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The first step in building a road is to plan the route. Sometimes the route has been decided by the nature of the land ① ， but today nature can often be conquered. With powerful modern machinery，whole mountains can be moved and valleys be filled in to make the route as direct as possible.
Then the details are planned： the width of the highway， the number of driving lanes， the number and location of entrances and exits， and the essential strength of the road. All these depend on the amount of traffic that is expected. Modern roads are usually planned for the next 20 years’traffic.
The next step is the testing of the earth foundation on which the road is to rest. Engineers carefully study the soil to learn how solid it is， how much moisture it contains， and how well it drains. Then they decide how the soil should be prepared and packed to provide a good， sturdy foundation， or roadbed. They prescribe the thickness of the road layers， the size of the rocks in them， and the other materials that should be used.
While the testing is under way， a group of surveyors begin to measure the land to find out exactly how much work needs to be done and how much it will cost. Then the construction crew can finally move in.
Giant bulldozers clear the path for the roadbed. They knock over trees and tear large rocks out of the ground. Other powerful earth-moving machines， such as loaders and scrapers， follow in their tracks， scoop up earth and rocks， and dump them into low spots. These filling materials are pressed down tightly with power rollers， and gradually the roadbed becomes a long， level band of hardpacked dirt.
Proper drainage is essential in road building， because if the foundation became soggy， the heavy road would sink into it. And if the water were to freeze in the ground， it would expand and crack the road. To protect the highway from such damage， drainpipes called culverts are laid across the roadbed wherever a strong flow of water is expected. The roadbed itself is shaped so that the middle of the finished road will be higher than the sides. Then water and melting snow will easily drain off its surface into the drainpipes or ditches ② . The roadbed is given a final grading（smoothing） and is now ready to receive the road itself.
Almost all roads are built in two or more layers， or courses， of rocks or stones. The bottom layer is 10 to 20 centimeters thick and usually made up of larger stones. The upper course has smaller stones and is about 8 centimeters thick. In most roads the lower course is wider so that the edges， or shoulders， of the top course do not break off or sink into soft dirt. After each course is laid， it is compacted by heavy power rollers.
The top， or surface， layer of a road must withstand the weight of heavy vehicles. It must also prevent water from seeping into the roadbed and destroying it. Modern highways are therefore surfaced either with concrete or with bituminous materials， such as asphalt， tar， or heavy oils.
conquer v. 征服
machinery n. 机械，机器
lane n. 车道
driving lane 行车道
inside / outside lane 内/外车道
entrance n. 入口
exit n. 出口
moisture n. 湿度，潮湿
drain v. 排水
drainpipe 排水沟管
drainage system 排水系统
pack v. 压紧；夯实；包装
packing course 填层
packing density 夯实密度
prescribe v. 规定，指定；开（药方）
surveyor n. 勘测者，测量员
crew n. 全体队员
construction crew 施工队
bulldozer n. 推土机
loader n. 搬运机，运土机
scraper n. 铲土机
scoop v. 铲起，舀出
dump v. 倾倒
roller n. 压路机
power roller 电动压路机
soggy a. 湿润的，湿透的
crack v. 使破裂
culvert n. 涵洞
ditch n. 沟渠
grading n. 土工修整
edge n. 边缘
shoulder n. 路肩
withstand v. 抗拒，经得起
seep v. 漏，渗
concrete n. 混凝土
bituminous a. （含）沥青的
asphalt n. 地沥青，柏油
tar n. 沥青，柏油
be under way 正在进行
knock over 推倒，弄倒
in one’s tracks 随即，立刻
filling materials 填料
sink into 陷入
①nature不带冠词时意为“大自然”，例如：Nature is at its best in spring.大自然在春天最美。但the nature指“天性”“本性”“性质”等，因此文中的句子：Sometimes the routes has been decided by the nature of the land…应理解为“有时路线由土地的性质确定”。
②drain（ v. ）into…意为“（水之类的液体）排放到……中”，本句可译为“然后水和融雪会顺畅地从路面排入排水管或沟渠”。