1.Introduction to highways: The highways are one of the four major modes of the transportation i.e Airways, Waterways, Railways and the Highways. It provides us flexibility of the routes, vehicles, lanes, and time which other modes of transportation lack. Highways have specific characteristics of their own. The highways are used by a number of vehicles, two wheeler, three wheeler, four wheeler etc., but other modes do not have such flexibility. Highways provides the alike service to one and all. You start to travel at your door and you can reach the other end of the doors by highways but it is not same in other modes of transportation. 

Highways also act as the feeder system to other modes of transportation, you have to take a taxy or bus to reach to the Airport, Railway station or harbor. So it is very important mode of transportation. The techniques which we use today to construct the roads are the product of some great minds. The roads are constructed today to withstand all the traffic loads, are very new. 

1.1 History of the Highways Engineering:

1.1.1 Pre-Christian Era:  Initially there was no vehicle, so man used his feet to walk on the earth surface, but after the invention  of the wheel he created the animal drawn vehicles. A need to construct a hard strata arised, so there are some traces of the historical roads which were used by these animal carts. According to historical records, the oldest roads are reported in the Mesopotamia in 3500B.C.  There are no technical details available for them. The roads which are still there and whose technical details are still available to us are the Roman Roads. These roads are constructed at the starting of the Christian era. 

1.1.2. Roman Roads:Romans constructed their roads radially outward from the main city centre in a straight path, no matter the rise or fall of the gradients. The thickness of the roads varied from 0.75m to 1.2m at different places. First of all the hard strata was reached by excavating the top loose soil. The trench of the required width of the road was created. On both edges of the trench a kerb stone of the required height is kept to stablize the further material to be put in between them. A layer of the large stone of thickness 10cm to 20cm was laid down with the help of the lime mortar. Above that two layer of lime concrete each of thickness 25cm to 40cm were laid, the first layer formed of larger broken stone aggregate,  and second one of smaller crushed stone aggregate lime concrete. For top surfacing again a layer of larger stone of thickness 10cm to 15cm laid down by the lime mortar was provided. The technique was used for a long time, but it was not economical because the heavy cost does not match the small wheel loads of the animal carts.After the Roman techniques of the road construction the other ones that are noted and which were popular came in the 18th century.

1.1.3 Tresaguet construction: This technique was used by the Inspector General of all the roads and bridges of the France in 1775AD. Pierre Tresaguet(1716-1796) gave the technique of road construction which got popularised in 1775. The main change that he gave to the road construction technique was the reduction in the thickness of the pavement.  The hard strata was reached first and then the large stones of thickness up to 17cm with their larger base in the downward direction, were laid properly to have more stability. The stones were dressed properly and the voids in between them were filled with the small broken stones, and were tamped thoroughly. The layer of these compacted stones was kept up to 8cm. More smaller stones were used as the surfacing material, which were well compacted to a thickness of 5cm at the edge and increasing gradually towards the center. The shoulders on the sides were also provided with a cross slope of 1 in 45 for their drainage.

The thickness of the pavement was kept only 30cm at the centre, which increased towards the centre to provide a cross slope of 1 in 45. The provision of the slope was for first time with a good reason behind it. It was provided for the surface drainage of the pavement. 

1.1.4 Telford Construction:   Thomas Telford (9August 1757- 2 Sept. 1834) is well known for the establishment of the Institution of the Civil engineers in London in 1818. He provided a new technique for the drainage of the roads. He provided a cross slope in the sub-grade(The bed of the pavement layers) from centre to the edges. It was an effective technique for the drainage of the su-grade layer. 

1.1.5 Macadam construction: John Macadam (1756-1836) is well known for the macadam construction technique. He insisted that there is no need to provide the large stones to take the traffic loads. If the sub-grade is well drained then it can take up the loads easily. He used the mixture of the smaller aggregate stones mixed with some kind of binding material like moist clay. The material is known as the macadam, and it was a good material which still is used at many road constructions.

1.1.6. Modern techniques: After the macadam construction there, were few modification in this technique throughout the world but it was accepted everywhere. The new materials, like bituminous macadam or concrete were also introduced. The term flexible pavement and rigid pavement is used to design the today's roads. There are a number of testing techniques and design methods available now everywhere. 

Today there are so much advancement in the road construction techniques but still if we look back , the history amazes us.

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