“Conducting case studies from three cities in Utah, USA, we were able to show that better street connectivity is the key – to less travel time and delays, and increased accessibility and safety.”
Combining microscopic and mesoscopic modelling
The project was performed using PTV Visum and PTV Vissim traffic simulation. Traffic modelling of street connectivity benefits consisted of two types of models, mesoscopic models of three community-scale networks (urban, suburban and rural), and three microscopic models of selected neighbourhood networks (campus-type, urban and rural) in Utah, USA. The two types of models were integrated by using the outputs of the mesoscopic models as inputs for microscopic models. The models recorded different levels of traffic performance and measures of effectiveness, such as volumes, vehicle miles travelled, speeds, delays, distances travelled and stops per vehicle.
The result: Several benefits, but also negative effects
We were able to witness several benefits and positive developments: In urban and suburban community-scale networks, enhanced connectivity resulted in a significant reduction in network travel times and delays. VMT on higher-rank streets were reduced as a result of a more balanced distribution of traffic flows within the network. Travel times and delays in the tested rural network were increased, but the traffic volumes and VMT were reduced along higher-rank roads. This is a consequence of different characteristics of a rural network, which generally has higher speed limits and fewer intersections, so introducing new intersections results in increased delays. However, the benefits of a more balanced traffic distribution, as well as shorter travel distances are evident in all community-scale networks.
In the campus-type neighbourhood network we came across more negative effects on traffic operational performance. Here better street connectivity was shown to attract more traversing traffic. However, this does not have to be the rule, since in most cases this will depend on the location of the network and the proximity of high-capacity and high-speed highway facilities, as well as connections to those facilities. Improving connectivity in urban and rural neighbourhoods does not seem to attract more traversing traffic, but it can provide a safer and better environment for non-motorized traffic modes. These benefits are much higher in an urban network because of the overall lower speeds and more intersection with traffic control devices.
The next steps
We found that the integration of the two models from Visum and Vissim is very beneficial in creating and manipulating transportation networks. We have already used the same approach in another project and will continue to do so.