With Podaris, you can use parametric modelling to create different kinds of transport infrastructure. These LayerTypes capture both the physical and operational aspects of their respective types of infrastructure, ensuring accurate right-of-way and travel-time calculations.
When creating a project, you can specify a default LayerType. This should be the dominant type of infrastructure that your project will be modeling. This does not limit you in any way: multimodal networks can be created by adding new layers with different LayerTypes.
Parametric modelling process
Each LayerType contains detailed parameters concerning velocity, acceleration, and jerk tolerances of its respective infrastructure system. This is used to create a velocity profile for every part of the project, which is then used for the travel time and isochrone calculations.
There are two distinct elements to the parametric modelling:
Geometry balancing -- By default, Podaris attempts to create infrastructure paths that are first as fast as possible, and second as straight as possible. This satisfies the usual requirements of planners and civil engineers, and results in curve radii that are as large as required while maintaining full velocity, but no larger. If this is not the optimal solution for a given location, then additional constraints can be added by selecting points and adjusting the min/max radius constraints.
Velocity profiling -- Podaris assumes that the system will aim to operate at the maximum possible speed, given lateral accceleration limits around curves, stopping times at stations, and acceleration / deceleration times around both curves and stations. Additional maximum velocity constraints can be set on both points and lines. (It is not possible to set minimum velocity constraints, as the velocity profiling already maximizes velocity by default, and any additional velocity would create overspeed conditions.)
Supported Infrastructure Types
Personal Rapid transit (PRT)
Personal Rapid Transit consists of autonomous, demand-responsive vehicles running on custom segregated infrastructure. Several companies offer market-ready PRT systems, although the characteristics of each system differ somewhat.
In Podaris, the PRT LayerType is based on the "most common denominator" properties of the market-ready vendors, as measured by those that are part of the Advanced Transit Association Industry Group. This produces a "common envelope" that any of the market-ready vendors can operate within, suitable for vendor-neutral early-stage feasibility studies. In the future, Podaris will be working with individual vendors to model their specific technologies more exactly.
Sample PRT projects -- feel free to clone these to produce your own modifications:
(Note: PRT networks generally require stations to be modelled on sidings rather than on the main guideway. In Podaris, this should be done explicitly. If stations are placed directly on the main guideway, the boarding/alighting delay will interrupt the thru flow of traffic, leading to inaccurate travel-time calculations.)
This LayerType represents grade-separated heavy rail infrastructure.
(Note: This LayerType is still in beta. Because scheduled services are not yet modelled, travel-times will assume zero wait at stations, and zero transfer time between lines.)
(Note: This LayerType is still in beta. Because scheduled services are not yet modelled, travel-times assume zero wait at stations, and zero transfer time between lines. Furthermore, Podaris does not yet model accurate curve transitions as clothoid curves, which for a high-velocity system such as the hyperloop may result in a meaningful offset of the track.)
(Note: This LayerType is still in beta.)
Group Rapid Transit
The kinematic calculations of Podaris' solver are highly accurate, but several limitations should be kept in mind:
- Podaris treats layers as 2-dimensional planes. If the velocity should be affected by gradients, this will not be automatically accounted for. This can be manually compensated for by setting velocity constraints on individual points and lines.
- Curve transitions are not yet accurately drawn with clothoid spirals. This is only significant in higher-speed systems such as high-speed rail or Hyperloop, so these right-of-ways should be considered as more indicative.
- Tight curves may require a wider right-of-way, due to swept-path considerations, particularly with longer vehicles. Swept-path calculations are not yet part of Podaris.
These limitations will be addressed in forthcoming versions of Podaris.