Fairfield Bridge – Lane width limit

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Germany’s experience of moving from a 50km/h to a 30 km/h urban speed limit showed – ‘frequency of accidents was unchanged, but severity was reduced’ – While this is not the focus of this post, it is a key point to consider.

The Fairfield Bridge is a real-world example of ‘A single lane road in each direction could carry between 18,000 and 20,000 vpd’ Traffic count on Fairfield Bridge over the years get close to 20,000 then drop back down.

Adding a new car lane upstream on Whitiora Bridge in 2006 was an absolute fail for people who walk or bike and it had almost no effect in reducing traffic counts on Fairfield Bridge, What is does show is the lack of effect of changing road lanes and widths on traffic counts on Fairfield Bridge. The in 2013 Pukete Bridge had 2 lanes added, again removing the on road cycle lane, forcing fast cyclists to either enter the motor vehicle lane or to mix with people walking. Again, there was almost no change in traffic counts on Fairfield Bridge. These attempts show how unsettling of adding car lanes can be, it increases car use, makes life more dangerous for cyclists and pedestrians, and has very little effect on reducing congestion.

The ideal lane width is stated as 3.5m, with 1.8m clearance to fixed obstacles close to the road. When these measurements are reduced, traffic flow is reduced. At 3.0m with no obstacle-free zones, the number of cars is said to be 58% less than with an ideal lane width. Based on the said 58% the Pukete and Whitora Bridges, with ideal lane widths and obstacle-free zones (which are used by cyclists) could move 34,000 vpd. Whitora Bridge would be okay as a 2 lane road with cycle lanes. Another important measure is ‘Traffic delays on urban roads are principally determined by junctions, not by midblock free flow speeds’.

For Fairfield Bridge the junctions at each end have been modified a number of times over the years, with the same outcome for people driving cars and limited improvements for walking and biking. The time maybe right to try a safer speed limit, so traffic moves at a more even pace; it is safer for people on bikes to mix with motor vehicle traffic; and there is a reduced to risk of harm to pedestrians crossing the road to get to the bridge foot paths or to spend money at the local shops. For people driving cars, based in Germany’s experience of moving from a 50km/h to a 30 km/h urban speed limit showed: ‘Volume were unchanged’ – ’Frequency of accidents was unchanged, but severity was reduced’ – ‘Air pollution was reduced’ – ‘Noise was reduced’ – ‘Fuel use increased or decreased depending on location’

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