Transport planning experts Brian Smith and Mohammed Islam discuss how undertaking effective field trials of transport interchange or terminal layouts and incorporating the results into designs can help to resolve operational or design issues.
After all, it is almost always humans that will be driving the vehicles we are designing for and while swept path diagrams and bus and other vehicle models in CAD packages provide detailed guidance on the capabilities of vehicles and the space they need to manoeuvre, they cannot take into account the different ways human drivers respond to design characteristics, and the movement of other vehicles.
A particular problem in complex transport terminal and interchange design can be that a CAD operator can easily make a vehicle manoeuvre on the screen in ways which would be beyond the capability of a human driver.
Figure 1 below shows an example of this in a bus terminal design assessment. Here, CAD swept path analysis is used to demonstrate the suitability of a design, but successful manoeuvres appear to depend on multiple precise and immediate manoeuvres which may be beyond the capability of a bus driver of average abilities.
Figure 1: Example of this in a bus terminal design assessment
CAD-based swept path analysis can sometimes fall into a trap whereby the swept path analysis is used to show that a design can work, rather than being used to inform design as it progresses. The temptation is to fit the swept path into the design by having the program manoeuvre the vehicle in unrealistic ways, or by varying parameters like vehicle speed and lock to lock time.
Designs developed this way run the risk of failure in operation, with potential for conflicts between vehicles, and crashes. Field trialling can be valuable in both establishing design parameters for CAD packages at the outset of design, and confirming the feasibility of designs prior to construction, particularly where operation of the planned facility may involve interaction between vehicles and use by drivers of varying skill levels.
Many design guidelines for transport terminals and interchanges adopt conservative dimensions for things like bus stop lengths and carriageway widths, often adopted from guidelines intended for use in mixed traffic; and application of these can result in over-generous space requirements, especially in off-street facilities. There are benefits to making transport terminals and interchanges more compact and space-efficient, both in terms of capital and operating costs for infrastructure providers, and legibility and personal safety for customers. Field trialling can confirm the appropriate design standards to use to reflect the situation, vehicle fleet and level of demand, and help to define the most compact and workable solution.
The main objective of field trialling transport terminal and interchange layouts is to confirm and validate CAD testing – the results of the trial are fed into the design process, allowing CAD swept path analysis and identified critical dimensions to be undertaken in confidence that they represent real world operations (ground truth).
However, there are some substantial additional benefits that can justify undertaking field trials, including:
Generally, not all of a transport terminal or interchange needs to be trialled. Rather, critical areas should be identified for field trialling, including areas requiring critical manoeuvring, areas around entrances and exits, merging and crossing points or areas where vehicle interaction, or design elements introduce complexity.
Choosing the trial site
Field trial sites need to be of sufficient size to accommodate the designs to be tested, as well as the associated vehicle movements, marshalling and access; and trial staff and observers; and should be primarily level, sealed and without physical objects which could impede vehicle movement. Ideally, the site should be vacant, unused or able to be segregated from conflicting activities during the test period.
As an example, three recent bus station field trials we have been involved in took place at the disused Wigram Airbase aprons in Christchurch New Zealand, a disused runway at Ardmore Airport, Auckland, New Zealand; and about 30 per cent of the Red Bus depot in Christchurch New Zealand – all large sites and unused at the time (Red Bus reorganised depot parking to make the area available).
Timing and duration
Vehicle availability is a key influence on the timing of field trials. For bus facilities, the best time is generally between the end of the weekday AM peak period and the beginning of the afternoon school peak period, when bus availability is high.
Layout and Set-out
Field trial set-out is undertaken by a survey team prior to the field trial, so that drivers, the field trial team and observers can understand and navigate the concept layout.
There is an art to setting out the concept layouts to be trialled on the trial site. As much as possible 3D elements (such as columns and kerblines) should be represented in addition to 2D markings, as these elements can be important influences on driver behaviour.
Personnel required to undertake an effective field trial include:
Safety should be the highest priority in the field trial. It is the controller’s role to manage vehicle and pedestrian movements and avoid conflicts and crashes; and to ensure the trial proceeds in a safe manner.
Depending on the location used for the trail, additional liaison with the site operator may be required in order to establish site specific risks. For example; if a disused airport runway is to be used this could form part of an operational airfield which may have less apparent safety risks in the event of an emergency.
A range of data should be collected during the course of the field trial; and at its conclusion. These include:
A debrief of trial participants (ideally on the site) can help to highlight trial findings and issues experienced and agree design refinements or further testing.
Briefings and familiarisation
A detailed briefing for field trial participants and observers is an important starting point, describing the project, the field trial’s part in it as well as the concept layout to be tested, as well as the participants’ roles and safety procedures.
We are interested in observing the behaviour of drivers and vehicles from the normal operation of the facility concept design we are testing, so some time should be allocated at the commencement of the field trial for drivers to become familiar with the layout before observations are recorded.
In general, a handful of passes through the concept layout will be necessary before drivers become familiar enough with the layout so that valid observations can be made.
The objectives of field trial observations should be to record the performance of vehicles and drivers and identify any requirement to modify the concept layout, or the need for management measures (such as line marking, signage, ITS and the like) to address potential conflicts or other issues.
The results of the trial should also permit the validation of parameters in CAD designs and bus swept path simulations, to enable design development to proceed with confidence.
Observers should observe and record in real time, vehicle performance and layout deficiencies, based on simple directions to drivers.
Observations of vehicle transit times and times for different activities or functions can be captured from video records post-trial.
Manoeuvring performance should be documented by marking vehicle positions (swept path extent, wheel tracks etc) during the manoeuvres with pavement paint and/or GPS marker, (ensuring that recording does not affect the manoeuvres being undertaken). For example, traffic cones may be relocated to optimise the layout’s operational performance – it is important to capture those modifications for design documentation.
Any modifications to concept layouts undertaken during the trial (relocation of indicative kerblines, traffic cones, temporary fencing etc) to resolve operational or design issues should be recorded on GPS to allow plans to be updated.
It is important to recognise that the field trial layout will differ from a real-world facility (it generally won’t be possible to perfectly replicate the final facility being tested) and so field trial testing and observations should take into account the lack of some design and physical elements that can influence driver behaviour, as well as potential driver difficulty in interpreting the trial layout consistent with real-world situations. Put simply, it may be more difficult for a driver to negotiate a trial layout than a permanent layout in the real world. Experience will show which design elements of a trial layout are critical to driver behaviour or effective operation of the facility, but drivers’ difficulty in negotiating some parts of a trial layout could reflect the artificial environment of the trial more than design deficiencies.