What is the function of longitudinal joints in concrete road pavements?

A longitudinal joint consists of a tie bar placed at the mid-depth of a concrete pavement and it is not intended for joint lateral movement. Then one may doubt the reasons of placing longitudinal joints in concrete pavements. In fact, longitudinal joints are normally designed at a regular spacing e.g.4.5m to accommodate the effect of differential settlement of pavement foundation. When uneven settlement occurs, the tie bars in longitudinal joints perform as hinges (Ministry of Transport (1955)) which allow for the settlement of concrete carriageway. Moreover, it also serves to cater for the effect of warping of concrete due to moisture and temperature gradients by permission of a small amount of angular movement to occur so that stresses induced by restrained warping can be avoided.

Dowel bars are provided in longitudinal joints for the following reasons: (i) In case of the occurrence of uneven settlement between adjacent panels, it helps to maintain a level surface by transfer of loads through dowel bars. (ii) Keep the longitudinal joints close.

Thank you for inviting me, and I agree with Professor Muhammad

a longitudinal joint is nothing more then a joint because of the widthh of the machine. He cannot make more then1 road lane at a time. But they work perfectly with the lateral joints needed for the difference in length due to temperature

Thanks for the invitation.

Wolf and Muhammad said it all. Thanks 

I agree with  MR Kinsbergen

Since the first strip of concrete pavement was completed in1893, concrete has been used extensively for paving highways and airports as well as business and residential streets. There are four types of concrete pavement:

Plain pavements with dowels that use dowels to provide load transfer and prevent faulting,

Plain pavements without dowels, in which aggregate interlock transfers loads across joints and prevents faulting,

Conventionally reinforced pavements that contain steel reinforcement and use dowels in contraction joints, and

Continuously reinforced pavements that have no contraction joints and are reinforced with continuous longitudinal steel.

Endorse  Mr. Muhmmad Shakeel answer.