For the technically minded: How bus priority in Swansea works.
There have been some reports in the media over the last few days about bus priority in Swansea. Not all of the reports have been totally accurate.
Here, for the technically minded is how it works, or will work once our Ticket machines are hooked up to the network:
Signals in central areas, including Mumbles / Oystermouth Road and Fabian Way have been upgraded to IP based communications over a number of years using a mixture of mesh wireless, ADSL and 3G/4G. This allows the second by second links required to run adaptive signal control. Signals run under the control of the SCOOT (Split Cycle Offset Optimisation Technique) system, this is essentially a computer model of the network. Using buried loops to measure vehicle numbers, flow data is fed into the system, which automatically adjusts green times, cycle times and offsets between junctions to keep overall delay to a minimum.
More isolated sites run under vehicle actuated (VA) mode where a junction will cycle round in stage order and run any stage where a demand exists up to a pre-set maximum green time.
This scheme has involved the provision of new communications equipment for other strategic corridors, Carmarthen Road, Llangyfelach Road, Cockett Road and Gower Road. The VA junctions are also being upgraded to MOVA (Microprocessor Optimised Vehicle Actuation), this uses detectors on the approaches to measure vehicle flow and saturation, and will vary green times based on how saturated an approach is. This will offer a typical improvement of around 20% for all users.
Bus priority has been around in Swansea since the late 70s, and generally utilised buried detectors and bus mounted transponders. A bus passing over the detector would input a priority demand, this would be handled differently depending on the method of control, and could either be an absolute priority demand, where the signals would immediately cycle to the required stage, an extension if the junction was already on the required stage to hold the green on for the bus, or implemented through SCOOT, which would either shorten or skip stages to get to the bus more quickly.
The biggest issue with this kind of priority is that it took no account of whether the bus actually needed it.
The late bus priority uses virtual trigger points (geo fences), and if the vehicle is behind timetable signals in front of it can be adjusted to smooth the vehicle’s passage to try and get it back on schedule.
First Cymru have been rolling out the Ticketer system onto their local fleet over the last few months. They also use this for monitoring bus positions and timetable compliance. A data feed from this system is fed through some adaptor software into a common database. The common database is a means to use data from previously disparate systems to affect what each other do. Swansea Council’s common database links Urban Traffic Control, Car Park monitoring, pollution monitoring, count sites, variable message signs and soon Ticketer.
An output from Ticketer will, via the common database create an input into the urban traffic control system to request an alteration to the signal timings.
Although this is the first time Ticketer has been used as the bus monitoring system, similar systems have been used elsewhere.
The scheme is packaged up into 3 parts:
1. Communications infrastructure.
2. Enhanced junction method of control (which helps everyone).
3. Late bus priority ( which only helps the vehicles which need it, and represents a much softer approach to bus priority in order to minimise adverse effects elsewhere).
- so now you know!