How long would it take for a motorway to disappear?

[kyser_soze]

Decades. It'd be unusable for high speed, but probably still drivable for ages, and will remain a landscape feature for centuries. Even the most humble road goes down about 2-3 feet in terms of shingle underlay etc etc - m-ways are even deeper.

 

[dilute micro]

Saw the show again last night. I realized I totally missed the part about the nuclear power plant meltdowns in the first few weeks without power. Basically the whole northern hemisphere would be a radioactive wasteland. It's scary how we're so dependent on electricity.

 

[Johnny Canuck3]

Abandoned highway, northern Manitoba

 

[Johnny Canuck3]

 

[cesare]

Depends where it is.

 

[Roadkill]

Given that there are a fair few abandoned runways from World War II airbases that are still usable, if a bit overgrown these days, I think it'd be a matter of decades before a motorway decayed so far as to be impassable, and it'd remain as a landscape feature for centuries, albeit becoming increasingly broken and overgrown as time passed.

 

[kyser_soze]

In fairness, I'd be prepared to offer money that the USAF built it's runways to land B-52s and C-5 Galaxies to a higher standard then HMG builds the roads (well, until recently - new roads like the resurfaced bit of the M-40 and the M-6 toll road feel like driving in France...)

 

[Roadkill]

I'm not sure about that. A lot of those bases were thrown up in a hurry...

 

[Psychonaut]

I can still see the black/white paint on the kerbstones from WW2. Only just though - im sure there was more 10 yrs ago.

 

[teuchter]

If the question is how long it would take a motorway to disappear as in become undetectable in the landscape, I reckon you would be talking about thousands and thousands of years. Building any motorway (unless across really flat land) involves shifting a lot of ground (including solid rock depending on the terrain) to create cuttings and embankments, before you even start to consider the materials the road surface is made out of. I'd imagine that it could take more than a hundred years for all traces of tarmac to disappear depending on the climate. I've seen plenty of old roads in the Scottish Highlands, abandoned and unmaintained since the 60s when new ones were built to different alignments, which although overgrown still retain significant amounts of paved surface and that is in a wet climate and exposed to frost. A motorway will be constructed with a much thicker and heavier buildup than those roads, too.

Here is West Kennet Long Barrow which is more than 4,000 years old and still very much visible. Compare the scale of that to the kind of earthworks involved in creating most motorways.