Common use of Traffic Assignment Clause in Contracts

Traffic Assignment. The state of the practice for highway assignment currently is static equilibrium assignment (Ortúzar and Willumsen, 2011). Equilibrium assignment is an iterative procedure where vehicle trips are loaded to different paths from origin to destination. During each iteration, the trips for each origin-destination TAZ pair are assigned to the shortest path connecting the origin and destination along the network. At the end of each iteration, the travel time on the links making up the path is recalculated based on the number of loaded vehicles (i.e., congestion) on the links. The iterative process ends when travel times along all possible paths connecting the origin and destination become equal. This state is called user equilibrium in that no driver could improve travel time by changing path. User equilibrium assignment procedures are widely available in travel demand modeling software packages. It is generally recommended practice for all areas for highway assignment. In smaller areas, other methods such as all-or-nothing or incremental capacity constraint may be used (VDOT, 2014). 28 states were identified as using the user equilibrium for traffic assignment method. Alabama, Nebraska, and North Dakota applied the all-or-nothing method and only Maine adopts incremental capacity constraint method (NASEM, 2017).