Driving In America
Posted by Dave Cohen on May 17, 2006 - 12:08am
I am driving I70 from Boulder on my way to Pittsburgh in my 1988 blue VW Jetta.
Dave's Car (not really, but close!)
So with oil a shade under $70/barrel and gasoline at about $2.80/gallon on the interstate in the Midwest, I thought I'd report on what's going on out here. I hope you'll add your comments to this brief road trip report. I'm sure many of you have plenty of experiences to report.
However, if I drive any slower, I become a road hazard. One thing to note (I've long seen this) is that people drive really fast in packs (like wolves). You'll be driving alone for a while, not a car in sight when out of the blue, one of these vehicle wolfpacks is right on top of you moving about 85/mph and there's the biggest long haul truck that you've ever seen tailgating you. And he's really pissed that he had to slow down to 65 and couldn't pass you because the rest of the pack is taking up space in the passing (lefthand) lane. I can honestly say that the only people I've passed (going 65) are slow movers pulling out of rest areas.
Remember when Jimmy Carter told us all to slow down to 55/mph? In any case, no one I've seen cares at all about what is also referred to as fuel economy.
The exurban and suburban sprawl began about 30 miles outside of Kansas City in both directions (west of it in Kansas and east of it in Missouri). I took note of the Walmart Supercenter at about the 30 mile mark in Missouri.
It seemed to be out in
the middle of nowhere
I'll add one last thing. Some miles outside of Kansas City at about 3:30 PM CDT I ran into the first of several traffic jams on the interstate as I tried to negotiate my way through the city to the other side. The highway was in total disrepair just as I've seen in other heavily traveled areas. In my old hometown, Boulder, road maintenance used to be seasonal. Now, it's constant--all year round on the major roads. Not all the traffic jams were due to repair. There was just one hell of lot of cars & trucks out there. The wear and tear on the national highway system (started during the Eisenhower administration) is appalling. Well, it's been a horrow show so far and I don't expect it to get any better.
Columbia, Missouri with 2 days to go. Signing off.
-----------------------------------------
Just outside Indianapolis, 1 day to go.
The big news I heard today was from an AM radio station in which I heard that Texas is considering raising the speed limit to 80/mph.
But a study by the Texas Department of Transportation (TxDOT) found that 85% of drivers on the affected highways already drive 76-79 mph, says Carlos Lopez, the agency's traffic operations chief.Which means that people in the affected areas will actually drive 86 to 90/mph. Various callers to the talk show praised the idea.TxDOT has been studying the proposal since the Legislature last year authorized increasing the speed limit from 70 or 75 to 80 mph in 10 mostly rural counties.
The closer I got to Indianapolis, the faster and more aggressive the drivers were, especially the trucks. I was tired and didn't feel like dealing with nonsense, so I pulled off early to preserve my own life and those of others. Road conditions did improve after Missouri, so some of the comments on this thread are certainly correct about the roads there.
Rough calcuations show that I'm getting at least 35/mph. Not bad for an 18 year old car. Later.
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of course i won't give my exact address, you understand right? :P
Half kidding, half not kidding.
Appropriate to the site..
so is your tank half full, or half empty?
Haa...depends on whether I just got paid or not.
I was just wondering if the KC area folk would ever want to get together in a central location sometime. No rush, no hurry, no pressure. Those that don't want to reveal themselves (ahemmmm...TrueKaiser) can remain anonymous, but it might be cool to shoot the bull.
If anyone's interested I'll give out an email address. If not, that's fine too.
Ironically (to Dave's journey), I'm driving out to Denver tomorrow for a wedding tomorrow in my wife's Prius. I'll check back on this link to see if there are any takers to the local gathering.
My car (2002 Camaro V6) has a sweet spot in 5th gear at about 2400 rpm. On the highway that equates to about 70-80 mph, depending on the terrain. At lower speed in 5th gear, I don't have enough torque to pass safely and I have to row alot between 4th and 5th. Any higher and I'm inviting a ticket.
My car is EPA rated at 19 city/24 highway and I average about 21 in the city and 32 on the highway.
The problem with that is that most people end up constantly speeding up and slowing down, in which case you end up lugging the engine pretty badly at such a low speed. So people tend to get better mileage at a slightly higher speed. Also, some automatic transmissions work differently at different speeds, so the torque converter may not lock until you reach a certain speed. The locking of the clutch improves fuel economy at that point and above (see torque converter at howstuffworks.) Automatic and manual transmissions are different in terms of most economical speed.
Our wagon with a manual transmission gets its best fuel economy at about 30mph, but you have to pay constant attention to the amount of gas you're giving it and the terrain/conditions ahead.
More disconcerting is sometimes it makes a jump such that it jerks to that "afterburner effect", creating a mild "catapault effect". This occurs at a slow speed then jerks and accellerates good. Good thing I have 5 years left on the warranty. Both of these effects are probably growing pains as Kia was a new make in Year 2001 when the car was made.
I know that an auto trans is never as fuel-efficient than a Stick but I can't drive a Stick. As far as the auto trans, the two hunting related effects occured immediately after a trip to a Jiffy Lube when they filled it, but it existed beforehand. It's probably a design bug.
But what do people here think of the "Joe Cell"?
Basically, it's a device that, using only water in a stainless steel tube with concentric rings... can produce enough "energy" to power a car... without depleting the water.
Here are some links... I'm very sceptical.. but given the implications, and our current Peak everything scenario... well, everything is worth a look right?
http://peswiki.com/index.php/Directory:Joe_Cells
To quote the above site:
I always thought that big trucks were not allowed in the leftmost lane of multilane highways. Does anyone if this is true and what the law is on this?
I've experimented with going 55 mph on interstate highways, and it's quite luxurious. I view it as guzzling time instead of gas. Since you will pretty much never be overtaking anyone, you can use your cruise control in heavier traffic than you normally would.
Perhaps that's true but maybe somebody else could check it out. One thing I know is this--they are driving 80/mph in whatever lane they're in most of the time. Of course, they do not need to accelerate to pass me, all they have to do is turn the wheel to the left and when they're done, back to the right.
Cal has a 55 mph limit on trucks, meaning they only go 70. Thru the SW, they were going 80. The ones doing 78 were passed by the other truckers doing 80. Took like 5 miles for them to pass.
I was trying to keep my speed close to the limit, having California plates in Texas, and all. I'm doing like 75, and look in the rear view. Here comes a big screaming truck, an open shark's mouth for his grill. Hey, I'm not gonna let him eat me :>)
They should take those trucks off the highway and put the trailers on the trains we saw.
Rat
or "Trucks over 6 wheels must use two right lanes".
You're asking for a very expensive ticket.
The thing that frustrates me is that I have an Amtrak station in Lee's Summit that goes directly to Kansas City, but there is no commuter line set up. I long for the old days when trolleys were everywhere.
Hope you enjoy Columbia. There is a fantastic winery at Rocheport near Columbia with a restaraunt overlooking the Missouri River. The Katy Trail bike path also winds along the river just under the restaraunt.
Yea, I live 'nigh the center (only 10-15 minutes from downtown) and I love to mock those who live out south for "living in the middle of nowhere", even though that area is ridiculously developed. True also that most traffic jams are caused by road repairs- which can be constant (I've had several 20 minute drives turn into 2 hour nightmares).
What I'm curious about though is if you noticed the Missouri/Kansas split. Kansas spends more on its roads and has less roads to maintain, so they tend to be in pretty good shape, whereas Missouri has the largest (correct me if I'm wrong) amount of pavement per capita in the nation and yet has to maintain it with one of the lowest gas taxes. Besides the subtle potholes, this difference is most accute in the winter, when you drive down State Line and the Kansas side roads are perfectly plowed and salted while the Missouri ones remain coated in snow.
Oh. The other Kansas Missouri split might be more subtle. Kansas City, Kansas has embraced suburbia as its development plan, concentrating most resources on the "speedway", which is a huge box store retail/everything else/huge huge parking lots development centered around a speedway while entirely neglecting its half of downtown. Kansas City, Missouri, on the other hand, is bent to what has become the biggest downtown renewal project in atleast 50 years, with a new arena, urban retail center, performing arts center, and a plethora of other stuff tending toward urban rather than suburban development.
Anyway, couldn't let you go through KC without giving you a bit of an update.
thanks for your remarks, Dave
Also Jonathan Franzen's thriller cum satire 'The 17th City' is also set there, I believe. A strange novel but a very clever one.
Thomas Frank 'what is the matter with Kansas?' is quite evocative of KC, where he grew up.
Drive a battery electric vehicle. You might like it.
Drive a plug in hybrid vehicle.
Drive a hybrid electric vehicle.
Drive gently; don't spill the martini.
Drive slower than 60 MPH.
Install a front air dam.
Use a mirror alternative.
Smooth the underbody.
Slam (lower) the car.
Use an efficient ECU (like the Honda HX).
Add wheel fairings.
Install low rolling resistance tires.
Ban automatic transmissions.
Manual brakes.
Manual steering.
No air conditioning (use in-seat fans?).
Windows down when parked, up when driving.
Get a smaller car.
Get a lighter car.
Go smaller displacement (1.0L should be enough).
Aluminum block, cylinder head.
Remove heavy junk (shotguns in the back?)
Inflate the tires properly and instrument tire pressure.
Change the air filter, plugs, EGR, etc.
Instrument instantaneous mileage (based on MPH and injector).
Install wheel fairings.
Streamline like the Dymaxion.
Speed govern at 65 MPH.
Install HID headlights (and LED tail lights).
Drive only on hot days (global warming should help).
Run stop signs.
Draft the trucks.
Drive superconducting maglev in a vacuum.
Tongue in cheek....
The ultimate way to save gas is to have a magnetic hitch that allows you to hitch to the semi when you turn on the magnet. When he diverts from your course, you detach and look for another truck to bum power from.
About that maglev in vacuum- get ready to duck. Last time I advocated it, got smothered in heavy barrage of odious adjectives. But hey, aren't these things in every sci-fi story? Gotta be good, yes?
Drafting trucks is good duty, Did it all the time in the old VW bus days-big jump in terminal velocity. Long rope with iron-neodymium mag even better. Check brakes & reflexes first.
Seaman first class wimbi
I hope you have fun Dave, moving is both a joy and a pain, but its something we should all do to get the junk off the shelf and given to someone else.
There is a BIG house farm on I-385 in Memphis wow, they keep putting in more and more homes. The places around here just keep spreading too. I wonder what Sterling will be like, Terra-server veiws of it, make it look small.
I will be able to walk most everywhere I need to go I hope.
At one point we passed a station wagon that had a rear wheel beginning to go flat and we could smell the rubber. Fortunately we managed to pull alongside and hand-signal to the woman driving (and family in back seat) that she had a flat and they pulled off. Would've been nasty with a blowout at that speed.
Probably because vehicles with a potential weight above 3500kg are not allowed to go faster than 80 kph (50mph), and are physically incapable of going faster than 90 kph due to a mandatory speedlimiter. Needless to say, most truckdrivers dont care for the 80kph limit, but they have no choice but to obey the device in their truck that physically limits their speed. The funny thing is, that 80kph speedlimit applies to the american style SUVs and pick-ups aswell, but AFAIK they are not equipped with speedlimiters, and their owners dont seem to care more for speedlimits than people driving normal cars.
I used to occasionally drive a 16 seat minibus on one of the very few stretches of road in Norway with a speedlimit as high as 100kph, and just for fun I once tried to stick to the 80kph limit the law required. It was not much fun it turned out, all kinds of vehicles from motorcycles to 50-ton trucks were passing me constantly, and I was probably cursed by many a truckdriver struggling to get into the left lane and overtake me, but I kept the experiment up for the road went back to single lane. The moral must be to stick to the de facto 90kph limit if you drive a heavy vehicle. Ofcourse, the vast majority of roads in Norway are 80kph, so most of the time I drive 80 regardless of what vehicle I am driving. Most people drive 10-20kph above the speedlimit, and traffic is getting more aggressive by the year, but I dont feel bad when a long line is building up behind me when I keep at or slightly above the limit.
I have a benchmark trip of 528km that I drive a few times a year in a 1989 Opel Omega 2.4i 125HP station wagon, and I monitor the fuel consumption with great interest. The engine displacement is huge by norwegian standards, so I was surprised when I found I could drive it very economically if I wanted. Some examples of comsumption:
33L--6.25L/100km--38MPG, alone in the car,dry roads, summer tires, very careful manipulation of the gas pedal
45L--8.52L/100km--27.9MPG, 4 passengers, trunk full of baggage, winter tires, roads covered in snow/ice.
40L--7.6L/100km--31.35MPG, typical drive, 2 passengers, some baggage, occasionally speeding slightly.
Now I must get out and celebrate the constitution day :)
When they reach a border control post or gendarmerie post, they can be stopped and checked for any speed infractions. Fines levied on the spot.
As a result, European truckers do not speed.
In Italy, like in France, the autostrada are toll roads. The locals use the non toll roads. So the highways are not busy but the local roads are jammed.
The net effect is actually more accidents, because limited access high speed highways are actually the safest roads there are (caveat: if you do crash, you will die). This is a generic problem with highway tolling.
It is cars entering and leaving the road which causes the majority of accidents.
Agree with you the average human response time is too slow to make 85-90mph safe. However there was nearly a civil revolution when Germany proposed to put any speed limit on an Autobahn. There is a reason the Mercedes and BMW perform so well at high speed! My cousins were doing 70 mph, and were rearended in the middle of the night driving back from Berlin to the UK.
Zurich has a 'Car Drivers Party' which managed to get a quite substantial share of the vote, when the government proposed driving restrictions in the city core.
I think a lot of people also have no choice inasmuch as they have committed themselves to these HUGE commutes every day: if they went any slower, they would get zero time with their kids/family, etc.
Fundamentally there is also a deep distaste (at least in me) for sitting behind the wheel. Anything I can do to minimize it is a Good Thing.
That said, last weekend I drove 160 miles round trip, Orange County to San Diego, and had similar experiences: everybody else going 75 to 80, and I had the cruise locked in at 63mph in the right lane, just because I wanted to sightsee, I wasn't in a hurry, I drive a crappy old pickup truck, I was just going to a birthday party, I was chillin' and enjoying the ride because I rarely do it (once a year or so).
I'm slowly building up yearly trips though, a yearly one to Sonoma, one to Sacramento, etc. But those are more like breaks or mini-vacations though.
If and when we do get that, longer commutes will be much more tolerable, because you can relax and read, watch TV or talk while your car takes you to work. The car can then go and part somewhere distant, and you can phone it to come by your office when you are ready to leave.
He also pointed out that even in crowded conditions, cars take up only about 10% of the road. 90% is empty space between cars. Computer-controlled cars will be far more precise and can communicate with each other, allowing for much denser packing. The result will be that our existing roadways will be able to accommodate many times the traffic they can carry today, reducing congestion and making trips much faster.
But I oppose the proliferation of UNMANNED guided cars. This would waste fuel, clog streets, and make a road-going cruise missile too easy for terrorists. A terrorist cell could get a bunch of ANFO supplies, rent out a fleet of guided cars, and launch a salvo of cruise missiles roaming the streets hitting targets. Laws would have to be made to forbid unmanned cars and make for stiff penalties for the abuse of guided cars.
Back in the 1990s I got into a USENET discussion about just this topic of guided cars. (my word for "computer controlled cars")
Yes, we are making enemies faster than could have been imagined, and perhaps someone will do some damage. But compared with the damage that will be done by climate change, economic collapse, and the social unrest I expect will be all around us before too long, it's not worth my worrying about.
If you look at SW Asia, the Horn of Africa and other noted trouble spots, they are also suffering from drought, soil exhaustion, population pressures, etc. Islamicisation is sweeping the former Soviet Central Asian republics, where the conditions are some of the most desparate in the world (draining of the Aral Sea due to water supply pressures etc.).
Many of the future wars will be about water and oil: arguably the First Gulf War was the first oil war.
Perhaps we should declare an unending war on colon cancer, and throw trillions of dollars at it instead?
Four possible routes.
The longest, 69 km, is in most traffic conditions, the quickest (it involves taking the ring road 270 degrees around my destination city of Lyon).
The shortest takes me through a long toll tunnel(1.80 euros, about the price of 1.5 litres of fuel, or 20 km worth), but the traffic jams at either end of the tunnel in peak periods.
The other two take me straight through the middle of town, and are shortest, about 55km, and take no longer than the others if it's after about 7pm...
Time is absolutely critical, an hour's commute is all I will tolerate. Luckily I have flexible hours, so I can generally stay fairly close to this. When I have to arrive before 9am, it takes an hour and a half at least.
Where it starts to get complicated is... I sort of have a public transport option. I can drive about half the distance, then take the train. The cost is competitive, but the problem is that the station is a couple of miles from the office. In practice, the various public transport options for this last leg just push it over my threshold for time and hassle. This may change of course...
The obvious lifestyle trade-off, given that I am both unwilling and unable to move to town, is to find a girlfriend in town...
Or, perhaps less trouble: any compatible person willing to supply living space in town during the week, in exchange for living space in the country during the weekend. Sort of house-pooling.
I also marvel at how many people tell me that their mileage is better at 65-75 than at 55, without ever having tested it! I know that I get the best mileage at 55 but I typically drive in the low 60's so as to be in less danger of being flattened. I wouldn't be surprised if I could do even better by driving 45-50 (right at the edge of lugging the engine).
Also, a question to somebody with engineering experience - how much of a difference does the drag coefficient of a car make for its efficiency "sweet spot"? I know that air resistance basically increases at the square of velocity, but I wonder whether making a more aerodynamic vehicle would affect the speed of greatest efficiency or whether it would simply reduce the total amount of energy required to maintain that speed. Thanks.
you would need to be doing about 3-400mph for the coefficient of drag of these cars to have any meaningful effect, probably better to buy some racing slicks to lower the drag! :)
The answer is not all that clear cut. You've got to keep in mind that a car's fuel consumption is the sum of several different components, the main ones being: i) thermal efficiency of the engine itself, ii) engine and drive train friction, iii) rolling friction, and iv) aerodynamic drag.
Thermal efficiency is determined by the engine design and to a lesser extent the operating speed of the engine (usually best at not too low and not too high of an engine RPM).
Engine and drive train friction is pretty constant with regard to the car's speed, so this fuel consumption component will not change much with speed.
As you correctly pointed out, aerodynamic drag increases with the square of the vehicles speed. Generally, this component starts to get more and more significant once you get up to around 50 mph or so. It is also often the main factor that limits the top speed of a vehicle.
Having said all that, I seriously doubt that within the speed range of most highway driving, i.e., 55 to 75 mph, that there is any 'sweet spot' for fuel consumption. The engine is already well within its most efficient operating range. So, if I had to bet money, I would bet that if you took 100 cars and measured their fuel consumption at a steady 55 mph vs that at 75 mph, you would find some variation, but in general you would find consistently worse fuel consumption as the speed increases.
Depends on the engine. In an Otto-cycle engine, the throttling losses will decrease with increasing engine load, so the engine efficiency will go up as the speed goes up. For a diesel engine, it's the opposite; your engine friction rises with speed so efficiency goes down.
My Passat registers 60-70 MPG on the trip computer when ticking along at 40 MPH in fifth. This figure drops with speed to about 44 MPG indicated (~40 true) at 65.
One of the most important things to getting good mileage is to pay attention to what is up ahead and conserve momentum. Avoid any unnecessary throttle openings by slowing down a little sooner and leaving a gap to the car in front as you come up to a stop - try to avoid the extra starts and stops. Every time you move the throttle plates open the fuel system enriches the mixture for acceleration.
So those fully loaded 18 wheelers that are now the norm in transport, pioneered for logistics by Big Box retailers like WalMart, are doing something like 8 times as much damage to the road surface as an ordinary car (for twice the axle loading).
And heavy SUVs will not be helping.
The radical decentralisation of the US into 'Edge Cities' in the last 20 or 25 years has made the problems of road congestion and road wear and tear much greater. The US has reached the end of the 'suburban' development model, and moved to the 'exurban' one.
An irony of moving out is that people drive more, and it leads to more congestion, not less.
A classic sign of this. All the growth in retail space in the last 20 years has been in Big Box, standalone formats (WalMart, Home Depot etc.). I believe there has not been a major new shopping mall opened in the US since the early 90s, and all of the existing ones are either struggling, or transforming themselves eg by having more boutique shops, restaurants and entertainment.
With a decent, and steady, tailwind, I got 40 mpg in my 2001 Toyota Corolla (automatic, EPA rating of, I believe 36 mpg highway) driving about 73-74 mph coming back to Dallas from Big Bend National Park.
I was on Interstate 20 and I naturally had the cruise control locked in. The tailwind was about 15 mph or so.
That said, with the cruise on, at that same speed and no tailwind, I will average about 38 mpg. The one engine "maintenance" item I do is to pour some Coleman lantern/stove fuel in the tank about every dozen fillups or so. (White gas is naphtha, one of the primary petroleum distillates in gas treatment mixes, and a heck of a lot cheaper>
I make no apology for driving faster than 70. West Texas, let alone the mountain/intermountain states, are large and sparsely populated.
Next thing you know we'll have TOD Pittsburgh!
talk to you soon, Dave
Thanks for bringing us along!
When my wife and I moved from NYC to Maine, we took 3mos off and drove the country to get to a lot of National Parks hiking,etc. Realised the Subaru did a lot more 'hiking' than we did, but it was a great trip.
One of my favorite (self-righteous indignation) sights was the Tourbus-sized RV's, towing not a Mini Car for local running around, but a full-SUV behind them, and on which we often saw ATV's on the roof racks, Motocross on the tail racks, Motorboats, etc. I am really sorry now that I never got a decent picture of this egregious mess. If you see one and can do it (safely).. want to post a snap or two of this uniquely american 'doesn't-much-' caravan?
Bob Fiske
http://www.forbes.com/home/feeds/ap/2006/05/17/ap2753259.html
Just little musings to keep me entertained on the drive!
Also the Romans used inland waterways a lot, an area which has been neglected (for lack of good archaelogical evidence).
There is a Joe Haldeman short story, 'Armaja Das', about a gypsy curse which leads to WWIII (this is less goofy than it sounds-- the computer systems are built with sensitivity circuits, so they pick up the curse, however the defence computers are not, so they notice that the country is apparently under attack, and respond). It's really a (pre internet) description of a massive computer virus attack.
In the end of the story, the gypsy mother is riding her horse and cart along a ruined highway. It is a very evocative image.
http://www.fantasticfiction.co.uk/h/joe-w-haldeman/infinite-dreams.htm
Given the overpasses (which will collapse rapidly) the roads would probably be far less usable than we might, at first, think.
The slabs of the Roman Roads made good building materials, I am not sure what makes up an Interstate is recyclable for the same purpose.
Part of the plan was to allow rapid evacuation in case of an atomic emergency, and also to allow movement around the country even if key cities had been destroyed by atomic bombs.
Once the hydrogen bomb was developed in the mid 1950s, (far sooner by the Russians than had been anticipated), the devastation of each bomb would have been much greater, and the idea was somewhat obsolete.
An unintended side effect was that people moved out of city centres and commuted to work greater distances. The modern Edge City would have been impossible without the expansion of the Interstate network. Also the urban planning of the time was that it was OK to bulldoze established communities, which were merely 'poor' to build roads right through the centre of town. The Boston Big Dig has been about reversing that.
In Manhattan, Jane Jacobs and a few much derided 'hippy mothers with strollers from Greenwich Village' managed to stop Robert Moses from building an on ramp through half the village-- the first time anyone had ever defeated him.
She then moved to Toronto and stopped the Spadina Expressway being bulldozed through what is now one of Toronto's nicest neighbourhoods (the Annex).
If we really are reaching Peak Oil, then North America will owe her a significant debt. Many of the urban neighbourhoods have survived because her ideas inspired a generation of urban activists.
Interestingly, in her last book, Dark Age Ahead, she became increasingly pessimistic about the prospects for North America, focusing on what she termed the decline of 'responsible' civic behaviour.
www.amazon.com/gp/product/1400076706/sr=8-5/qid=1147976075/ref=pd_bbs_5/102-5165299-0862522?%5Fencod ing=UTF8
On the subject of cities, she was undoubtedly a visionary, and a woman before her time, although she would have derided the 'gentrification' and upper middle class professional ghettoes that places like Greenwich Village have become.
Along with JK Galbraith and Betty Friedan, I think we will come to miss their wit and insight very much.
Also, a lot of bridges & overpasses use steel wideflange beams, or steel trusses, that will eventually rust out.
However, I would not expect asphalt-based roadways to last long into the future.
Being petroleum based, much like synthetic tire rubber, they are very vulnerable to UV destabilization and degradation (ever noticed how old asphalt roads are much lighter in color than fresh asphalt?), cracking, crazing, and subsidence crumbling (aka potholing).
On the whole, they will fairly quickly come to resemble arrow-straight sections of the surface of the moon.
You can see this on any asphalt road that has not been repaved in 20-30 years or so, much less with heavy useage.
Concrete-based roadways will hold up much better, overall. The biggest problem with them is the freeze-thaw cycle and salt degredation (in those states where deicer is used).
I am thinking of that suburb of Detroit where they built the infrastructure (in the 1920s?) but never actually built the community.
The cold air underneath an overpass aids the freeze-thaw cycle, and they decay.
Also the metal in rebar corrodes.
Many of the overpasses are just going over another highway anyway - at much slower speeds they are not required. They would just be intersections, which is where the taverns get built! Real bridges over rivers are usually better built.
River crossings are the key-- there you would find barges and bridges with tolls, baronial castles and taverns. The map of the fur traders' routes in the early 18th century, and the pioneer trails, is probably a better guide than the modern road network, in many places-- getting over the Appalachians, crossing the Mississippi etc.
Cities like St. Louis are strategically located re river transport and the passability of the tributaries of the Mississippe delta, and I imagine that would return. Ditto places like Boston and Manhattan were key for their sheltered harbours and their water traffic, and again that would be important.
There is a Michael Kurland novel 'Pluribus' about the US after a plague has killed 90% of the population. The description of travelling across the US is very evocative. Civilisation is clinging to the margins but, inevitably, a movement has emerged that it is civilisation which caused the plague (invoking God's wrath) and that movement seeks to end the use of technology.
http://www.fantasticfiction.co.uk/k/michael-kurland/pluribus.htm
If you want a plausible scenario for the breakdown of American civilisation into civil disorder, then Joe Haldeman's 'Worlds' Trilogy
http://www.fantasticfiction.co.uk/h/joe-w-haldeman/worlds.htm
is quite good (particularly the first two).
Agree the routes will last forever. Just as modern English roads are often Roman ones (you can tell-- the Roman roads are as close to straight lines as possible).
However if you read about the conditions of roads in England in the Dark Ages, or indeed in the 17th century, you can see how far backward things can go. I am reminded that the early Anglo-Saxons shunned the ruin of Roman London-- they thought the buildings must have been built by giants.
There was also a movie with Lee Majors and Burgess Meredith, about the last race car driver trying to escape a government which mandates solar powered cars
http://www.imdb.com/title/tt0082642/
Burgess Meredith is the last fighter pilot, assigned to hunt him down as he drives across a ruined United States. The movie is B grade (B minus minus) but again the imagery is quite evocative.
So anyway, this was a fun thought experimant/fantasy, but I don't think that our near future looks this way. Even if major "collapse" (whatever that actually means) happens, there will still be cars on those highways for quite some time. There may be ever fewer, with the highways increasingly negelcted, but nonetheless they will still be used. Maybe in 200 to 300 years though.....
Either the next 50, when we figure out how to reconcile the rise in CO2 emissions and our appetite for travel with the global climate change, and how we move to non carbon fuels
or we won't deal with it, and in 100 years the highways will be empty, with trees sprouting through them.
In 200-300 years our civilisation will either have moved on to a more sustainable track, using solar energy or its successors (eg nuclear fusion, solar power satellites) or we will be but a memory.
If our civilisation is still around in 200-300 years, then
- people will complain about the traffic
unless
- we are into flying cars or matter transmssion, in which case people will complain about the traffic and crowding in the airlanes, or at the matter transmission booths!