VEHICLE OVERLOADING CONTROL – ECONOMIC, ENGINEERING AND OPERATIONAL CONSIDERATIONS

The economics of it all

Africa’s transport sector is critical for the continent’s social and economic prosperity but is falling desperately short of requirements.   The World Bank estimates that over USD200 billion of Africa’s trade is carried by the trunk road network between economic hubs and major seaports.  Less than 30% of this network is paved, and only about half the paved roads are in good condition.

The African Development Bank estimates that US$130-170 billion is needed annually to support Africa’s infrastructure requirements.  Transportation projects will need one-fourth of this amount, and 80% of this money will be spent on maintenance and rehabilitation.  Several project development and financing models are being implemented to bridge the gap, including Toll-Operate-Transfer (TOT) models, co-financing between governments and development agencies and Public-Private Partnerships (PPPs).  The capital investments are invariably huge and must therefore be protected.  The risks and time-based costs of vehicle overloading are not always included in economic evaluations and can have a profound effect on the project life-cycle costs.

According to the Office of the Special Advisor on Africa of the United Nations, approximately 60 percent of the continent’s population lacks access to modern infrastructure, which isolates communities, prevents access to health care, education and jobs, and impedes economic growth. Inadequate infrastructure is a major deterrent for Africa to achieve its full growth potential. Hence, meeting the demand for key infrastructure, both physical and social, is a priority area for the countries in the region.
EXIM Bank, Working Paper No 72, March 2018

The engineering realities

The structural effects of overloading:

By far the largest risk is the damage done to a road pavement by vehicle loads and the resulting impact on road maintenance costs.   The effects of overloading have been researched extensively over the years and are well documented: a single axle overloaded to twice the legal limit will do as much damage as 18 legal axles.  For shallow pavement structures (for example, on secondary- and inner-city roads) the damage could be 3 times as much.  The extent (proportion of overloaded vehicles) and degree (excess over the legal limit) of overloading profoundly affects the life-cycle cost of a road pavement and could potentially destroy the business case for an investor, road owner or concessionaire.

Overloading that goes unchecked and uncontrolled has a commercial, economic and societal impact.  For the investor, road owner or concessionaire, the business of owning and maintaining a road is negatively impacted, and the service to road users is impaired.  For society and the economy, there is the added cost of damage to goods and vehicles, injury, loss of life & income and higher vehicle running costs.  The total adverse impact of overloading compounds over time and is not immediately evident.

Safety considerations:

Overloading places people, goods, livestock and vehicles at risk.  An illegally loaded truck causes greater damage to its tyres, suspension, drive train and braking system.  On roads with steep gradients and sharp turns the risk increases dramatically, and the resulting costs of injuries, death and damage to goods and vehicles are often overlooked.

Vehicle operating costs:

Deteriorating roads are more expensive to drive on.  Predictive models for heavy vehicles suggest that total vehicle operating costs could be 30% higher when moving from good to poorer road surfaces.  The journey takes longer, fuel consumption is higher and wear-and-tear increases.  These effects are more pronounced for overloaded trucks, a fact to which hauliers are often oblivious – there is a revenue benefit from carrying more payload, but the incremental costs are delayed.

The technology and operational requirements

To measure is to know – information about the extent and degree of overloading is critical in the design of overloading control strategies and the planning for road maintenance requirements.  A road pavement structure is designed to carry a cumulative number of (equivalent) 80kN axles over its life.  If actual loads are in excess of the design specifications, maintenance requirements increase and pavement life is shortened, with adverse economic impacts – not to mention the indirect economic costs discussed above.

Vehicle weighing technologies are available in many shapes and configurations to suit the application:

Portable scales allow the truck owner or road agency to weigh a truck anywhere and on any surface.  Data capturing and processing technologies have advanced in recent years and a full scope of weighing statistics are produced instantaneously.  The convenience, mobility and cost of this technology are its largest advantages even if accuracy deteriorates with frequent assembly and dismantling, requiring calibration.

Permanent roadside scales use a steel or Qconcrete deck supported by a load cell system.  Trucks are weighed stationary and the management software produces axle loads and gross vehicle weight by taking account of vehicle classification and axle configuration.  Permanent scales and their related roadside buildings and road infrastructure are expensive to build and maintain, but they are durable and with proper calibration and upkeep are effective ways of weighing and apprehending overloaded vehicles.

Weigh-in-motion (WIM) scales strike a balance between portable and static systems.  They comprise of a pad- or strip sensor in one or both wheel tracks and use bending plate, capacitive or piezo-electric sensors to convert the impact of a passing wheel to a weight, and algorithms to produce complete vehicle loading statistics.  WIM scales are often deployed along with electro-magnetic induction loops to provide continuous data about traffic and axle loads.

On-board scales are gaining in prominence.  Load cells installed on a truck chassis, or readings from air suspensions, provide data about loaded weight that allows the trucker to maximise payloads and avoid the penalties of overloading.  Even if expensive, the convenience and time savings of being able to weigh at a loading site are key factors in the popularity of this technology.  On-board scales are also potentially an effective tool in self-regulation schemes.

These weighing technologies all have their respective places and functions and are often used in combinations.  For example, a WIM installation is used to screen heavy vehicles and alert law enforcement officials to perform a static check at the next permanent station.  This deployment is used successfully at toll gates, where WIM sensors are placed near the entrance of the plaza and a permanent weighing station immediately downstream.

The lessons and insights

Our experience in the vehicle weighing business taught us that a number of factors will determine the success of an overloading control project, during conceptualization, design and operation phases.  We are also of the view that the ongoing advances in information and communications technologies can produce a step-change in the effectiveness of overloading control strategies.

 1. WIM placement and operation:

An effective WIM installation requires a careful selection of location, and installation in compliance with the road agency’s or manufacturer’s technical guidelines.  A rougher road section that activates too much suspension movement is unsuitable.  Vertical gradients beyond a minimum should be avoided too.  Roadside installation of the data capturing and communications devices must be tamper-proof, and so on.

 2. Permanent scales:

Besides careful design of the ergonomics and geometric layouts of the facility, a good operational plan will promote efficiency and effectiveness: weighing stations are the interface between operations and law enforcement, and the business processes that regulate interactions must be managed carefully.  For example, how is an overloaded vehicle processed?  How should the offending cargo (goods and people) be treated?  Is the statutory fine for an overloaded vehicle a sufficient penalty?

Given the incentive to overload, bribes and threats are not uncommon at these stations.  Measures to detect and apprehend offenders, protect personnel and safeguard facilities and equipment are important elements of the design and operational considerations.

 3. Industry self-regulation:

It is in the best interest of all parties to encourage ownership and self-regulation of the freight industry and this should be part of an overloading control strategy.  In South Africa, the SA National Road Agency (SANRAL) implemented a Road Transport Management System (RTMS), an industry-led self-regulation scheme, that encourages consignees, consignors and transport operators to implement measures to preserve road infrastructure, improve road safety and increase productivity.  The scheme supports the SA Department of Transport’s National Freight Logistics Strategy and is led by industry associations and government agencies (see www.arrivealive.co.za for detail about South African road freight legislation and control of overloading).

 4. Interoperability and data integrity:

The primary objectives of an overloading control strategy are to protect the investment in infrastructure, improve road safety and enhance economic activity.  Weighing installations on a road network, both permanent and WIM stations, should ideally be integrated into a system that will (a) produce a network-wide view of overloading occurrences and trends, and (b) support efforts to encourage compliance, apprehend offenders and prosecute them.

A permanent weighing station on a tolled road is easily avoided by overloaded trucks if WIM or semi-permanent stations are not strategically placed on alternative routes.  The ability of outlying and permanent stations to share alerts with each other and with law enforcement is a critical piece of the management system.

Information and communications technology makes it possible for data streams from individual stations to be transmitted, processed, stored and produced on a real-time dashboard.  The integration of data from traffic counting stations, weighing stations and toll plazas, now with the benefit of video streaming, cloud computing, data analytics and artificial intelligence, will support the road agency’s need to maintain a near-term perspective of the traffic events and patterns that are affecting the network, of the state of functioning of counting, weighing and measuring equipment, and of the impact of law enforcement.

Importantly, the identification and prosecution of offenders will be compromised if information in the national vehicle register is deficient, not accurate, or not shared.  In many countries the agencies responsible for ownership, operations, maintenance, safety and compliance functions on the public road network act in isolation, using IT platforms that were designed for different purposes.  The good news is that disparate data bases need not be an obstacle, because integration solutions are available and becoming ever more effective and affordable – the challenge is not technology, but the willingness to engage and produce a solution.   

While overloading control on a road network is a critical part of solving the infrastructure investment challenge, weighing trucks and counting vehicles are small pieces of the puzzle.   Combining all the parts into a systems solution to manage and protect the whole, is the key to an effective strategy to protect the substantial capital investments that are (and will still have to be) made in Africa’s road infrastructure.

(Text produced by Jurie Lombard, Hannes van Wyk and Hennie du Plessis)

For further reading about his topic, please see here