Today, the DfT has finally rubber-stamped the use of Longer Semi Trailers (LSTs) for general use on UK Roads. This follows their press release earlier this month suggesting that legislation would be laid on 10 May to safely roll out the vehicles from 31 May.
Many believed that operators would be able to run LSTs like standard 13.7m long trailers when they became legal and that the existing length regulations would be increased by 2.05m to suit. That's not quite how this is going to be governed.
The existing Road Vehicles (Construction and Use) Regulations 1986 will remain unchanged. LSTs have been added as a new trailer type under the new 2023 No. 524 Road Vehicles (Authorisation of Special Types) (General) Order 2023 (commonly known as STGO), and yes, caveats are in place for those wanting to operate LSTs under the new statutory regime.
Legal requirements under the newly amended regulation include:
- Route plans and risk assessments for each route, including diversionary routes.
- Copies of route plans and risk assessments to be carried in the towing vehicle and retained for 2 years.
- Pre-notification to the Secretary of State of intent to operate LSTs — via the Vehicle Operator Licensing (VOL) system. This requirement is set to last for an initial 5-year period.
Interestingly, in addition to these legal requirements, there are guidance measures relating to:
- Driver training and scheduling
- Record keeping
- Training for transport managers and other key staff
- Safe and appropriate loading practices
Longer Semi Trailers which enter into service from today will automatically fall under the new regime. Conditions of use can be seen in the official guidance, but operators who are already using LSTs with VSOs under the existing trial must continue to follow trial rules (including the operator undertaking) until they choose to migrate. A transition period from 31 May to 30 November 2023 allows time for this migration. After this, any remaining VSOs will be revoked.
Legal Framework
LSTs fall under the provisions of the Road Traffic Act 1988, particularly:
- Section 41 – permits construction and use regulations, including length restrictions
- Section 42 – makes it an offence to contravene these rules
- Section 44 – allows certain exceptions, such as special type vehicles (LSTs), subject to conditions
The new statutory instrument formally amends the STGO 2003 order to add LSTs as a new vehicle category with its own governance (Article 57). As a result, these trailers must comply with various requirements apart from turning circle and length limits, which are now handled separately.
All other relevant regulations, such as the Road Vehicles (Authorised Weights) Regulations 1998, the Road Vehicles Lighting Regulations 1989 and the Goods Vehicles (Plating and Testing) Regulations 1988 continue to apply.
What is an LST?
An LST is a Longer Semi Trailer that exceeds the traditional 12.0m kingpin-to-rear length up to a maximum of 14.05m. No part of the trailer may project beyond a front swing radius of 2.040m from the kingpin.
The full dimensional limits are:
- Kingpin to rear of trailer: max 14.05m
- Loading area (parallel distance): max 15.65m
- Overall vehicle length (including tractor): max 18.55m
This additional space allows for up to four more UK pallets on a single deck, or up to eight more on a double deck — increasing total UK pallet capacity to a maximum of 60.
Weight, however, remains limited to 44 tonnes GVW on six axles. Because LSTs weigh more unladen, careful load planning is essential to avoid exceeding limits and risking enforcement penalties.
Construction Requirements
To comply, all LSTs must:
- Have 3 axles (with at least one being steerable)
- Include an on-board weighing device if GVW exceeds 38,000kg
- Ensure no rearward projection of load is present
Fortunately, many trailers already have bogie-based load sensing as part of the braking system, so often only a visual display is needed to meet this rule.
Trial History
The LST concept dates back to 2012, when a 10-year trial began with 1,800 trailers (900 at 14.6m and 900 at 15.65m). The trial was later extended in 2017 to allow a further 1,000 trailers and to run through until 2027.
Importantly, Gross Vehicle Weight limits were never increased under the trial — meaning many operators faced payload penalties due to higher unladen weight. Despite this, feedback was largely positive and formed the backbone of the now-permanent legalisation.
The official DfT consultation closed in February 2021, and the May 2023 announcement is the culmination of that review process.
Please visit our dedicated LST product page.
The full official guidance, which supports the new STGO Amendment, is linked below under Related Content.
