PMI Scheduling: How to Pick the Right Interval Without Guesswork
A preventative maintenance inspection (PMI) is a type of safety inspection that is carried out at pre-set intervals in line with what an operator has declared on the vehicle operator licensing service (VOL). The VOL records a time-based frequency for both vehicles and trailers.
Operators must ensure that safety inspections are carried out at the stated frequency as it is recorded on the VOL, and any changes intended to be made by licensed operators must be updated.
DVSA Guidance by Duty Type
An inspection frequency would normally range between four to thirteen weeks. The DVSA recommends ten to thirteen weeks for lightly loaded vehicles, six to ten weeks for general haulage, four to six weeks for arduous work, and four weeks for off-road vehicles.
| Operating Conditions | Frequency |
| Lightly loaded vehicles – easy operating conditions | 10-13 weeks |
| General haulage – trunking | 6-10 weeks |
| Arduous work – constant heavy loads | 4-6 weeks |
| Off road – difficult conditions | 4 weeks |
| Vehicle/trailer 12 years or older | 6 weeks |
Safety inspections should, where practical, be programmed to follow a time-based pattern like above. For example, a 2016 trailer used on quarry work would require a six week PMI.
Factors to Weigh
The frequency at which inspections are undertaken should be decided by assessing the level of mechanical deterioration likely to be incurred over a period due to the age of the vehicle, the type of work undertaken, the mileage covered, the operating conditions, and the load type.
Assessing these factors for each vehicle will, in most cases, enable a time-based programme of inspections to be formulated. Whatever the safety inspection interval is, its effectiveness in ensuring that the vehicle is safe for use on the road should be regularly monitored and proactively managed.
Six-Weekly Expectation
Older vehicles and trailers will need more frequent maintenance. As vehicles and trailers age, the average annual MOT failure rate increases, and they are more likely to experience in-service roadworthiness defects than newer vehicles. Therefore, guidance has reflected that older vehicles and trailers will need more frequent maintenance and has suggested a minimum safety inspection frequency of six weeks for vehicles and trailers aged twelve years and older.
How to Use ISO Weeks to Prevent “Creep”
Whichever safety inspection interval is chosen, the inspection frequency should not be extended without updating the VOL. The safety inspection should be carried up within the specified weekly or mileage-based time scale, and not beyond. To allow some flexibility in planning safety inspections, it is recommended that you use the International Organisation for Standardisation (ISO) week numbering system. Using this system ensures safety inspections are completed within the relevant ISO week it falls and prevents creep.
When and How to Update VOL if Intervals Change
The VOL records a time-based frequency for both vehicles and trailers. However, mileage-based inspection programs may be more suitable for some operators, if routes and workloads vary, but this will need to be linked to time. If you change your intervals – for example, because you adopt a mileage-based frequency – it is required that you update the VOL, entering into the system the expected maximum equivalent time-frequency of thirteen weeks. Then, you should ensure the mixed frequency box is ticked on VOL to record that a varied inspection is being used. You should use this same process if a mixed time frequency is being used for different vehicles or trailers on the fleet, and you should keep evidence that roadworthiness has not suffered.
It is sensible to monitor the effect of changing your inspection schedule on roadworthiness monthly. If an unacceptable increase in defects were seen, then a change back to the original schedule would be necessary.
Conclusion
You should use a maintenance scheduling system, planner, or wall chart to identify inspection dates at least six months in advance. We have an ISO-week PMI planner which you can download here.
On our website, you can also learn more about safety inspection intervals and how to set the right PMI interval.
You can stay in control with our intuitive job planner, giving you a real-time view of everything happening across your workshop in an easy-to-use calendar. You can set up recurring inspections like six-weekly PMIs, assign jobs, see technician availability, and track progress in real time. Learn more about job scheduling with Autocheck here.
