The following description was taken from Exploring the Road Safety Benefits of Direct vs Indirect Vision in HGV Cabs by TfL :

The aim of this study is to deliver evidence on the implications of mandating cab design to allow maximum direct vision of vulnerable road users. This evidence is required by the European Commission before they consider future regulatory change relating to the design of HGV cabs. To provide such evidence, this study explores:

  • Reaction times to vulnerable road users appearing directly (through windows) vs.
    indirectly (through mirrors).
  • Driver behaviour in relation to vulnerable road users when driving a traditional
    cab vs. a low-entry cab.
  • The impact of additional cognitive processing on reaction times and driving
    behaviour.

This study is comprised of three phases, which each phase informing the design of the next:

  • Phase 1: Literature Review
  • Phase 2: Quantitative surveys of HGV drivers, cyclists and pedestrians
  • Phase 3: Laboratory experiment into the benefit of direct eye contact

The laboratory experiments were designed as follows:
Three Control Experiments took place in simulated low-entry cabs. These experiments were designed to test reaction time to stimuli displayed directly (through windows) vs. indirectly (through mirrors) while stationary and navigating:

  • Control Experiment 1 – Visual Search While Stationary
  • Control Experiment 2 – Visual Search Whilst Navigating
  • Control Experiment 3 – Pedestrian Visual Search Whilst Navigating

Two Main Experiments took place, comparing driving performance in traditional cabs (with increased direct vision) vs. low entry cabs (with greater reliance on indirect vision). These experiments simulated a disproportionately high number of close proximity VRU interactions. This was important to allow us to explore how varying cab design would impact driver behaviour in such interactions.

  • Main Experiment 1 – VRU Interaction
  • Main Experiment 2 – Adding a Distractor Task (adding an additional cognitive task to understand how this impacted reaction times and interactions with VRUs)

These experiments aimed to establish whether there is a safety benefit associated with seeing VRUs directly (through windows), as opposed to indirectly (through mirrors) when driving HGVs.