted with a service brake system but if such a trailer is so equipped then it should meet the same requirements as a Category O2 trailer.
The braking force developed for the braked wheels shall be "X" per cent of the maximum stationary wheel load where "X" has the following values that shall apply to both the laden and unladen conditions:-
THE ABOVE PERFORMANCE MUST BE ACHIEVED WITHOUT ANY LOCKING OF WHEELS
N.B. There are no performance levels prescribed for secondary and residual performance.
Brake related problems are one of the principal reasons for annual LGV test failure and for attracting prohibitions during a roadside check. Operators have a legal and moral responsibility to ensure that their vehicle braking systems meet all statutory requirements. The following table lists the in service requirements for service, secondary and park brakes on motor vehicles and trailers post 1968. Operators of older vehicles information can be obtained from Midland Grau on 0527 510310.
| Vehicles | Post 1968 Service | Post 1968 Secondary | Post 1968 Parking | Type Approved Service | Type Approved Secondary | Type Approved Parkimg |
| 1. Rigid Vehicles | ||||||
| (A) Not designed for towing | ||||||
| (ii) 2 axle | 50% GVW | 25% GVW | 1 in 6.25* | 50% GVW | 25% GVW | 16% GVW |
| (ii) more than 2 axles | 50% GVW | 25% GVW | 1 in 6.25* | 50% GVW | 25% GVW | 16% GVW |
| (B) Designed for towing | 50% GVW | 25% GVW | 1 in 6.25* | 50% GVW | 25% GVW | 16% GTW |
| 16% GVW | ||||||
| Articulated Tractors with: | ||||||
| (A) Secondary brake on tractor only | 50% GVW | 25% GVW | 1 in 6.25* | |||
| (B) Secondary brake on tractor & trailer | 50% GVW | 25% GVW | 1 in 6.25* | 50% GVW | 25% GVW | 12% GTW |
| 16% GVW |
| Trailer manufactured on or after 1 October 1982 | Trailer manufactured on or after 1 October 1982 | |||
| 1. Semi Trailers | ||||
| (A) GVW 6100kg or more | 0.4TAW | 1 in 6.25* | 0.45TAW | 16% GVW |
| (B) GVW less than 6100kg | 0.4TAW | 1 in 6.25* | 0.45TAW | 16% GVW |
| 2. Drawbar Trailers | 0.4TAW | 1 in 6.25* | 0.45TAW | 16% GVW |
Definitors:
1. POST 1968 First used on or after 1 January 1968 having a manufacturer's plate.
2. TYPE APPROVED. Manufactured on or after 1 October 1982 and first used on or after 1 April 1983 and has been issued with (a) a National Type Approval Certifacte of Conformity or (b) a Minister's Approval Certificate, or, (c) a Type Approval Certificate issed by an EEC member state.
3. GVW = gross vehicle weight GTW gross train weight TAW total axle(s) weight
4. * 1 in 6.25 is equivalent to 16% GVW
5. Design weights should be used if higher than the Construction & Use weights.
Local Authorities operate a wide variety of vehicles and the legal requirements are complicated by the fact that the many exemptions and concessions which benefit certain local authority vehicles do not apply across the board. The following paragraphs outline the position for many specialised types of vehicles.
Many local authority vehicles are operated for normal road use and therefore frequently have to comply with the full requirement of the Road Vehicles (Construction and Use) regulations 1986. There are, however, exceptions for certain categories of vehicles and the most relevant of those are detailed below. (information kindly supplied by the Freight Transport Association).
Required to meet C&U regs in full unless:
Antilock braking systems must now be fitted to the following classes of goods vehicles and trailers:
NB: It is legally permissible to drive a vehicle with a fault in its antilock braking system in order to complete a journey if the fault arose after the journey began, or to move the vehicle to a place where the fault will be repaired. However this would not apply if the braking system does not meet the laid down braking efficiency requirements.
EEC braking directive 71 /320 in its current form states that commercial vehicles will be fitted with the dedicated ABS power supply to ISO standard 7638. For an interim period a footnote applies to the effect that, on a trailer, the vehicle manufacturer will fit:
1) An ISO 7638 cable or supplementary cable (24S also known as ISO 3731)
2) ABS powering via the stop lamp (24N otherwise known as ISO 1185) or a load-sensing valve.
3) A trailer mounted ABS warning light. Since goods vehicles produced within the last three years have all had ISO 7638 power provided at the coupling, the need for additional provision of trailer ABS powering to 24S is becoming much reduced.
| Category | Legislation | Vehicle Type | Weight Range | New Approvals | New Registrations |
| N2/N3 | Fitment of auto brake wear adjustment devices | Goods vehicles | All goods vehicles | October 1992 | October 1994 |
| O3/O4 | Fitment of auto brake wear adjustment devices | Trailers | All 3.5 tonnes | October 1992 | October 1994 |
| N3 | Mandatroy ABS | Goods vehicles | Above 12 tonnes | October 1996 | October 1998 |
| N2 | Mandatroy ABS | Goods vehicles | 7.5 to 12 tonnes | April 1998 | April 2000 |
| N2 | Mandatroy ABS | Goods vehicles | 3.5 to 7.5 tonnes | April 1998 | April 2001 |
| O3 | Mandatroy ABS | Trailers | Above 5.0 tonnes | April 1998 | April 2000 |
| O3 | Mandatroy ABS | Trailers | 3.5 to 5.0 tonnes | April 1999 | April 2001 |
| M3 | Mandatroy ABS | Passenger Vehicles | Above 12 tonnes | April 1998 | April 2000 |
| M3 | Mandatroy ABS | Passenger Vehicles | 5 to 12 tonnes | April 1998 | April 2000 |
| M2 | Mandatroy ABS | Passenger Vehicles | Up to 5.0 tonnes | April 1998 | April 2000 |
The EEC directive coming into force on 01.10.94 for all new registrations dictates that European Governments may introduce a requirement for automatic brake wear adjustment. NB: UK C&U regs require fitment of auto brake wear adjustment from 1 April 1995. The directive prescribes that after the heating and cooling of the brake(s) during Type 1 and Type 11 fade tests, the wheels must rotate freely. This rule can be readily implemented on motor vehicles, as each vehicle type is subject to the respective fade test and therefore the performance of the automatic brake wear adjustment device can be checked. However, in the case of trailers, fade test assessment is carried out on an individual brake and a certificate of conformity issued. To meet the new requirements, the fade tests would need to be repeated which would incur considerable time and cost penalties on the trailer manufacturer. For this reason the Department of Transport has agreed to amend the C&U requirements to include an exemption which has been added in a future directive.