Saturday, April 10, 2010

Metal Roads

Barry, asked the question when he left a comment on my Country Roads post - "could your country roads be covered with metal?"

Why, yes, Barry, they could.  And are. 

 Metal waiting to be spread along our road

Rural, unsealed roads in New Zealand are called Metal Roads - because of the metal that is laid to compact them.  Imagine large stones taken from a riverbed or gravel pit, quarried to a regular size, then spread over a road surface that has been graded smooth.  The metal is compacted into the surface of the road by passing traffic and over time builds into a hard surface that does not become boggy when it rains.   Although we are experiencing something of a drought at the moment, believe you me, we do get a lot of rain in winter.

Right now dust and loose surface are a fact of life on our metal roads. Little can be done to combat this especially after such a hot and dry summer.

It can be quite difficult to drive on a metal road when it is first graded and more metal has been freshly spread.  My son compares it to driving on marbles and it can feel like that.  To me it always feels like I have a flat tyre and I invariably stop to check my tyres, although I know it is more likely to be the loose metal that is causing the car to be difficult to handle, especially on corners.  But traffic using the road gradually push the loosest bits of metal to the outside of the road, leaving a decent driving surface. You do not want to end up in "the loose" if you come upon another vehicle unexpectedly, especially if you are on the outside of a corner. That is what I call "a trap for young players" - because of the number of teenagers I have known to come to grief "in the loose".  However, it is my belief that young people who learn to drive on a metal road generally make good drivers.

Corrugations are one of the more bothersome aspects of unsealed roads. The Council’s contractor can grade out some of the corrugations but grading too deep can also affect the substructure of the road.  From my observations once corrugations appear in a stretch of road, they will re-appear again not long after being graded out.

The same goes for potholes which are common in damp weather where the road is too flat, or there is a hollow or corrugation. The traffic splashes the fines out and potholes develop. The grader driver tries to keep the roads shaped with a high camber for water to run off.  Along our road the main problem is on the approaches to the one lane bridges, where the timber or concrete of the bridge meets the road. Sometimes, you have to practically stop to negotiate on to the bridge without punishing your vehicle with an almighty thump.  

By their nature unsealed roads cannot be kept in a steady condition. Because they are made up of stones mixed with silt fines or clay, just how they hold together and last between grades is dependent on the weather and use.

Our roads services a farming district and carries heavy traffic such as stock trucks and milk tankers as well as tractors and farm vehicles although there is very little passing through traffic.  Most drivers we pass along the road use the road regularly and know its quirks. 

Our road has one novel aspect.  In a few places it runs alongside a creek with no fence or barrier between the road and the creek.  A wonderful incentive to drive carefully.


  1. In Derbyshire we call the same stuff Chatter, a mix of clay and graded stone. It's never used on listed roads, imagine the paint work on a Porche or Aston Martin. It is fun to drive on and good for young drivers, as is snow and ice. Accidents tend to be low speed.

  2. Metal interesting. At first I thought you were going to say something about them being paved with metal. Thanks for the description.

  3. Fascinating, Pauline. Amazing how different countries use their available resources differently to handle common problems.

    And now I know.

  4. My thinking was in line with Rebecca's. This was quite interesting to learn about.


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