WHAT’S GOING ON BETWEEN MIDDELBURG AND WONDERFONTEIN ON THE N4?
Always be alert, cautious and responsible when you take a steering wheel in your hands
Trans African Concessions’ engineering team continuously monitors all sections of the N4 Toll Route, evaluates traffic trends and investigates accidents along the entire route – in South Africa and Mozambique.
Following a spate of accidents recently, some concerns have been raised about the safety of the section between Middelburg and Wonderfontein.
TRAC’s engineers specifically investigated this section again, and publish their comment below.
Safe operating speeds
This particular section of road is a four lane undivided freeway, designed and constructed some 30 years ago, well before TRAC was granted the N4 toll concession in 1998.
Despite all engineering efforts and the best possible intentions, no road will ever be entirely safe to travel on. There is an inherent danger in driving on any road at any time in any conditions.
The speed limit on this section of road is 120km/h. Road users unrealistically expect driving conditions to be safe at all times when travelling at a speed of 120km/h. However, standards applicable to roads are laid down to control minimum requirements regarding stop-sight distances, horizontal curves, cross fall and super elevation, passing sight distances, etc under normal clear weather conditions, and at 120km/h.
Speed limits posted are indicative of the maximum legal operating speeds. These limits have, however, little to do with safe operating speeds. A good example would be for road users to slow down during misty conditions or when adverse weather conditions are experienced. Poor weather impacts negatively on safe driving, even with a speed restriction of 120km/h.
Take extra precaution during wet weather
A four lane undivided road is wider than a conventional 4 lane divided freeway.
As can be expected on any wide flat road surface during heavy rain storms – water flows over the road in a sheet. The wider the road and/or the heavier the rainfall, the thicker the sheet of water on the road surface will be.
The macro texture of the road surface (openings between the stone matrix of the riding surface) allows (to some extent) drainage of water on the road surface to the storm water side drains of the road. A course macro surface texture (achieved by certain surface applications) allows better flow conditions than others. This, however, is only beneficial with low intensity rain fall. With any intensive rain fall, the riding surface of the road cannot play a significant role and water will accumulate on the road surface.
Various factors impact on road safety during rain and may lead to aqua planning of vehicles
Furthermore, the formation of wheel rutting also impacts on road safety during heavy rain fall.
Rutting is caused by heavy vehicles and manifests itself as depressions in the surface under the wheel tracks. The ruts allow the flow or damming of water on the road surface.
Poor maintenance on drainage outlets can also cause ponds of water. Any of the above mentioned areas (where water accumulates) can cause of aqua planing if a vehicle hits the area at too high a speed.
It is most often the “surprise element” which causes drivers to lose control over their vehicles after hitting an unexpected pond of water.
The following factors can influence the collection of water on a road surface:
- Blocked drainage
- Wheel path rutting
- Change in road cross fall
- Longitudinal slopes
TRAC’s technical maintenance teams are constantly checking the road for signs of any of the above.
When vehicles travel too fast during rain storms, the following will happen
A tyre travelling through water gathers a wedge of water in front of it as the water is pushed aside. As the vehicle’s speed increases the wedge of water has less time to escape to the side or through the tyre treads.
The water at the leading edge becomes highly pressurized. When the pressure of the water exceeds the down force of the vehicle, the upward force (from the water) separates the tyre from the road surface. This results in a loss of traction, which could lead to accidents.
As explained above, during a heavy rain storm, the road surface cannot divert water quick enough away from the road. In these conditions, there are only two mechanisms which can assist to keep a vehicle safe:
- travel at a lower speed, and
- have tyres with a good tread which are correctly inflated.
Tyres with good tread are designed to disperse water from under the tyre and away from the tyre. This prevents the uplifting force resulting from the water.
Main causes of accidents on the N4 Toll Route
During 2010 the predominant causes of accidents were:
1. Tyre burst 15.5%
2. Lost control 14.9% (all incidents, including those where wet surfaces contributed)
3. Negligent driving 12.8%
4. Speed differential 11.3%
5. Falling asleep 10.8%
More than 78% of accidents in 2010 occurred during dry weather conditions. 19% of the accidents occurred during wet weather conditions.
The perception that the section of road between Middelburg and Wonderfontein results in more accidents is not supported by accident statistics.
The accident rate on this specific section of road between Middelburg and Wonderfontein has reduced since 2009. Accident statistics show an accident rate of about 0.5 accidents per million vehicle kilometres. This is less than the average of 0.6 accidents per million vehicle kilometres over the total length of the N4 Toll Route.
Check your tyres – it can save your life
On the 15th of December 2010, TRAC, in partnership with Arrive Alive and a tyre manufacturer conducted courtesy tests on tyres at the Alzu Petro Port near Wonderfontein. It was found that at least 50% of all tyres inspected were deflated or incorrectly inflated. 1 out 5 vehicles checked had worn tyres.
Deflated, incorrectly inflated and/or worn tyres all result in inadequate contact with the road surface during rain storms.
You too have a responsibility when you have the wheel in your hands
Negligent drivers travelling at high speeds and/or with badly maintained vehicles most often cause accidents on the N4 Toll Route.
In an on-going effort to monitor traffic conditions, TRAC records speed profiles in the slow and fast lanes of both carriage ways between Middelburg and Wonderfontein.
These records show that during 2010 on section N4/4 between the Fontein street interchange and the N11 (Hendrina) interchange, 15% of all the vehicles in the eastbound slow lane traveled at speeds greater than 122km/h and in the fast lane, faster than 132km/h – even during adverse weather conditions.
TRAC appeals to every road user to take individual responsibility and help adhere to safe and defensive driving practices. The company will continue to monitor road and traffic conditions and will intervene where required.
As part of TRAC’s standard upgrading and expansion programme, plans are underway to upgrade the first 10 kilometre section of road between Middelburg and Wonderfontein. Upgrading of the Wonderfontein to Belfast section was completed in 2009.
More information about this upgrade will follow shortly.
Get help from TRAC
For help and traffic updates on the N4 Toll Route call the TRAC Help Desk on 0800 8722 64 / 082 881 4444.
Issued: 28 February 2011
The Arrive Alive road safety website would like to confirm the importance of adapting driving to the driving conditions. Speed limits are merely a guide to the maximum speed allowed and there are many reasons why a lower speed and increased following distance should be applied for greater safety.
With the assistance of our Road Safety partner Trac N4 we have focused on some of these aspects on the Arrive Alive website. It was TracN4 who suggested that we also emphasize the dangers of driving in heavy mist as well as driving near veld fires. Along the N4 route these are some of the dangers unique to the area and we have developed and shared information about these unique threats on the road safety portal. The need for special care is also necessitated by unique South African risks when driving at night such as the threat posed by animals in the vicinity of the road.
There are however also other dangers impacting on the road surface itself – including the dangerous practise of overloading. Many vehicles are either not road worthy due to faulty tyre pressure – or are also overloaded. We would like to urge all vehicle owners and motorists to pay close attention to their own fitness to drive, to the roadworthiness of their vehicles and then, not only to obey the rules of the road, but also adjust their speed to the prevailing road conditions at the time….