DTA simulation with reduced number of iterations


An iterated (day-to-day) dynamic traffic assignment (DTA) is considered. In each iteration, a certain fraction of the totaltravel demand adjusts its travel pattern before the entire demand is loaded onto the (congested) network. It is assumed that thedemand is composed of at least two commodities that exhibit non-identical travel behaviors. The demand changes from oneDTA iteration to the next can then be decomposed into two components: (i)demand exchangesbetween commodities, whichdo not affect the total (aggregate over all commodities) demand pattern, and (ii)demand shifts, which do affect the total demandpattern. Given that there are many (day-to-day) sequences of demand and congestion patterns that lead to the same stationaryassignment, the approach taken here is to minimize congestion variability along this path by favoring, to the extent possible,demand exchangesoverdemand shifts. The underlying intuition is that the resulting reduction in congestion variability andconsequently better predictability of travel times leads to a faster and/or more stable convergence of the assignment.

The selection of replanning rates in general-purpose DTA simulation packages has, due to the limited tractability of suchsystems, received limited attention in the literature. In deterministic settings, flow averaging schemes according to (variantsof) the method of successive averages are often considered (Liu et al., 2007). In stochastic process assignment, constantreplanning rates may be preferred because these can lead to unique stationary process distributions (Watling and Hazelton,2003). The possibly interesting twist of the approach described here is that it (i) leaves the choice of a global replanningrate (being identical for all commodities) to any available algorithm or expert and then (ii) accelerates the convergence of thesimulation process by deriving commodity-specific replanning rates. Lu and Mahmassani (2007) and later Lu et al. (2009)pursue the same line of thinking but make more specific modeling assumptions (a route swapping assignment that aims atattaining a deterministic user equilibrium) than what is assumed in the subsequently described method.



Lunch seminar in transport economics

Professor Stef Proost, KU Leuven presents "What Role for Electric Vehicles in Decarbonizing the Car Sector in the EU?"

European Road Profile User's Group, ERPUG

Welcome to the sixth ERPUG meeting in Vilnius, Lithuania. 

ICTTP 2020

ICTTP, International Conference on Traffic and Transport Psychology, is held in Gothenburg, Sweden.



VTI’s simulators are being used for emergency vehicles

Better accessibility and shorter response times for emergency vehicles – this is something that standardised, directed, traffic messages, transmitted over the 5G network can contribute. Within the EU project Nordic Way 2, a functioning prototype of such a...


Modal shift - a way to achieve the environmental objectives

Shifting freight transports from road to rail and water can contribute to achieving the Swedish environmental and climate objectives by 2030. How this could be done is something that VTI researchers and researchers from Gothenburg University are investigating...


Report regarding government commission on the costs of traffic to society has been submitted

Since 2013, the Swedish National Road and Transport Research Institute (VTI) has had several government commissions to produce documentation on the costs to society caused by traffic. On 1 November 2018, the agency reported its latest commission, Samkost 3....


International standardisation efforts have many advantages

VTI participates in several international standardisation committees. The work is important because it helps to ensure that standards can be adapted to Swedish conditions and it also provides access to valuable contacts and networks.


China wants to work with the best

Through the CTS cooperation, VTI is gaining valuable research contacts with China. The country is facing major challenges in the field of road safety but also has enormous potential.


VTI participated in conference on electric roads

Systems with electrified roads are a relatively new concept and many projects have been launched in recent years. To stimulate the transfer of knowledge and collaboration, the Research and Innovation Platform for Electric Roads arranged its second...