A truck can be travelling below the posted speed limit and still be moving too fast for the corner, its load or the conditions ahead.
That distinction is central to the 2026 National Truck Accident Research Centre (NTARC) Major Incident Investigation Report, which found the rate of major incidents attributed to inappropriate speed increased by 28.9% in 2025.
The findings challenge fleet operators to consider whether their approach to speed management adequately accounts for the changing dynamics of a working truck.
NTARC defines inappropriate speed as a situation where vehicle speed is incompatible with vehicle dynamics, road geometry or prevailing weather and road conditions.
“Importantly, this classification does not suggest the heavy vehicle was exceeding the posted speed limit,” the report states.
The consequences are often rollovers
Within the NTI insurance claims analysed, the inappropriate speed incident rate rose from 12.1 per 10,000 insured heavy vehicles in 2024 to 15.6 in 2025. This was the highest rate recorded across the report’s 2019–2025 analysis period.
Some 90.2% of incidents in this category involved only the insured heavy vehicle.
Rollovers were the most common outcome, accounting for 61.8% of inappropriate speed incidents. A further 17.3% involved the heavy vehicle running off the road.
For operators, that pattern puts the focus on how drivers select their speed before entering a curve or encountering a change in conditions.
The report notes that appropriate speed selection requires drivers to continually assess road curvature, surface conditions, weather, the mechanical state of the vehicle, combination type, load weight and load configuration.
A familiar road does not necessarily present the same driving task every day. A different trailer, a changed load or a wet surface can alter the margin available to negotiate it safely.
Low-speed roads also feature
Although 100 km/h zones accounted for the largest share of inappropriate speed incidents at 28.9%, more than a quarter—27.8%—occurred on roads with posted limits of 60 km/h or below.
Another 15% occurred in 80 km/h zones.
These figures describe the posted limits where incidents occurred, rather than the trucks’ actual travelling speeds. They nevertheless demonstrate that inappropriate speed incidents extend into lower-speed environments.
A fleet monitoring system that reports only breaches of posted limits could therefore leave an important part of speed-related risk unexamined.
The management question is whether the speed was appropriate for the vehicle’s circumstances at that point in the journey.
Articulated vehicles face a particular challenge
Articulated combinations recorded 28.8 inappropriate speed incidents per 10,000 insured vehicles in 2025, compared with 8.6 for rigid trucks.
Inappropriate speed accounted for 16% of all major incidents involving articulated combinations, compared with 9.5% for rigid vehicles.
The report discusses how centre of gravity, potential load movement and the articulation between prime mover and trailer can affect stability, particularly through curves or sudden manoeuvres.
These rates are measured per insured vehicle, rather than per kilometre travelled. Differences in operating exposure must therefore be considered when comparing vehicle types.
Even with that qualification, the findings provide a reason for operators to examine whether driver familiarisation and training sufficiently address the combinations and loads their fleet carries.
Regional routes deserve attention
Inner and outer regional areas together accounted for 67% of inappropriate speed incidents, compared with 47.9% of major incidents overall.
Major cities accounted for just 13.8% of inappropriate speed incidents.
The report identifies varying road geometry, changing speed environments and infrastructure conditions as potential challenges for drivers selecting an appropriate speed in regional and remote settings.
It also notes that advisory speed signage is often not designed with heavy vehicles in mind. Drivers must interpret the road ahead in the context of their particular vehicle and load.
For fleets, this supports closer attention to route familiarisation and the information drivers receive about curves, descents and other demanding sections of a journey.
Broader speed management
The practical implication is that speed management needs to include vehicle handling and operating conditions alongside posted-limit compliance.
Operators could use the findings to review how they communicate load characteristics, prepare drivers for unfamiliar combinations and identify challenging sections of regular routes. Where telematics or camera footage is available, it may help provide context for coaching and incident investigation, although this report does not establish the effectiveness of individual technologies.
The research also has limits. It covers NTI-insured major loss incidents exceeding $50,000, and changes to data collection and validation in 2025–2026 may affect comparisons with earlier years. Each incident receives a single dominant cause code, which cannot capture every contributing circumstance.
For fleet managers, the central question remains practical: does the organisation know when a compliant speed could still be unsafe for the truck doing the job?
