Here is a quick guide about how to interpret g-force, braking, and acceleration graphs.
Tip: The broader traffic context (i.e., road infrastructure, traffic calming measures) should always be considered when interpreting G-force, Speeds, and Braking/Acceleration to determine whether the data output matches known acceptable thresholds at certain speeds.
How to interpret G-force graphs
The G-force movement graphs maps harsh steering and harsh braking movements performed by drivers.
The equation for relational G-force is:
$Relational \space Gforce = \sqrt{x^2 + y^2}$
Where x = acceleration and deceleration, and y = left and right steering. Based on American research, g-force values can be labelled as:
- Harsh braking when G-force value is > 0.6
- Harsh acceleration when G-force value is > 0.4
- Harsh swerving when G-force value is > 0.47
Example: G-force movements
The graph below shows drivers performing a right-hand turn on the A4 Western Distributor travelling towards the Anzac Bridge in Sydney.
As drivers go around the bend, there is an exit ramp. When this ramp is congested, it leads to back spill into the left-hand lane on the Western Distributor. This causes drivers to swerve to the right to pass these vehicles and brake harshly. This example highlights that a number of vehicles were experiencing high G-forces of above 0.4, with some high G-forces happening at high speeds.
Keep an eye out for speed on the selected roads to determine whether a G-force event is contextually appropriate for the traffic conditions.
How to Interpret Speed vs Braking and Acceleration graphs (Previously X-axis)
Speed vs Braking and Acceleration graphs show acceleration and deceleration at different speeds. A positive g-force value means that a vehicle is accelerating, whereas a negative value means that a vehicle is decelerating.
Example: Braking and Accelerating
The graph below shows drivers performing a strong right-hand turn on Moss Vale Rd in the Kangaroo Valley, NSW.
From the graph, we can see that most drivers are decelerating as most of the data shows negative g-force values. Although there are instances of more severe braking or acceleration, the majority are non-violent instances, occurring at speeds below 50km/h
How to Interpret Speed vs Steering Graphs (Previously Y-axis)
The Speed vs Steering graphs show steering or swerving at different speeds. A positive g-force value means that a vehicle is moving towards the right, whereas a negative value means that a vehicle is moving towards the left
Example: A strong left-hand turn
The graph below shows drivers on a very strong left-hand bend on the Cahill Expressway on-ramp in Sydney.
It shows a cluster of instances where vehicles are making a violent left-hand turn at higher speeds than the posted sign limit and experiencing g-forces of above 0.5.
How to Interpret Braking & Acceleration vs Hour of Day
The braking and acceleration vs hour of the day graphs show
Example: A strong left-hand turn
The graph below shows drivers on a very strong left-hand bend on the Cahill Expressway on-ramp in Sydney.
It shows a number of particularly high g-force readings associated with harsh acceleration (i.e., g-force of 0.47 and above) occurring at 6am, 12pm, and 3pm, whereas there was some evidence of particularly harsh braking occurring at 8am.
How to interpret Steering vs Hour of Day
The steering vs hour of the day graphs show a breakdown of harsh steering by hour of the day.
Example: A strong left-hand turn
The graph below shows drivers on a very strong left-hand bend on the Cahill Expressway on-ramp in Sydney.
It shows a number of particularly high g-force readings associated with harsh left-hand steering (i.e., g-force of 0.47 and above) occurring at 9am, 3pm, 10pm, and 11pm.
