Shamubeel Eaqub is an economist at Sense Partners, an economic consultancy.
There is a proposal to set a 30km/h speed limit in Auckland city centre. The debate is heated and polarising, but the evidence is more complex and nuanced than either side of the debate claim. Importantly, travel in the city centre is already much slower than the proposed speed limit – so there will be only a minor change in practice.
My research of the international evidence suggests speed is a low cost, effective and easy way to calm traffic. A lower speed limit is a signal to make our city safer for everyone, at minimal inconvenience to individual drivers.
From a personal perspective, my journeys into the city are usually slow. I never get to the speed limit. Most of my activity in the city during the week is on foot, meeting people all over town. In the weekend, when I take the family to town, its with a pram and a toddler on foot. I often wish the city was more pedestrian friendly. If the lower speed limits mean the traffic is calmer and more people can get about the city safely and easily, it is worth doing.
Roads are for everyone
Roads are used by everyone. The debate often pitches car users against others. But, if we are fair, we should consider everyone who uses the road. In the city centre, walking is the dominant way of getting around.
Crashes and collisions happen despite safer cars, roads and regulations. In urban areas, people walking and cycling are at particular risk. A key factor in reducing injury and risk of death is speed.
There are lots of people in a relatively small physical area in Auckland’s city centre. There are lots of people living in the city (around 55,000), many people come to work (around 120,000), study (around 100,000 students), and visit (around 20,000). At the same time, traffic volumes in the city have been broadly flat over the last decade.
We should expect to see even more people living, working and playing in the Auckland city centre in the future, but there is not much room for more cars. So, our approach to roads must place a greater focus on safety and-place making for the changing nature of Auckland city centre.
Lower speeds reduce injury and death
There is convincing evidence from around the world that lower speeds reduce the risk of collisions and reduce the severity of injury and fatality when crashes happen. The increase in individual travel times is modest (typically measured in seconds rather than minutes).
More and more cities are reducing speed limits in highly pedestrianised areas. Sydney is expanding its 40km/h speed limit, Sweden has a default 30km/h speed limit in residential areas in Stockholm and more European cities are adopting lower limits in urban areas. Unless the speed limits are credible, supported by other traffic calming measure, many drivers will drive faster when possible.
Historically, our road design and speed rules have put the mobility of drivers in opposition to other users, such as people walking. Taken as a whole, we need to improve the entire system: safe roads and roadsides, safe speeds, safe vehicles, and safe road use.
Speed limits vs actual speed limits
Speed limits are not speeds travelled. In most urban areas the average speed of travel is well below the speed limit. Auckland is no different. Measured across several key roads in the city centre, the average speed of travel across different parts of the day are typically under 15kph, even on main arterials like Hobson and Nelson Streets. Our roads are at capacity and we can’t drive fast in the city centre, especially during peak times. The new proposed speed limit is unlikely to affect many trips.
Speed limits don’t always equal efficiency
Reductions in speed limits may have some benefits on roads at capacity, according to literature. In some cases, a lower speed limit can improve traffic flow (if accompanied by traffic light phasing and if drivers don’t stop-start and clump), improve fuel efficiency, reduce pollution and noise. But the impact is marginal. This requires additional investments to changing the speed limit.
When speed limits are too low during quiet times, drivers are likely to speed. As the speed limit does not seem credible. In some busy streets a 30km/h speed limit may see speeding during off-peak times, and add to journey times.
The benefits and costs fall differently
As a general rule, lowering speed limits increase individual travel times very marginally, but are effective in reducing injuries and deaths. In the case of Auckland's city centre, there is unlikely to be much of an impact, where speeds are already very low.
There is some debate about how the slower journey should be considered. At an individual driver level, or accumulated to all drivers. From an economic perspective, the cumulative effect matters. But from a political perspective, the individual impact seems more important for a very individualistic activity like driving.
The main benefit in Auckland will be to moderate speed expectations commensurate with the capacity of our roads. Done right, it will have little negative effect, but may be made positive by creating better flow of traffic.
Speed limits are one part of the puzzle
Speed limits are only one part of traffic calming measures. Strategies include slowing down traffic (for example, speed humps, mini-roundabouts, reduced speed limit zones), visual changes (road surface treatment, changes to road lighting), redistributing traffic (blocking roads, creating one-way streets), and/or changes to road environments (such as trees). We should be using all measures to ensure the city centre environment is calm for all road users and speed limits are credible in the context of the street.
Auckland city centre is increasingly about people. A lower speed limit will send a strong signal that the city centre is for everyone. But the international experience suggests that there is some uncertainty on the exact speed limit best suited for urban areas. In Sweden for example, they use 30kph and 40kph depending on the urban context to find the right balance between travel-time loss and safety gains.
There seems little harm in introducing a new 30kph speed limit. But the new limit should be studied closely to monitor travel-time loss and safety gains. Authorities should be willing to change the speed limit in the future if the evidence speaks loudly.
Only with good evidence and transparency will the polarising and shrill debate on the speed limit be settled.
 Placemaking is a multi-faceted approach to the planning, design and management of public spaces that promotes people's health, happiness, and well-being.
 Jeffery Archer, Nicola Fotheringham, Mark Symmons and Bruce Corben. “The Impact of Lowered Speed Limits in Urban Areas”. Monash University Accident Research Centre 2008.1
 Bunn F, Collier T, Frost C, Ker K, Steinbach R, Roberts I, Wentz R. “Area-wide traffic calming for preventing traffic related injuries”. Cochrane Database of Systematic Reviews 2003, Issue 1. Art. No.: CD003110.