Roundabout Design Safety Issues In Halswell Junction Road, Christchurch

A newspaper report in Christchurch highlights possible design issues in Halswell Junction Road. The video clip supplied shows that the incident in question took place at the roundabout at the intersection of Halswell Junction Road and Alvaston Drive / Hamill Drive. This was originally a T intersection as seen in this 2011 aerial view.

Halswell Junction Road / Alvaston Drive intersection as seen in February 2011,

Google Earth coverage shows that in 2012, a subdivision was developed in the lower (greenfields) area of this view. As the above shows, a new street, Hamill Road, was built as part of the subdivision development, and to handle the flow of traffic between this subdivision and Halswell Junction Road, a roundabout was installed at what has now become a four way intersection. The map below shows what the intersection has looked like since late 2012 when the road layout was changed.

Halswell Junction Road / Alvaston Drive / Hamill Road intersection as it appears today.

There is one thing that is very striking about this layout and that is the asymmetrical nature of the intersection, with the centre of the roundabout being offset from the alignment of Halswell Junction Road. We can see that the south side of the roundabout (for traffic heading east to west on Halswell Junction Road) has noticeably sharper curvature than the north side (west to east) or the east or west sides. This curvature, in fact, is most unusual in roundabouts on arterial roads like Halswell Junction Road , which in that locality has a signposted speed limit of 50 km/h. It is much more common to see that degree of curvature on roundabouts in residential streets where average speeds are likely to be lower.

For this reason it seems entirely reasonable that we must question the design of the roundabout as created by the Council’s engineers. There is no real question that a roundabout would be considered appropriate for this type of intersection, however there is a real challenge in why the Council allowed on Halswell Junction Road, an arterial route with higher speeds, a sharply curved road around a roundabout to the extent that it is highly likely these situations are occurring because of lack of familiarity with these sharp curves on the part of some drivers, in other words excessive speed for the nature of this intersection where straight through traffic is required to traverse curves that are much sharper than those typically seen in roundabouts on other roads like Halswell Junction Road. This must then come down to the design being an attempt to fit a roundabout into an existing road layout at the cheapest possible cost. The asymmetric design with the roundabout being off-centre has forced these sharp curves into the road layout for vehicles travelling from east to west on Halswell Junction Road, and it is in fact the case that that is the direction that traffic is following in the instance shown in the video clip included in the online news report.

This one will be watched with interest as this clearly shoddy and substandard road design has resulted in one local landowner having multiple vehicle crashes on their property from drivers losing control on the roundabout heading in the east to west direction. No doubt they will face a major battle to get the Council to take responsibility for addressing the intersection design issue.

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