Articles
Construction phasing – Modelling Assessment
Have you thought about modelling construction phases and if not why?
BSTC has been working with Kirklees Council to deliver the A62 Smart corridor as a key UTC representative.
Key
Red Circle – signalised junction part of the scheme
Yellow Highlight – Scheme extents
Purple Highlight – affected network
During my time delivering the project I had to regularly manage and monitor the network to ensure disruption was kept to a minimum. Five key junctions were directly affected by the works but during the building process the disruption had a wider impact on the rest of the network.
During the construction I regularly had to model junction in isolation to assess the effect of changing temporary signal layouts. In particular, the SRL Urban 64 junction which managed five arm junction from a gyratory layout to a crossroads plus T-juncton as the final layout. This required four construction phases to facilitate the building which meant four different layouts / operations.
This got me thinking: Why are we not assessing the impact of construction in Microsimulation prior to delivery?
The local authority has an obligation to mitigate network congestion as much as possible. Generally, contractors will look to provide the cheapest option rather than one which provides a balanced solution. Should we specify in major projects that the contractor should look to provide evidence which shows the network disruption would be kept to a minimum? We often modelling the base situation and final scheme, but we never look at the construction which can often be 12 months or more… would this then give the Council confidence that the construction disruption would be kept to a minimum? And can should this to key stakeholders and give assurance to the general public?
MOVA – Lane Specific linking
MOVA linking is often adopted at signalised roundabout when an external approach such as a split road requires co-ordination to the next conflict point on the roundabout allowing for progression. Linking is often driven from a special phase either when are green or from the leaving amber to ensure co-ordination.
When validating a site below which consists of a two-lane approach and two-lane internal arm on a typical four arm signalise junction, due to the nature of the lane marking and movement there was a performance advantage to be gained. It was observed during the validation process that on the slip road the left lane went left (shown in Red), and the right lane went ahead and right around the junction (shown in Green). Resulting in only the right lane required linking to the next stream the left lane would exit the junction. What would happen is the linking would hold on when traffic was on the left lane rather than right lane, resulting in any traffic waiting on the conflicting approach (shown in Yellow) would be sat waiting with no traffic passing them.
The solution, change the linking to only be active when traffic was in the right-hand lane, this was done through special conditioning in the controller which looked for extensions on the right hand lane stop line.
Results
To understand the impact of the change in terms of performance occupancy data was collected which shows the average time the X loops are occupied while at Green. The higher the value the slower the vehicles crossing the X loop the great the queue.
MOVA Validation why?
Microprocessor Optimised Vehicle Actuation (MOVA) is deployed at around 30% of all traffic signals in the UK which is estimated to be around 10,000 signal junctions/crossings. MOVA validation, which is the process where the dataset and all the parameters it contains, is adjusted to the current traffic conditions to maximise the junction performance through the MOVA algorithm. Traffic conditions change across the UK in a dynamic environment it is essential MOVA validation takes place every few years to ensure the junction is operating affectively.
To maximise the assets, it would be advisable that the junctions are validated by the asset owner and budget is set aside. Money allocated into the asset can be a very good investment, for example:
Example:
A motorway junction was causing congestion, which lead onto an exercise which resulted in a major infrastructure scheme being put forward to mitigate the congestion with the value of several million pounds. However, it was suggested that the junction operation should be reviewed by a competent MOVA specialist to ensure the junction was operating affectively. During the review and validation, the junction operation was found to be running sub-optimal and through adjusting the MOVA parameters and dataset (software) the congestion was mitigated. This situation is very common due to the lack of MOVA specialist within the country and even more difficult in precuring their services being either one-man companies or small SMEs. Therefore, it can be estimates than only around 20% of the MOVA junction in the UK are validating correctly leaving 80% of the network running at sub-optimal performance.
This highlights that maximising the current technology on ground should be the first point of call and not infrastructure projects. A simple MOVA validation worth only a few thousand saved the asset owner a few million. In benefit cost ratio terms these were figures of 40+ verse 0.2 from an infrastructure project. It would be recommended that budget be set aside to validate these sites to maximise network performance as part of the annual network management programme.