The Department for Transport (DfT) has formally approved the use of Longer Semi Trailers (LSTs) for general operation on UK roads. This follows a press release earlier in the month confirming that legislation would be introduced on 10 May, enabling the vehicles to enter service from 31 May.
Many operators expected the change to simply increase the existing trailer length limits by 2.05m so that LSTs could operate under the same framework as standard 13.7m trailers. Instead, the regulatory approach is different.
The existing Road Vehicles (Construction and Use) Regulations 1986 remain unchanged. Rather than altering those limits, LSTs have been introduced as a new trailer category through the Road Vehicles (Authorisation of Special Types) (General) Order 2023 (No. 524), commonly known as STGO. This creates a separate statutory framework with specific operating conditions.
Operating requirements
Operators intending to use LSTs must comply with a number of legal requirements under the new regime:
- Route plans and risk assessments must be prepared for each route, including diversionary routes.
- Copies of route plans and risk assessments must be carried in the towing vehicle and retained for two years.
- Operators must pre-notify the Secretary of State of their intention to operate LSTs using the Vehicle Operator Licensing (VOL) system. This requirement will apply for an initial five-year period.
In addition to the statutory requirements, the official guidance also covers operational best practice relating to:
- Driver training and scheduling
- Record keeping
- Training for transport managers and other key staff
- Safe and appropriate loading practices
LSTs entering service from the implementation date automatically fall under the new regulatory framework. However, operators currently running LSTs under Vehicle Special Orders (VSOs) as part of the original trial must continue to comply with the trial rules, including the operator undertaking, until they choose to migrate to the new regime.
A transition period from 31 May to 30 November 2023 has been provided to allow this migration. After that date, any remaining VSOs will be revoked.
Legal framework
The operation of LSTs ultimately sits within the wider provisions of the Road Traffic Act 1988, including:
- Section 41 – allows regulations governing construction and use, including vehicle dimensions.
- Section 42 – makes it an offence to contravene those regulations.
- Section 44 – permits exceptions for special type vehicles subject to defined conditions.
The new statutory instrument amends the STGO 2003 order to add LSTs as a dedicated vehicle category under Article 57. Turning circle and length limits are therefore managed through this special-type classification rather than through the standard Construction and Use framework.
All other relevant legislation continues to apply, including the Road Vehicles (Authorised Weights) Regulations 1998, the Road Vehicles Lighting Regulations 1989 and the Goods Vehicles (Plating and Testing) Regulations 1988.
What is an LST?
An LST is a Longer Semi Trailer that exceeds the traditional 12.0m kingpin-to-rear length limit 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 dimensional limits are:
- Kingpin to rear of trailer: maximum 14.05m
- Loading area (parallel distance): maximum 15.65m
- Overall vehicle length including tractor unit: maximum 18.55m
The additional length allows operators to carry up to four additional UK pallets on a single deck trailer, or up to eight additional pallets on a double-deck configuration. This increases maximum pallet capacity to around 60 UK pallets.
Gross vehicle weight limits remain unchanged at 44 tonnes GVW on six axles. Because LSTs are typically heavier unladen than standard trailers, operators must carefully plan loads to avoid exceeding axle or gross weight limits.
Construction requirements
To comply with the new rules, LSTs must meet several construction requirements:
- The trailer must have three axles, with at least one steerable axle.
- An on-board weighing device is required where the gross vehicle weight exceeds 38,000kg.
- No rearward projection of load is permitted.
Many modern trailers already include bogie-based load sensing systems as part of their braking control architecture. In many cases, only a driver-visible display is required to meet the weighing device requirement.
Trial history
The LST programme began in 2012 with a ten-year government trial involving 1,800 trailers: 900 units at 14.6m and 900 units at 15.65m. In 2017 the trial was extended with an additional 1,000 trailers and the trial period was extended to run until 2027.
During the trial, gross vehicle weight limits were never increased. As a result, some operators experienced reduced payload capacity due to the higher unladen weight of the longer trailers. Despite this limitation, operational feedback was broadly positive and informed the government's decision to proceed with permanent legalisation.
The DfT consultation on the future of LSTs closed in February 2021, with the May 2023 legislation completing the process.
Further details about the vehicle type can be found on the LST product page. The official guidance supporting the STGO amendment is also available through the related resources.
