The LOB technique was originated by the Goodyear Company in the early 1940's and was developed by the U.S. Navy in the early 1950's for the programming and control of both repetitive and non-repetitive projects (Turban 1968, Johnston 1981, Lutz and Halpin 1992).  LOB was first applied to industrial manufacturing and production control, where the objective was to attain or evaluate a production line flow rate of finished products (Line of Balance 1962, Johnston 1981, Al Sarraj 1990).

The basic concepts of LOB have been applied in the construction industry as a planning and scheduling method (Lumsden 1968, Khisty 1970).  Several attempts either to modify the basic LOB technique or to develop variations named differently have also been made.  Examples include velocity diagrams (Roech 1972), construction planning technique  (CPT)  (Peer and Selinger 1973), vertical production method (VPM) (O'Brien 1975), linear scheduling method (LSM) (Johnston  1981),  time  space  scheduling  method  (TSSM) (Stradal and Cacha 1982), and repetitive project model (RPM)  (Reda 1990).

LOB has not been fully developed and implemented by the U.S. construction industry because of the immense popularity of network techniques including CPM (Mesyef 1981, Lutz and Halpin 1992).  Even though the development of LOB predates networks, it is safe to state that LOB was not replaced by network techniques but only continued to be seldom used as was the case before the advent of networks (Arditi and Albulak 1986, Tavakoli and Riachi 1990).  LOB has been applied to resource scheduling  and coordination of subcontractors (Levine et al.  1976), to a highway pavement construction project (Arditi and Albulak 1979), to modeling production activities for multi-facility projects (Skibniewski and Molinski 1989), and to transportation projects (Rowings and Rahbar 1992).

The line-of-balance technique is based on the underlying assumption that the rate of production for an activity is uniform.  In other words, the production rate of an activity is linear where time is plotted on one axis, usually horizontal, and units or stages of an activity on the vertical axis.  The production rate of an activity is the slope of the production line and is expressed in terms of units per time.

LOB scheduling can be performed more efficiently when the concept of line-of-balance is combined with network technology.  Usually, a network diagram for one of the many units to be produced is prepared and incorporated into the LOB schedule (Lumsden 1968).

The LOB method manipulates worker-hour estimates and the optimum sizes of crews to generate the LOB diagram.  Worker-hour estimates and optimum crew sizes are usually obtained through direct interaction with a scheduler, the site manager, or related subcontractors who are knowledgeable enough to reflect the actual conditions of a project and of its constituent activities.  Once the number of crews and the expected rate of output have been computed for each activity, the LOB diagram can be plotted.  The number of units to be produced is plotted against time.  Two oblique and parallel lines, whose slope is equal to the actual rate of output will denote the start and finish times respectively of each activity in all the units from the first to the last.

            An attempt to develop a computer application was made by Psarros (1987).  It was limited to solve the basic LOB problem and was not designed to deal with the many implementation-related problems.  This application called SYRUS: A System for Repetitive Unit Scheduling was a pioneering attempt to prove that a computer program can be developed but was not free from flaws.

             The second generation of computer programs was developed by Suh in 1993 and is called RUSS. The system has an analysis program written in "C" language.  The input that consists of several types of initial information is obtained from the user.  The program analyzes a "unit network" that represents the logical relationship among activities performed in one of the many identical units and calculates the production rate of each activity taking maximum productivity and learning effect into consideration. 

CHRISS is a computerized system to schedule high-rise building construction, is developed by using the line-of-balance technology assisted by an expert system. The development of CHRISS provides the opportunity for a novice planner to easily generate a construction schedule for a high-rise building project.  This can be achieved by CHRISS thanks to the knowledge embedded in the expert system module called LOBEX.  LOBEX refers to several knowledge sources of how activities are related to one another (Arditi et al., 2002)