Regular road maintenace

How often should a road be completely resurfaced?  What criteria should be used to decide whether to repair damaged surfaces or not, and whether to resurface the whole road?  Interesting questions for operational research. 

Devon has an extensive network of roads, from the motorway (M5) through dual carriageways to minor roads which run through quiet parts of the county.  Each one needs to be cared for.  Finance for the repairs is limited, though it comes from different sources, depending on the importance (load) of the traffic on that road.

Tina and I were walking in South Devon last week.  To get to the starting point we used several minor roads, and part of our walk took in a mile or so of single track roads.

We joke that we enjoy driving on roads where there is grass growing in the centre, a consequence of the fact that the centre of the road is never touched by the wheels of vehicles in such roads. However, one consequence of the growth of vegetation is that the road surface is damaged by the roots.  The surface is also affected by the water which runs off to the road-side. 

In the walk, we noticed a contrast between the minor roads that run through woodland and those that run through farm fields, with hedges or fences.  The latter dry out much more quickly than the former, as they catch the sun.  But, more significantly, any debris on the road surfaces dries and can blow away; it doesn't accumulate.  On the other hand, minor roads in woodland accumulate wet woody debris which doesn't dry out; and then water running off these roads is forced into the road-side where it erodes the surface. 

So, thinking of these observations made me consider those questions of repair or resurfacing, especially for those single-track minor roads.  I suspect that the answer is that nobody has models for it, and work is simply carried out on the basis of inspections and reports from road users.  But there is a student project here for someone.


  1. This post strikes home for me. I live in East Lansing, Michigan, the home of Michigan State University and a suburb of the state capitol. Our roads are the envy of two, possibly three, third world countries. The local traffic engineer maintains a report classifying roads into one of four or five categories, anywhere from nearly pristine to in dire need of repair. He also has a formula or model of some kind for prioritizing maintenance and repairs, although I doubt it is anything as sophisticated as an optimization model.

    Unsurprisingly, it is considerably cheaper to perform modest maintenance on a road in fairly good condition (the second or third best category) than to repair a significantly damaged road (fourth or fifth categories). So priority goes to the former, and once a road deteriorates sufficiently it goes untended (other than perhaps an occasional "hot patch" to potholes that have been reclassified as craters). Theoretically, the category 5 roads will be repaired someday, but apparently the engineer's model does not predict in which millennium that will occur.

    There's an interesting optimization problem to be sorted out here, the hardest part of which is parameterizing the objective function. Repair costs can be estimated with reasonable accuracy, but what is the cost to the city of damaged roads? How many passenger miles on a somewhat bumpy road equate to one passenger mile on a road that appears to have been carpet-bombed?


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