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[Bigmikelakers]

What are the lifespan of roads? I mean like overpasses, ramps, bridges, etc? I know long span bridges have life spans. But what about highways in general? Here in Socal some overpasses have the date stamped on the overpass columns. The 405 overpass near my house is dated 1964. Nearly 50 years old. Is there going to be a point in time in the next 10-20 years where more and more roads begin to collapse since there will be a large sum of roads 50-70 years old?

[vtk]

What are the lifespan of roads? I mean like overpasses, ramps, bridges, etc? I know long span bridges have life spans. But what about highways in general? Here in Socal some overpasses have the date stamped on the overpass columns. The 405 overpass near my house is dated 1964. Nearly 50 years old. Is there going to be a point in time in the next 10-20 years where more and more roads begin to collapse since there will be a large sum of roads 50-70 years old?

Hopefully the DOTs will be able to replace bridges before they collapse.  However, different bridges may have different life spans (compare the Broolyn Bridge to the Tappan Zee) and even thoough there was a construction boom in the mid-20th century, that doesn't mean everything was built all at once.  Many smaller bridges from that era have already been replaced as part of capacity improvement projects.

As for non-bridge portions of roads, they are usually reconstructed from the grouund up, on a cycle of 30–50 years, or when the highway's geometry is modified such as to improve safety or capacity.

[Scott5114]

It also depends on the soil, the materials used, the amount of use, and the type of use.  Asphalt is usually cheaper but it will usually wear out faster than concrete.

Obviously, busy bridges will need to be replaced sooner because they will need more capacity. There is a one lane bridge built as a railroad bridge in 1896 or so in rural Oklahoma that is still in use today. The only major work done on it was to replace the wood deck with concrete because some moron torched the old deck. It still performs admirably because the traffic counts are light, the bridge is still strong, and one lane is all that is needed.

The amount of truck traffic a road receives will also dictate its lifespan. A road with a lot of trucks is abused more than one that is used by mostly cars and thus will wear out faster than a quiet one or one with little truck traffic.

[J N Winkler]

Roads and bridges are designed with defined useful lives but the extent to which they last, as Scott notes, depends hugely on individual circumstances.  Some roads don't last as long as their design lives while some outlast them several times over.

I don't have specific information on US practice, but in Britain design codes currently in use call for a design life of 40 years for the road and 120 years for the bridge.  There is no clear economic argument in favor of using one-size-fits-all design lives for highway infrastructure, but I suspect that in most cases, in most US states, the nominal design life for road bridges is significantly longer than that used for the roadbed.  This is because when a road fails, the main consequences are primarily economic, while if a bridge fails, people can lose their lives.

A key consideration, when choosing a design life for a piece of highway infrastructure in a corridor which is expected to remain in use well beyond any reasonable choice of design life for the actual physical fabric, is rollover costs.  What will need to be done when the highway comes to the end of its natural life and how much will that cost?  In the case of rural Interstates which are considered unlikely to need widening ever, for example, it is often economic to design for 40 years or even longer, while for a highway which is likely to need widening within a few decades, a shorter design life of 20 to 25 years may be more appropriate.  This is where sensitivity testing has to be done as part of the cost-benefit analysis--the owning agency has to know how the results change for various possible choices of design life.  Frequently agencies also compute costs and benefits for diverging scenarios of traffic growth.  In Spain, for example, proyectos de construcción report design-year traffic estimates in terms of low growth, medium growth, and high growth, and report design-year LOS for each scenario.

[2Co5_14]

I had a chance to do bridge inspections during one of my paid college internships, so I've seen some serious deterioration (flaking off slabs of rust until I could see holes in the steel beams!)
 
Most bridges in the US are inspected at least every 2 years, and ones with documented issues are done more frequently.  I know the Georgia DOT (and all the other states I assume) have a database of all their bridges and prioritize repairs of the ones in the worst condition.  A bridge may be rated "structurally deficient" and still be safe for the public, but if one is discovered to be in danger of possible failure, it is closed immediately.

As far as the average life span of a typical concrete or steel highway bridge, I've seen figures ranging from 50 to 100 years, with the majority in the 70 to 80 year range.  I'm working on a bridge project right now to replace a minor state highway bridge built in 1953 - it will be about 2015 before the actual work is done.

[ctsignguy]

Sometimes, material deteriorates faster than expected. Several years ago, when I-670 was being rebuilt just north of Downtown Columbus (it used to be a part of I-71 many years ago), there was a brideg over Neil Ave that was needing replaced. Well, i recall reading the construction company allotted two weeks to take it down....but when they started demolition, they found the steel and concrete were so badly deteriorated that the concrete was all but powder....

the bridge was down within 2 days....

[SteveG1988]

It all depends on the care taken to preserve the span, Between Trenton NJ and Morrisville PA stands a 1884 built pin connected truss bridge, there are several ones like it built in the 1900s north of that point, it just underwent a complete overhaul, repainted, replacing any worn part, etc. It still has a 3 ton weight limit, but is safe. There are still late 1700s bridges in use around new jersey that carry road traffic. Whreas out near the ocean we have a freeway bridge built in the 1950s for the parkway that is having severe deteoriation issues due to the salt air. Next to that bridge is a very badly maintained, the beesleys point bridge, span which is closed to all traffic and is rusting away in the same conditions. All of these spans are owned by different state/local/bi state authorities, and each one is maintained differently.

[roadfro]

As JN Winkler noted, pavements and bridges are typically designed to a desired or expected design or service life. I seem to recall from a pavements class I took several years ago that 30 years is a pretty average service life for pavements in the US. That number of course varies depending on roadway classification and several other factors; 40 years or more may be more typical for Interstate highways in rural areas and some other applications. I seem to recall 50 years now being a typical base design life for most types of bridges, although going higher like to 70 years is not incredibly uncommon (where budgets and other design considerations can accommodate).

One consideration as far as asphalt pavements is concerned is the maintenance cycle. Since asphalt is a flexible pavement, it loses structural integrity over time. However, not the entire pavement loses its strength. Thus, the design life cycle of an AC pavement typically takes into account preventative and rehabilitative maintenance--slurry seals, overlays, "mill & fill", etc.--performed periodically throughout the life cycle until the underlying base and sub-base material is expected to fail near the end of service life period and a complete reconstruction is required. All this to say that an overlay doesn't mean the pavement is at the end of useful service life, but it's factored in from the beginning.


Going back to one of the OP's points. One of the problems facing the US currently is that we're getting to (or already at, in many areas) the point where many of our nation's bridges are nearing the end of design life. A good chunk of this is due in large part to the Interstate highway building boom in the 50s-60s or so, with many bridges of that era being designed for 40-50 year life spans. In many cases, such bridges are still functioning and safe, but may have weight limits or other restrictions in order to help extend their useful service beyond intended design.