Which of the following is not a type of traffic assignment?

• A. All-or-nothing
• B. Minimum travel time
• C. Gravity model
• D. Capacity restrained

Answer: (C)

The gravity model is not typically classified as a type of traffic assignment. In traffic engineering, traffic assignment refers to the methodologies used to allocate traffic flow to the various routes in a transportation network.

The all-or-nothing assignment distributes all traffic between an origin and destination to the route that has the least travel time, without considering congestion effects. This method is straightforward and useful for the initial phases of planning but can be overly simplistic.

Minimum travel time refers to a similar concept, where the assignment process aims to minimize the travel time for vehicles based on the different routes' conditions, which include traffic congestion and other factors.

Capacity restrained assignment, also known as a stochastic or constrained assignment, considers the capacity of the roadway when distributing traffic, thus acknowledging that roadways have limited capacity and traffic may experience delays due to congestion.

The gravity model, on the other hand, is a method often used to anticipate travel demand based on the interaction between different zones, akin to how populations and attractions might interact, rather than being a method for assigning traffic flow on a network. This model serves a different purpose in travel demand forecasting rather than the actual assignment of traffic flow on a set network.