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 total travel demand adjusts its travel pattern before the entire demand is loaded onto the (congested) network. It is assumed that the demand is composed of at least two commodities that exhibit non-identical travel behaviors. The demand changes from one DTA 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 and consequently 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 replanning rate (being identical for all commodities) to any available algorithm or expert and then (ii) accelerates the convergence of the simulation 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 at attaining a deterministic user equilibrium) than what is assumed in the subsequently described method.



Social sustainability and just mobility

Welcome to a research workshop on Social sustainability and just mobility, 8–9 October 2019 in Linköping, Sweden

European Road Profile User's Group, ERPUG

Welcome to the sixth ERPUG meeting in Vilnius, Lithuania. 

Vision Zero for Sustainable Road Safety in the Baltic Sea Region

The second Vision Zero for Sustainable Road Safety in the Baltic Sea Region conference will be held in Tallinn, Estonia. VTI is part of the programme committee. 



Knowledge in the fight against microplastics from road traffic

The Government has commissioned VTI to develop and disseminate knowledge regarding the emission of microplastics from road traffic.


How to make autonomous vehicles coexist with other traffic

The road infrastructure must be prepared for self-driving vehicles – especially in the beginning when the concepts are still new. Researchers are contributing to this through CoEXist, an EU-funded research project in which VTI participates as the largest...


Electric roads: ‘Standardisation is an important factor for a future European transport system’

VTI employees recently arranged a workshop in Brussels on the standardisation of Electric Road Systems (ERS). ERS has become increasingly relevant as a possible method for reducing the transport sector's environmental impacts, especially in terms of climate...


Research on passenger and freight transport research

Shift2Rail is a European railway project that works actively to create innovations within the railway sector. IMPACT-2 is a project within Shift2Rail that follows and evaluates the innovation projects. How are the innovations coming along? Are they beneficial...


How vehicles can avoid accidents on newly paved roads

Friction is an important property for road safety. VTI has investigated how roads change in the first few weeks after surfacing work has been completed. Researchers recommend posting warning signs when the road is opened and waiting at least three weeks to...


VTI contributes to study on older drivers and accidents

On behalf of and in collaboration with the Swedish Transport Agency, VTI has carried out a study of older drivers and the link between illness and traffic accidents. The Transport Agency has now published the results.