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Microprocessor Optimised Vehicle Actuation (MOVA) is an adaptive traffic control system developed to overcome some of the problems associated with more traditional systems of vehicle-actuated traffic signal control. It is very similar in its operation to SCOOT except that it is intended more for isolated or small linked networks of junctions.

The problem with traditional vehicle actuated systems

Since WWII, Vehicle Actuation (VA) had become the standard form of traffic light control at isolated junctions in the UK. Although VA has considerable benefits over previous fixed-time systems, in that the green light is only displayed only when traffic demands it, and for as long as actually needed, there are several deficiencies that come with it.

Most notably, its decisions to extend or end the green light do not consider the queues waiting at red signals or upstream approaching traffic, which sometimes results in unnecessary delays.

It also places a burden on the traffic engineer, as the maximum green times have to be frequently adjusted to match with the prevailing traffic conditions. This is often not done, leading to less than effective operations.

On high-speed roads, additional detection equipment has to be installed, in order to reduce the likelihood of vehicles getting trapped in the "dilemma zone" when the traffic signal changes. They provide an additional extension period, which varies depending on the speed of the vehicle. At particularly busy sites, this detection equipment becomes ineffective, as stages often end up running to the maximum, causing the signals to change regardless.

For these reasons, the TRL in the mid-80s developed a control system intended to overcome these problems, MOVA.

How it works

At the core of MOVA is the MOVA kernel, which is a development of the SCOOT kernel with some adaptations; this is usually a software package that sits within a separate unit, although the Microsense/Telent controller has the software "built in" to the main controller CPU.

MOVA takes traffic flow information from detectors in each traffic lane on the approaches to the junction. The detectors are usually placed at 8 seconds and 5 seconds distance from the stop line - known as the "IN" and "X" detectors respectively - although this can be adjusted if necessary to cater for site conditions.

MOVA has two modes of operation:

"Delay Minimising" is the normal mode of operation, which will hold a green signal for approaching vehicles when the junction is not busy and it is more efficient to keep a particular stage at green to keep approaching vehicles moving than to run a competing stage. VA, on the other hand, would've simply changed the signals as soon as the gap between vehicles exceeded the extension setting.

"Capacity Maximising" is the other mode: it runs when a junction gets busy, such as at rush hour, and will cut a stage green when the saturation flow on a particular arm of traffic drops below optimum - i.e. when traffic starts to gap out - and it is more efficient to run a competing stage, to get as much traffic through a junction as possible.

Before installation

It is important that prior to the MOVA installation, the cruise speeds of vehicles approaching the junction are measured, to ensure that the detectors are installed at the right locations. The traffic engineer will then create a "MOVA dataset" which will be uploaded to the MOVA unit and initialised on site.

After installation

Following the installation of MOVA the traffic engineer will then carry out a validation exercise, which will fine tune the MOVA dataset to ensure that MOVA works effectively. The aim is to ensure that MOVA works in both ... '(text missing?)'

What are the benefits?

MOVA is an adaptive system. As such it can respond quickly to changing traffic flows and is not affected by time of day or day of year; it relies solely on traffic flow information from the detectors and because of this it solves many of the problems facing the traffic engineer as road networks become busier.

The MOVA kernel is in many ways more adaptive than SCOOT, as SCOOT is more concerned with the efficient and stable operation of the network, whereas MOVA is concerned with only its junction (or neighbouring junctions if running linked MOVA). Thus while SCOOT is slower to respond to changing flows and can sometimes appear to hold a traffic stage at green injudiciously, MOVA adapts on a per-cycle basis and can raise and lower the cycle time almost immediately.

That is not to say that MOVA is better than SCOOT as both systems offer benefits to the road user; to flood a network with traffic in the way that MOVA could do would be terribly disruptive and in some circumstances may lead to oversaturation downstream in the network. SCOOT avoids this by making slower decisions and drip-feeding traffic in to the network in a more controlled fashion.

The future

The signal companies are now offering combined MOVA and UTC units, which allow both SCOOT and MOVA to run on a site in accordance with the traffic engineer's wishes. This gives the responsible highway authority increased flexibility in the operation of its network by allowing it to run SCOOT when co-ordination between junctions is desirable and MOVA when traffic flows are lighter and co-ordination is not of such paramount importance.


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