Jul 19, 2012
No use for truck, bus speed limits if not enforced, says research studyBack
Engineering|Pretoria|Road|Roads|Safety|Trucks|United States|University Of Stellenbosch|Western Cape|Christo Bester|Electronic Stability Control
© Reuse this
In 1999, following a fatal bus collision involving British tourists, the then Minister of Transport reduced the maximum speed limit for public transport vehicles (buses and minibus taxis) to 100 km/h. Heavy vehicles were already limited to 80 km/h.
SU civil engineering professor Christo Bester says there are a number of safety-related reasons why different speed limits could be applied to different types of vehicle.
For example, because of the differences in mass, different vehicles have different stopping distances. And, related to the interaction between the tyres and the road surface, is the ability of a vehicle to negotiate a horizontal curve. Excessive speeds can lead to a vehicle slipping, or overturning on a sharp curve.
Different vehicles also have different safety features, such as crumble zones, passenger restraints and electronic stability control.
However, despite these benefits, the application of variable speed limits is not without problems, with the most important of these being the ability to effectively enforce different limits on the same road, says Bester.
Variable speed limits are only viewed as effective when 85% of drivers keep to the designated limit. However, from studies carried out in the Eastern and Western Cape, 60% of minibus taxis did not comply with the speed limit, with the same true for 64% of heavy goods vehicles.
Bester says automatic speed cameras cannot differentiate between vehicle types, which is why only the highest limit can be enforced.
Speed cameras that are manually operated, or sophisticated apparatus with access to the South African vehicle data base (such as the speed-over-distance camera) are necessary.
“It is clear, however,” emphasises Bester, “that minibus taxis and heavy vehicles do not adhere to their maximum speed limits. It is clear that these [variable speed] limits should be reconsidered or at least enforced on a larger scale than is currently the case. If the limits are not enforced, there is clearly no justification for having them.”
Bester also questions why legislation regarding the 80 km/h speed limit refers to heavy goods vehicles only.
“Why allow a higher speed limit for buses than for other heavy vehicles? Or vice versa – why force drivers of heavy goods vehicles to travel slower than heavy passenger vehicles?
“Some reason that the value of time is higher for passengers than it is for freight and, therefore, buses should be allowed higher speeds, but this is an economic decision and not one that relates to safety – the main reason given for speed limits. Economic decisions regarding vehicle travel should be taken by operators and not legislators.”
Another problem is that international research has shown that increased differences in speed also result in higher crash rates, as faster and slower drivers have to be accommodated in the same road space. Particularly in two-lane, two-way roads, differentiated speed limits can result in reckless driving behaviour.
Bester says research has shown that the chance of being involved in a road accident is lowest when the vehicle is travelling around the average speed of the surrounding traffic.
In the end, argues Bester, there is no reliable evidence of the safety benefits of variable speed limits. However, there is a concern that by increasing speed variance, differential speed limits may increase overall accident rates.
“This is a solid argument against a differentiated speed limit between heavy vehicles and other road vehicles, and in favour of a standard speed limit for all vehicles.”
Bester then also suggests the more effective enforcement of reconsidered variable speed limits, or the introduction of a lower maximum speed limit for all vehicles, as proposed by the former Minister of Transport, as well as the further reduction of maximum speed limits on single lane roads, in line with international practice.
* Professor Christo Bester and US student MS Marais presented their research at the recent Southern African Transport Conference, held in Pretoria.
Edited by: Creamer Media Reporter© Reuse this Comment Guidelines (150 word limit)
Other Roads News
Updated 31 minutes ago The “robust” inverse relationship between the rate of unemployment and housing prices continues to confirm that the average price of homes is largely driven by the performance of the local economy, the latest ‘Rode’s Report on the South African Property Market’ has...
Updated 1 hour 12 minutes ago National carrier South African Airways (SAA) has been welcomed as a member of the Roundtable on Sustainable Biomaterials (RSB), the Swiss-based international multistakeholder initiative focused on biomass and biomaterial production and processing sustainability. The...
Updated 1 hour 33 minutes ago The scene of a train collision in Johannesburg will take about six hours to clear, Prasa CEO Mosenngwa Mofi said on Tuesday. At least one person, a female safety officer, was killed when the two trains collided at Denver station, Mofi said.
Recent Research Reports
Steel 2015: A review of South Africa's steel sector (PDF Report)
Creamer Media’s Steel 2015 report provides an overview of the key developments in the global steel industry and particularly of South Africa’s steel sector over the past year, including details of production and consumption, as well as the country's primary carbon...
Projects in Progress 2015 - First Edition (PDF Report)
In fact, this edition of Creamer Media’s Projects in Progress 2015 supplement tracks developments taking place under the Renewable Energy Independent Power Producer Procurement Programme, which has had four bidding rounds. It appears to remain a shining light on the...
Electricity 2015: A review of South Africa's electricity sector (PDF Report)
Creamer Media’s Electricity 2015 report provides an overview of State-owned power utility Eskom and independent power producers, as well as electricity planning, transmission, distribution and the theft thereof, besides other issues.
Construction 2015: A review of South Africa’s construction sector (PDF Report)
Creamer Media’s Construction 2015 Report examines South Africa’s construction industry over the past 12 months. The report provides insight into the business environment; the key participants in the sector; local construction demand; geographic diversification;...
Liquid Fuels 2014 - A review of South Africa's Liquid Fuels sector (PDF Report)
Creamer Media’s Liquid Fuels 2014 Report examines these issues, focusing on the business environment, oil and gas exploration, the country’s feedstock supplies, the development of South Africa’s biofuels industry, fuel pricing, competition in the sector, the...
Water 2014: A review of South Africa's water sector (PDF Report)
Creamer Media’s Water 2014 report considers the aforementioned issues, not only in the South African context, but also in the African and global context, and examines the issues of water and sanitation, water quality and the demand for water, among others.
This Week's Magazine
Forest products group Sappi has confirmed the selection of its 25 MW biomass-to-power project, to be erected at its Ngodwana mill, in Mpumalanga, as a preferred bidder under the South African government’s Renewable Energy Independent Power Producer Procurement...
Information and communications technology (ICT) distributor DCC is making Windows- and Android-operating systems tablets available through retailers and education equipment suppliers to provide school children with affordable, high-performance education tools. The...
Another cement manufacturer is set to enter the Ugandan market, raising hopes that prices will come down and spur growth in the construction industry. National Cement, a Kenyan manufacturer, has unveiled plans to invest $195-million in a new manufacturing plant in...
With growth rates exceeding that in the developed world – at an average of between 4% and 5% between 2002 and 2014 – African countries provide investors with ample reason to tap into booming consumer demand says Manufacturing Circle executive director Coenraad...
The South African Chamber of Commerce and Industry’s (Sacci’s) Business Confidence Index (BCI) decreased by 3.7 index points month-on-month to 89.1 in March.