projections of traffic jams doubling by 2010. Also, the elevated structure itself was decaying, after more than a half century of continuous use. For most of the 1990s and early 2000s, driving in Boston was disrupted by the Big Dig, the most expensive (roughly $14 billion) road project in the history of the US. After more than 15 years of disruption, The Big Dig, along with other highway projects, provided less than 10 years of relief before congestion returned to the levels seen in "prerecession 2005, when the Big Dig was almost complete and marketed as the solution to gridlock for commuters ... analyses would conclude that the added capacity attracted more drivers, and pushed the traffic bottlenecks farther into the suburbs." However even without the big dig the raised road was structurally deficient and needed rebuilding or replacement. Boston remains one of the most congested metropolitan areas in the US. The complex and still-changing road network, with many one-way streets and time-based traffic restrictions, has led many Boston travelers to consider an up-to-date GPS navigation map system a necessity. Walking and bicycling Boston is known to travel agents as "America's Walking City", has been rated as the third most walkable city in the US by Walk Score, and also has a high Transit Score. Boston is a compact city, sized right for walking or bicycling. According to a Prevention magazine report in 2003, the city has the highest percentage of on-foot commuters of any city in the United States. In 2000, 13.36% of Boston commuters walked to work according to the US Census. This was the highest of any major US city, bested only by college towns such as nearby Cambridge. Most of the area's cities and towns have standing committees devoted to improvements to the bicycle and pedestrian environment. The first pedestrian advocacy organization in the United States, WalkBoston, was started in Boston in 1990, and helped start the national pedestrian advocacy organization America Walks. Cycling is popular in Boston, for both recreation and commuting. Some bicycle paths are marked on some roadways, but very few completely separated paths are available to cyclists. The Minuteman Bikeway (which runs through several suburbs northwest of Boston) and the Charles River bike paths are popular with recreational cyclists and tourists. The Emerald Necklace system of parklands and parkways, pioneered by Frederick Law Olmsted and his sons, provides some more pleasant alternative