When engineers began monitoring traffic on a dual carriageway outside london , and compared it with traffic on roads inside the city of london , they discovered regular use of jammers , with 10 incidents per day by some roads .
A trickle of trucks flows along its single-lane carriageway , which stretches for less than 1km ( barely half a mile ) .
在这条全长不到1公里（约半英里）的单车道上，仅稀稀拉拉地行驶着几辆卡车。
On a two-lane carriageway , drive in the left-hand lane except when overtaking .
在双行车道上，除超车外，须靠左行驶。
But on the outskirts of the city , just off a busy dual carriageway , is the collection of low-rise , landscape-gardened buildings that make up the cambridge science park .
在城市的外围，繁忙的双向车道边，有一片由低层、园林风格的建筑物组成的地方，便是剑桥科技园了。
Minimum horizontal clearances of 500mm should be kept between the carriageway and obstructions on the footways , verge or central reserve .
