Why does road design have to be the way it is?

I have always been curious why road design does not plan further into the future.  From what I remember from my college transportation design class, when a new design is first started, the design is based off of the projected population and expected volume 10 years into the future.  After the design process, the surveying, land purchasing, and obtaining permits have been completed the construction process begins.  Then, the construction process takes a a long time and by the time the road is completed, it has been 11 years since the original design and the road is over capacity.  I do not work in this field, but this question has baffled me since I took that transportation engineering class.  I am hoping some of the bright minds here at EB can enlighten me as to why the roads aren't designed so that they don't reach capacity until 5-10 years after they are built?  Do I even understand the process correctly or am I missing something?  

mainly federal funds and the NEPA process - what started out as a good thing to protect the environment when you build roads has turned into a ridiculous money grab and obstacle course to build roads (with federal money). too long to elaborate but there is a reason locals not using federal money can build the same roads in less than half the time than those with federal funding..

But why not take that into consideration when designing.  If they know the road will not be finished for 10 years, then why not design for the projected capacity of the location in 15 years?

they try to but in many cases by the time they get around to even then planning stages they are already 10-20 years behind - most of it is the Feds (FHWA, NEPA, etc). If they would just let states keep all their gas tax revenue and cut the Washington folks out of the loop it would be much better and up to date. Or at the very least trim them out - just make them basically a standards committee to ensure consistency, set which design standards are going to be used and then get out of the way.

Because projects 20 years ago were delayed due to the "process" it puts all the others behind at the starting gate, and since your normally dealing with hundreds of millions of dollars for interstate type  projects they go with the "give them what we can afford not what is really needed" approach.

Georgia raised the state gas tax 6 cents a gallon, no fed $$, they are in the beginning stages of cranking out major interstate projects in 2-3 years versus the normal 10+ years relying on federal funds. They are still having to do some ENV work since the interstates are "federal land" but its cut it back to the amount that it was probably intended to be in the beginning.

i.e. everyone who does road construction in GA is happy except the people that perform env "studies" and write environmental documents. & the travelling public will be happy soon as well..

So, a couple things.  Designing for 10 years into the future isn't really true.  Most projects I've worked on are looking at a design year 20 years into the future, and that is not from today's date, but from the anticipated construction year.  However, for big projects, I've seen a design year of 30 - 40 years out.  But, to be fair, it's all just an estimate anyway.  Who really knows how much traffic there will be in 10, 20, 30, or 40 years, and by that time we will almost certainly have significant advances in vehicles and the way we travel that will probably make our projections obsolete.

yeah that's why I say traffic is vudu, supposed to be LOS C for 20 years from open year - that always works out right?

Thanks guys. I am glad to hear there is an attempt to plan farther into the future than I originally thought.  Hopefully the process will safely speed up one day.