美国各个城市已成为推行创新性政策的试点，以减轻气候变化、逆转环境退化以及支持使用可替代性能源。美国联邦制度的特性使城市的创新性政策往往能被州政府及联邦政府采纳，将城市置于环保运动的核心地位。【请见相关文章：欧巴马总统认为气候变化对我们构成的威胁最大、北极冰层消融危及北极动物的生存、美国风力发电前景光明】

共用车道

几十年来，美国的道路设施主要为汽车服务。但越来越多的城市为了削减汽车的碳排放，鼓励居民用两轮的自行车来取代四轮的汽车。俄勒冈州（Oregon）波特兰市（Portland）引领着这一潮流，被人们冠以美国自行车之都的美称。

波特兰居民享有全美规模最大的自行车道路网络——全长超过500公里。该市还任命了一位“城市自行车协调员”，提供免费的自行车路线图，开辟了大量自行车停车处，当地一家快餐店甚至还开设了一个骑车购餐窗口。

波特兰的一些公司企业为骑车的员工提供更衣室，还通过现金奖励及其他奖励措施来鼓励员工骑车上班。今天，骑车上班的人占波特兰全部通勤人员的6%，在美国各大城市中占比最高。

为方便居民骑自行车出行，波特兰市开辟了多种自行车道：

• 自行车街道：供自行车和汽车通行的居民区街道。这些道路限定时速不得超过32公里。
• 自行车专用道：用水泥墩或路缘与机动车道隔离开来的自行车专用道。
• 共用车道：标有自行车图案以及两个指向前方的箭头的“共行箭头”道路标识标明自行车和汽车都可以使用这条车道。

波特兰提供的这些便利和奖励措施使该市骑自行车的人数自1990年以来增加了近五倍。

Cities as policy labs: Portland’s bicycle experiment

 This is fourth in a series on U.S. cities’ environmentalism, following Chicago, Pittsburgh andNew York.

American cities have become laboratories for novel policies to reduce climate change, reverse environmental degradation and support alternative energy. In the U.S. federal system, cities’ policies are often adopted at the state or national level. This puts cities at the center of the environmental movement.

Sharing lanes

For decades, America’s transportation infrastructure was built to service cars. But increasingly, to cut automobile carbon emissions, cities encourage commuters to use two wheels instead of four. Portland, Oregon, leads this movement and has become known as the unofficial bike capital of the U.S.

Portland residents enjoy one of the most extensive bikeway networks in the country — more than 500 kilometers — and count on a “city bicycle coordinator,” free bicycle-route maps, ample bicycle parking and even a bike-through window at a local fast-food restaurant.

Some Portland-based employers offer their workers locker rooms, cash rewards and other incentives to cycle to work. Today cyclists are 6 percent of all Portland commuters, the highest percentage in any large U.S. city.

To help people peddle to their destinations, Portland offers a variety of bike lanes:

• Bicycle boulevards. Residential streets  marked for both bikes and cars. They have a speed limit of 32 kph.
• Cycle tracks. Bike lanes physically separated from motor vehicle lanes by concrete barriers or curbs.
• Sharrows. “Sharing arrow”  street markings that show an outline of a bicycle and two arrows pointing forward, indicating that both bicycles and cars can use the lane.

These conveniences and incentives have produced an almost fivefold increase in the number of bicyclists on Portland’s streets since 1990.