State officials and bicycle enthusiasts are stitching together more than 50,000 miles of pedal-friendly pavement to form a vast network of bicycle routes connecting byways, cities and offroad trails in a system like the one created for cars and trucks over half a century ago. The American Association of State Highway and Transportation Officials, working with the Adventure Cycling Association and other groups, recently approved a plan, four years in the making, that lays the foundation for the network. Now it's up to each state to create the routes and put up signs. It's a big turning point," said Jim Sayer, executive director of the Adventure Cycling group, the authority on transcontinental bike travel. The effort relies on cartography instead of construction, signposts instead of earth-movers. Working from a bewildering tangle of existing roads, planners mapped a web of corridors where the national bicycle system should go. They considered traffic volume, terrain, amenities and ways to link together lightly traveled byways, secondary roads, urban trails and already established transcontinental bicycle routes.