Aug 10, 2012
Variable speed limits not always effective, study showsBack
Stellenbosch University|Transport|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 inter- action 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 crumple 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 regarded 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 being 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 database (such as the speed-over-distance camera) is 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 differ- ences 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 acci- dent 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 the 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 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.
Edited by: Martin Zhuwakinyu© Reuse this Comment Guidelines
Other Automotive News
Updated 12 minutes ago The extensive compliance processes instilled to regulate the manufacturing of the set-top boxes (STBs) required for South Africa’s migration to digital terrestrial television (DTT) have emerged as a serious weakness as industry gears up for the imminent and...
Updated 42 minutes ago Honda has unveiled the newest version of Asimo, its advanced humanoid robot, now featuring the ability to communicate in sign language and climb stairs without stopping. Asimo, which stands for Advanced Step in Innovative Mobility, was first introduced 14 years ago....
Updated 53 minutes ago Department of Public Enterprises (DPE) director-general Tshediso Matona confirms that the interdepartmental task team established to find a solution to Eskom’s financial problems has agreed that further support will be required. However, he says it is premature to...
Recent Research Reports
Steel 2014: A review of South Africa's steel sector (PDF Report)
Creamer Media’s Steel 2014 report provides an overview of 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 steel and stainless...
Projects in Progress 2014 - First Edition (PDF Report)
This publication contains insight into progress at the delayed Medupi and Kusile coal-fired projects, in Mpumalanga and Limpopo respectively, as well as at the Ingula pumped-storage scheme, which is under construction on the border between the Free State and...
Automotive 2014: A review of South Africa's automotive sector (PDF Report)
The report provides insight into the business environment, the key participants in the sector, local construction demand, geographic diversification, competition within the sector, corporate activity, skills, safety, environmental considerations and the challenges...
Construction 2014: A review of South Africa's construction sector (PDF Report)
Construction data released during 2013 hints at a halt to the decline in the industry during the last few years, with some commentators averring that the industry could be poised for recovery. However, others have urged caution, noting that the prospects for a...
Electricity 2014: A Review of South Africa's Electricity Sector (PDF Report)
This report provides an overview of the state of electricity generation and transmission in South Africa and examines electricity planning, investment in generation capacity, electricity tariffs, the role of independent power producers and demand-focused initiatives,...
Defence 2013: A review of South Africa's defence industry (PDF Report)
Creamer Media’s 2013 Defence Report examines South Africa’s defence industry, with particular focus on the key players in the sector, the innovations that have come out of the defence sector, local and export demand, South Africa’s controversial...
This Week's Magazine
The Electronic Systems Laboratory (ESL) of the Department of Electrical and Electronic Engineering at Stellenbosch University is strongly reaffirming its position as one of South Africa’s leading centres for satellite technology and expertise. It is currently...
The world’s lowest-cost diesel-electric locomotive is not made in China, but in Pretoria, at RRL Grindrod Locomotives’ newly upgraded 30 000 m2 plant. The company’s locomotive pricing is “more competitive than any other original-equipment manufacturer (OEM)...
The South African Defence Review 2012, released to the public at the end of last month (despite the year given in its title) recommends the creation of the post of Chief Defence Scientist. This official would be responsible for the management of defence technology...
AltX-listed engineering technology company Ansys has been awarded an R188-million contract by Transnet to supply integrated dashboard display systems to the freight rail utility’s locomotives. Black-owned and controlled Ansys developed the bespoke integrated system...
South Africa’s sole nuclear power station Koeberg, which is located in the Western Cape, breached a major operations milestone on April 4, which marked the thirtieth anniversary of Unit 1 having been connected to the grid. Eskom, which operates the two-unit plant,...