The dimension of a straight road is simple. Figuring out the space needed in corners can be very difficult. For the Dinamo-MCC course I have created some slides to explain the problem and to give some sollutions. The ideas are based on the works of Sebastiaan Depke.
A exctract can be downloaded here: http://www.1op87.nl/images/stories/roads/MCCworkshop2_pages_6-17.pdf
A alternative analyses is found on the website of DC-Car: http://wiki-en.dc-car.de/index.php?title=Kategorie:Road_construction
