Monday, May 6, 2013

Civil Engineering: Traffic Problems in History

All roads lead to Rome . . .

 The Romans built a huge network of roads. They were primarily for military use, but also used for trade. In all, the Romans built over 50,000 miles of hard-surfaced roadway.

Before the roads were paved, the weather could slow down any kind of travel. Rain could wash away sections of road, flood areas, or turn highways into mud bogs after many feet trampled the soggy path.

In those days, you had to walk most places – imagine getting your best pair of Corinthian leather Birkenstocks stuck in a mud hole halfway from home!

"Where we're going, we don't need roads . . ."

In Italy, the engineers developed a form of concrete, made from volcanic ash and lime. They used this to build roads that were strong, straight, and cambered, to allow the rain to run off.

In Pompeii, the roads had other “modern” designs built in. They had crosswalks that were raised, so pedestrians could stay out of the mud. They also used white stones as reflectors, placed at regular intervals down the center of the road. These were bright enough to catch the light from the carriages.

That's a raised crosswalk, so pedestrians didn't have to walk in the dirty streets.
The wagon and chariot wheels were standard widths, so they could pass between the gaps in the stone.

A cross section of Roman street design, from:  A Dictionary of Greek and Roman Antiquities. London: J. Murray.

The general appearance of such a metalled road and footway is shown in an existing street of Pompeii.
(A). Native earth, levelled and, if necessary, rammed tight.
(B). Statumen: stones of a size to fill the hand.
(C). Audits: rubble or concrete of broken stones and lime.
(D). Nucleus: kernel or bedding of fine cement made of pounded potshards and lime.
(E). Dorsum or agger viae: the elliptical surface or crown of the road (media stratae eminentia) made of polygonal blocks of silex (basaltic lava) or rectangular blocks of saxum qitadratum (travertine, peperino, or other stone of the country). The upper surface was designed to cast off rain or water like the shell of a tortoise. The lower surfaces of the separate stones, here shown as flat, were sometimes cut to a point or edge in order to grasp the nucleus, or next layer, more firmly.
(F). Crepido, margo or semita: raised footway, or sidewalk, on each side of the via.
(G). Umbones or edge-stones.

Today most of the top layer of concrete has eroded, leaving the bumpy looking pavers on top, but at the time, these roads were smooth and fast.