Ask Phoebe: Costly lights at times run rings round rival options

Can you let us know why, using the new shopping area at Massey North (Westgate) as an example, does Auckland Transport seem to have a fixation on installing expensive traffic lights when they had a perfect opportunity to install the safer option, with better traffic flow control, of roundabouts? Is someone getting a backhander, or perhaps they have shares in the traffic light industry, or are they just unaware of the benefits of roundabouts and to hell with the expense? Ross Ferguson, Auckland.

Mark Hannan, Auckland Transport media relations manager, supplied the following: Auckland Transport doesn't have a set policy regarding the use of traffic signals versus roundabouts. When deciding on the type of control to be used at a given intersection we look at:

• The traffic volumes (or a forecast of traffic volumes).

• The types of user (ie, how many pedestrians or cyclists are we expecting to cross the intersection, is it next to a primary school or in a town centre, etc?).

• Whether we need to assign a higher level of priority to certain movements or a certain class of user.

Roundabouts and traffic signals have their own sets of pros and cons.

Roundabouts are great because they are cheaper to run, they are usually more efficient at quieter times of the day and there are generally fewer serious crashes at roundabouts when compared to other types of intersections. On the downside, it can be difficult to provide a safe environment for pedestrians or cyclists (particularly at multi-lane roundabouts). At busy times a roundabout may not provide as much capacity as a traffic signal-controlled intersection, and traffic using roundabouts can experience significant delays where approaches carry differing volumes of traffic.

Signals are often selected (a) to incorporate protected pedestrian crossings, (b) to assign priority during busy periods to main road movements (important in heavily congested areas), and (c) in some cases, you can accommodate higher traffic volumes in a smaller footprint (ie, minimising land purchases).

With regard to the Westgate area north of Fred Taylor Drive, the town planning, including decisions on the form of the intersections, was completed before Auckland Transport was formed in late 2010.

This area was designed as a town centre and employment hub with some integrated parks and open spaces. This type of environment encourages a lot of people to walk between the various activities. One of the main drivers for using traffic signals at a lot of these intersections was therefore to make it as safe and convenient as possible for pedestrians.

• Further to last Tuesday's column, Gary Darlington has written in to say that the new traffic hump in New Windsor Rd is part of the new cycleway from Maioro St to New Lynn. The present bus shelter has been shifted and the hump will allow cyclists and pedestrians to cross New Windsor Rd with more safety.

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Do you have a question for Phoebe? It can be about transport or any Auckland issue. Email askphoebe@nzherald.co.nz