Wednesday, December 05, 2012

Asphalt, Blacktop, Macadam: Let’s take a closer look



The SBT crew rides on all sorts of roads and we often find ourselves in neighborhoods and residential areas.  These deviations from the bike lanes along larger traffic arteries are a welcome change.  Residential areas provide much less traffic and it’s nice to not have the worry of being sideswiped.  A car collision is always possible but in a neighborhood the likely crash speed will be around 20 mph rather than 35-50 mph.    

This is not to say the idyllic neighborhood does not present its share of problems, it does.  The number one issue is with the road itself—the blacktop (or “Macadam,” named for its Scottish inventor, John Macadam in 1920, who first had the idea of binding small aggregate with tar in order to produce a smooth road surface).  We also call it asphalt while the English prefer “tarmac.”  Anyway, it has its problems: cracking, splitting, heaving and more.

Cracking is a huge problem with blacktop and it cracks in a variety of ways.  Most states, through their department of transportation, release manuals detailing asphalt problems and solutions and they have been kind enough to explain the types of cracking and their causes (your tax dollars at work).  Alligator cracking (left) is the most common, it occurs through age and use: the asphalt breaks into a spider web of small pieces.  Another method is longitudinal cracking caused by a poor joint or something shifting underneath the blacktop.  As riders we can roll over alligator cracking and pass on either side of longitudinal cracks with nothing more than some shaken giblets.  The blacktop issue bike riders need to be concerned with is transverse cracking, which are cracks that cross the roadway from left to right (and vice versa) and most often times trees are to blame and trees are common to almost every neighborhood.

When you are in a neighborhood be aware of the trees.  They may be affecting the roadway.  What we see of a tree above ground is exactly what is below ground.  So a tree with a 60-feet wide canopy above will have a 60-foot wide root system below and a limb that reaches out 30-feet into the air will have a root that reaches 30-feet underground and under the road way.  As that root grows it will push the blacktop up creating an anomaly of 3 to 6 inches and that is just enough to send you sailing over the handlebars when you didn’t see it coming.  This condition will only worsen with time and frost heaves in wintry climes.  When you ride among the trees have your eyes focused more intently on the road surface, have a good grip on the bars and slow it down a bit 

Last, be aware of “flushing” or “bleeding.”  This is a very common condition (right) when blacktop ages.  The road will appear shiny and glass-like.  In the summer the condition will make the surface sticky, in the winter slick.  In most cases the severe levels of flushing and bleeding will be in the “wheel path” of automobiles and with most bikers riding on the far side of roads this should not be too great of an issue but for roads that are underused and neglected this condition can overtake the entire surface.  Finally, “reveling” is the complete breakdown of the aggregate into cinders, avoid roads in this condition.  

The SBT crew enjoys riding and will ride almost anywhere, we just prefer to ride safely.  Please visit our website www.stickybottleteam.net.  Follow us on Twitter@SBTnetUSA. 

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