Background and Project Objective

The “Guidelines for the Design of Rural Roads (RAL)” (FGSV 2012) distinguish between four design classes (EKL) with regard to design standards. Rural roads in the second class EKL 2 serve as interregional connectors and handle a significant portion of national traffic outside the freeway network. Junctions play a particularly important role in this context. This is where traffic flows from different roadways meet and conflicts, delays, and a significant portion of traffic accidents occur. Four-leg junctions are particularly challenging, as significantly more traffic flows intersect at them than at three-leg junctions. This raises the question for planning practice: Under which conditions is which interchange or intersection type and regulation appropriate? 

The goal of the project is to identify suitable applications for four-leg junctions on EKL 2 roads. The focus is on determining which types ensure both safe and efficient traffic flow under which traffic volumes and boundary conditions. 

Approach

Within the scope of the project, the two central evaluation dimensions - traffic safety and traffic flow - are considered together.

• Traffic safety at four-leg junctions of various types
• Traffic flow and traffic quality at the junctions
• Travel times and delays at junctions
• Impact of junction design, traffic volume, and traffic control on traffic quality

The Chair of Transportation Planning and Mobility focuses on the analysis of traffic flow. To this end, an extensive measurement campaign was conducted at rural road junctions in several Federal States. Using automated number plate recognition before and behind the junctions, travel times can be precisely determined and resulting delays calculated. These delays serve as a key metric for evaluating junction types. They allow for a direct comparison of the effects of different junction configurations and regulations on traffic quality and realistically reflect the impact on road users.

The results regarding traffic quality are combined with findings on traffic safety. This creates a sound basis from which recommendations can be derived for the use of four-leg juctions on EKL 2 roads, taking into account both the safety and the capacity of the rural road network.

Project Leader:

• Dr. Matthias Zimmermann (Department of Road Design and Operations, Karlsruhe Institute of Technology, KIT)