Untangling Notts

Thinking Highways
By Geoff Collins June 18, 2014 16:37

Untangling Notts


In 2012 Nottinghamshire, UK, installed a SPECS3 average speed camera system on the A614, monitoring traffic along 21km of single carriageway road.  The solution was chosen because previous installations of SPECS cameras had consistently delivered improved safety and traffic flows, which were key objectives for this route. Geoff Collins takes up the story two years later.

The A614 is a former trunk road linking the city of Nottingham with the A1.  It is maintained to a high standard and features a wide, single carriageway with several central right turn features into local side roads.  The route has many bends and hills with no footway for most of its length and is one of the busiest non-trunk roads in the county.  Before the SPECS cameras were installed, the A614 had a significant casualty history with 289 people killed or injured in a five-year period.  Nottinghamshire County Council undertook a programme to address this unfortunate record with the support of the–then road safety minister Mike Penning together with the local MP and senior county councillors.

Technology

The A614 is monitored by a SPECS3 POD (Portable Outstation Device) installation, supplied by Vysionics.  Blue SPECS camera columns each hold two SPECS3 cameras, with one camera monitoring the Northbound and the other monitoring the southbound traffic.  These two cameras are connected back to a roadside cabinet, containing a SPECS3 POD.  The POD contains a 3G SIM card that wirelessly communicates back to a remote ERCU (offence server), located at the Nottinghamshire Police offices.  Because the A614 is mostly an unlit road, a number of infra-red (IR) lighting columns were installed; this allows the capture of a well-defined image on a completely dark road.

Speed Monitoring

The primary purpose of a SPECS installation is usually to manage vehicle speeds, thus reducing the likelihood and severity of collisions and casualties.  The A614 has three loop sites within the SPECS monitored zone, which allowed an accurate comparison of vehicle speeds before and after the SPECS installation.  This provided some very useful and interesting data, which helps to explain exactly why SPECS is such an effective casualty reduction tool.

Illumination and Night Time Images

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Night time image from the A614. Note that the image is greyscale, but the vehicle’s plate is still clearly visible.

Changes in Driver Behaviour

As a quick summary, SPECS works because it changes the way people think and drive.  Through a greater awareness of the speed limit, and the fear that they may receive a fine/points, the vast majority of drivers keep their speed to very near the posted speed limit. This effect is shown on the two charts below, which both come from loop data, covering periods before and after the SPECS cameras were installed.

The charts below show vehicle speeds seen at two times; in January 2012, which was shortly before the SPECS cameras were installed and in January 2013, exactly one year later and finally, several months after installation was completed.  Data is shown for three periods:

  • 24hr (all vehicles over a 24hr period)
  • Peak (all vehicles in the most busy hour)
  • Night (only vehicles seen between 22:00 and 04:00)
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The ‘pre-installation’ chart (left) and ‘post-installation’ chart (right)

The vertical red line shows the speed limit – data to the right relates to speeding vehicles.

The ‘pre-installation’ chart shows a significant difference between the speeds seen at night and speeds during the day.  This is largely because there is very little traffic at night, so drivers tend to speed more.

The ‘post-installation’ chart clearly demonstrates how speeds have become much more uniform, or harmonised.  The night profile is virtually the same as the day profile, demonstrating that regardless of traffic volumes, vehicles are travelling at just below the posted speed limit.

Speed Variability (SD – standard deviation of vehicle speed)

Probably the most significant reason behind the effectiveness of SPECS cameras is the impact it has on speed variability, or more accurately, the reduction in the standard deviation of vehicle speed.  Before the cameras were installed, the SD rose above 10mph during the night, showing there was a very large speed differential between the fastest and slowest vehicles using the road, at the same time.  Post installation, the SD remains between 4 and 6mph.  High variability is more likely to result in collisions, which obviously has an impact on casualties but also traffic congestion.

Casualty Reductions

The primary purpose of a permanent SPECS installation is usually casualty reduction.  A study of previous installations shows that without exception, the casualty rates always drop significantly.  The formal measure of this is the Killed or Seriously Injured (KSI) figure.  It is still early days to review this fully for the A614, as the post installation data only covers 16 months, compared to five years of pre installation data.  However, before installation, on average 1.8 fatalities occurred per year.  Post installation, no fatalities have occurred and the KSI figure has dropped by 53.1 per cent.

Wider Benefits

SPECS average speed cameras have now been operated throughout the UK on every available speed limit.  Whilst the primary purpose of a SPECS installation is usually to reduce casualties and their associated impact, through experience from 300+ projects, Vysionics has also identified further benefits:

  • Smoother traffic flows.  Because speed variability is reduced, with traffic travelling at a common or harmonised speed, traffic flows tend to be better.  This results in reduced congestion and a more reliable journey time.  The reasons behind this are similar to Managed Motorways, where variable speed limits are used to maximise the capacity of a motorway.  With a uniform speed, more vehicles can fit onto the road and a conveyor belt type flow is more consistent.
  • Greener environment.  Travelling at a sensible, steady speed burns less fuel and results in lower emissions.  In addition, this means that engine and road noise are reduced, along with less wear on the road surface.  Air quality and emissions are an increasingly important issue for the government, so this benefit will become increasingly important.
  • Fairer & more acceptable.  The travelling public accept that average speed enforcement is a fairer enforcement solution, because drivers aren’t caught ‘unawares’ through a momentary lack of judgement.  In addition, because journey reliability improves, many drivers actually welcome the use of our technology because their drive to work will become more predictable.

Sonya Hurt is the Casualty Reduction Manager for Nottinghamshire County Council.  Of the benefits of the SPECS approach, she said: “The SPECS installations are proving year on year to be a known and effective method of reducing casualties both countywide and nationwide.  Where these cameras have been used elsewhere in the county, there has been an 80 per cent reduction in the number of people killed or seriously injured”.

FYI

Geoff Collins is Sales & Marketing Director at Vysionics ITS Ltd
Email: geoff.collins@vysionics.com
Web: www.vysionics.com

Thinking Highways
By Geoff Collins June 18, 2014 16:37