What We Are Learning » Are people safer walking and cycling?

Vehicle volumes and speed

Aim

In this research, we wanted to find out what the effect of the street changes were on the number and speed of motor vehicles travelling in Māngere. The street changes aimed to make it easier and safer to travel in Māngere, especially by walking and cycling.

 

Method

Different streets in Māngere were treated differently. The streets with the most traffic were called arterial streets, and streets with medium amounts of traffic were called collector streets. Both these types of streets got new or improved facilities for walking and cycling, such as crossings and bike lanes. The streets with the least traffic, which were mostly residential, were called local streets. These streets had changes to slow traffic speeds and discourage through traffic.

We used tubes laid on the road to measure the speed and number of vehicles. Councils often measure traffic in this way.

We did these tube measurements in two neighbourhoods. Māngere Central was the ‘intervention area’, where the street changes were made. Māngere East was the ‘control area’, where our project made no changes. We did the tube measurements before the street changes, in 2014, and also after the street changes, in 2017.

Once we had the measurements, we looked to see if they had changed between 2014 and 2017 in each area. We also checked whether the change in the intervention area was different from the change in the control area – this was how we worked out the effect of the street changes. 

Findings

Our results showed that in the control area, the number of motor vehicles had stayed the same on the arterial streets, but had gone up by 13-15% on the collector and local streets. But in the intervention area, the number of motor vehicles on the local streets had gone down by 11%, with small increases in traffic on arterial and collector roads.

Change in traffic volumes on local streets in control area and intervention area:

%

Control Area

%

Intervention Area

The speed of motor vehicles didn’t change in the control area, but speeds reduced in the intervention area. The biggest reductions in speed were in the local streets in the intervention area, where the average traffic speed reduced by just over 9 km/h, from 45 km/h to 35 km/h.

Average speeds on local streets before and after the changes:

before

After

This shows that the street changes reduced the number and speed of motor vehicles, compared to what would have happened without. These effects were strongest on the local (smallest) streets. The graph below shows how the speeds on local streets have reduced in the intervention area after the street changes were made. Please note that the lines on the graph have been smoothed.