Figure 1:The Safe System – Towards Zero Foundation

Written by Suzanne Walker, Consultant Engineering – Mirragin

As a transport engineer, one of the key things I always think about, is safety. As a commuter, we generally try to push safety concerns to the back of our thoughts because we rely so heavily on using transportation, but that doesn’t stop them from being there. Now I am not going to mention vehicle collision likelihoods or other scary statistics, because whilst it brings awareness, it doesn’t help us understand how we can improve things.

So I wanted to share some of the safety approaches I have used as a transport engineer, and talk about how these could be applied to advanced air mobility.

Safe systems

Safe Systems is a road safety philosophy that considers kinetic energy exchange in a crash, to determine maximum impact speeds to hopefully avoid death and serious injury.

The responsibility is across road designers, vehicle manufacturers, authorities, and road users, because good design can’t keep you completely safe, low speed can’t keep you safe from other drivers, and unsafe environments make it harder for everyone.

There are four pillars to reflect this:

  1. Safer vehicles
  2. Safer speeds
  3. Safer roads
  4. Safer road users

Sometimes we add post crash response as an honourary fifth pillar, but basically by combining these pillars, we have the best chance for a safer road environment, with hopefully some redundancy.

All of these pillars can be applied to advanced air mobility. Safer roads are safer flight paths, and the rest easily translate, just change the word road. Additionally, it is also good to consider for ground risk – the interaction with vehicles and vulnerable users (pedestrians, cyclists) – there are limits to the kinetic energy they can sustain, and we need to be particularly aware of this when integrating into urban areas due to the increase of exposure (not just operational exposure, but failure, FOD (foreign object debris), etc).

Safe systems assessment

A safe systems assessment evaluates road design projects by looking at existing conditions and proposed conditions, primarily looking at safer roads and safer speeds because that is what is being reviewed. There is an Austroads framework and state guideline if you want to read further.

To undertake this assessment, you identify factors that increase and decrease hazards on existing and design conditions, using exposure, likelihood, and severity to determine the rating, and then make recommendations for how the design score could be raised through design or scope changes. This is organised by identifying factors that influence the risk of the following collision types:

  1. Run off road
  2. Head on
  3. Intersection
  4. Other (Driveways, merging, anything that didn’t fall into other categories)
  5. Pedestrian
  6. Cyclist
  7. Motorcyclist

To apply this to advanced air mobility you could consider things like:

  1. Separation between aircraft and other transport modes including when sharing the same space (road dividers are an example, but at an intersection, you do interact with oncoming traffic)
  2. Clear space without hazards if change from flight path needed to occur (imagine stopping on the side of the road, or losing control and running onto the shoulder)
  3. Angle of approach to other transport modes and conflict points when sharing the same space
  4. Priority and control when sharing the space (such as air traffic management)
  5. Environmental hazards such as standing water, or visibility

Road safety audit

A road safety audit is similar in many ways to a safe systems assessment, again with its own guidelines. These can be done at pre construction, during construction, and post construction which also includes existing roads regardless of when constructed. The audit is looking for safety deficiencies but does not follow a matrix style assessment.

As for a safe systems assessment, the earlier in a project that a safety audit/assessment is conducted, the easier it is to change the design to make improvements – which is why now is a fantastic time to start talking about it for advanced air mobility.

Traffic behaviour analysis

The final approach that I want to share is traffic behaviour analysis. This is an area that provided my first connection to drones – I helped integrate video collection via drone of traffic at an intersection. Again, an area that many discussions could be based around, but the purpose for this article, is to comment on the benefits of analysing how the actual traffic behaves.

You can record vehicle speeds, volumes, lane positioning, near collisions, turning behaviours, etc. As much as the above assessments are great, it relies on the engineer to have the innate knowledge of traffic behaviour and hope the site inspection conducted shows typical behaviour to inform the safety assessment.

As I am sure you have experienced, people don’t always use the road environment as designed – maybe they speed, maybe a single lane is wide enough and has become a pseudo two lane, pedestrians might cross in non-defined locations or not wait for the green light. This comes back to the road user pillar. Even the best design cannot ensure conformance, and in transport, we know to design for this. For example, at an intersection, where the rest of the road is divided, you still include the chance of someone driving down the wrong side of the road. Road safety is not just for those who follow the rules perfectly, we want to keep everyone safe. In that same vein, hobby drone operators have been known to not follow all of the rules, maybe even not-so-hobby operators.

So a few thoughts to leave you with:

  1. Safer roads (flight paths) and safer speeds should be considered for advanced air mobility for interaction with other advanced mobility, as well as other transport modes
  2. Vehicles, pedestrians, and cyclists can’t withstand much kinetic energy, and close integration means we need to consider how to keep them safe
  3. Investigate how people actually behave, and realise it can change over time
  4. Don’t design for compliance, design for the best safety
Written by Suzanne Walker, Consultant Engineering – Mirragin

Suzanne is an experienced engineer with a passion for problem solving, leadership, research informing best practice, and making a positive impact. She has a wide range of multidisciplinary experience, across traffic, rail, major road infrastructure projects, OEM manufacturing, STEM research, and project management. Suzanne started with Mirragin in January 2022 and is now working with drones, autonomous systems, and AI. Suzanne is also undertaking a PhD exploring how community knowledge can be implemented better in engineering projects to improve design outcomes.