Institute for Transport Studies (ITS)

Putting vehicle flow theory into practice

In December, all ITS Masters students were invited to take part in the fourth ITS bumper car challenge in Leeds city centre. They used their knowledge of vehicle flow theory learned in lectures and applied it to this practical experiment. The aim of the experiment was to capture data on traffic flow in a controlled environment and then compare it with the fundamental diagrams for traffic flow on the real road network.

During the first part of the challenge, more than 20 students drove bumper cars around a course whilst Dr Andrew Tomlinson, a member of the Human Factors and Safety group at ITS, collected data about the speed of the cars (metres per second), the density of the bumper car traffic on the course (cars per metre) and the flow of bumper cars passing a point on the course (cars per second).

The number of bumper cars travelling round the course was slowly increased with one car added per lap of the lead vehicle until all bumper cars were driving around the circuit. As the density of bumper cars built up, unstable flow and shock waves were observed and eventually the course became fully congested with a stand still in traffic flow.

Watch a video of the bumper cars challenge in 2017.

The second part of the challenge took place in a computer laboratory back on the University capmpus, where the students analysed the captured data on bumper car speed, denisty and flow. The aim was to construct the three fundamental diagrams of traffic flow: the speed-density diagram, the flow-density diagram and the speed-flow diagram.

The plot below shows data collected regarding vehicle speed and flow from the M62 motorway, and demonstrates the three broad phases of traffic flow: 1 -  Uncongested flow, 2 – Unstable flow, and 3 – Congested flow.

Although the data collected from the ITS bumper cars challenge had many fewer data points, it exhivits similar flow characteristics to that for the M62 as demonstrated by the diagram below, and the three traffic states of uncongested, unstable and congested flow are observable.

The ITS bumper cars challenge is a fun activity with clear learning outcomes and is an innovative and practical application of the knowledge and skills taught during the first semester of the ITS Transport Masters. Student feedback from both parts of the activity was very positive, with reports that it encouraged a deeper understanding of the necessary conditions required for the creation of both shock-waves and traffic jams.