Average speed across different parts of the day are typically under 15km/h, even on main arterials such as Hobson St. File photo / Doug Sherring
Average speed across different parts of the day are typically under 15km/h, even on main arterials such as Hobson St. File photo / Doug Sherring
COMMENT:
The debate around a proposal to set a 30km/h speed limit in Auckland city centre is heated and polarising but the evidence is more complex and nuanced than either side claims.
Importantly, travel in the city centre is already much slower than the proposed speed limit – so, inpractice, there will be only minor change. My research of the international evidence suggests speed is a low cost, effective and easy way to calm traffic.
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 living in the central city (around 55,000), many people come to work (around 120,000), study (around 100,000 students), and visit (around 20,000). Traffic volumes in the city have been broadly flat over the past decade.
We should expect to see even more people in the Auckland city centre in the future, but there is not much room for more cars. So, our approach must place greater focus on safety and place-making for the changing nature of Auckland city centre.
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 traffic flow.
There is convincing evidence 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). In the case of Auckland city centre there is unlikely to be much of an impact, where speeds are already very low.
More cities are reducing speed limits in highly pedestrianised areas. Sydney is expanding its 40km/h speed limit and Sweden has a default 30km/h speed limit in residential areas of Stockholm.
However, many drivers will drive faster when possible, unless the speed limits are credible and supported by other traffic calming measures,
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 are not speeds travelled. In most urban areas, the average speed of travel is well below the speed limit. Measured across several key roads in the Auckland city centre, the average speed across different parts of the day are typically under 15km/h, even on main arterials such as 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.
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 limit does not seem credible. In some busy streets, a 30km/h speed limit may lead to speeding during off-peak times, and add to journey times.
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 such as 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 traffic flow.
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.
There is some uncertainty on the exact speed limit best suited for urban areas. In Sweden for example, it is 30km/h and 40km/h, 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 30km/h 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.
• Shamubeel Eaqub is an economist at Sense Partners, an economic consultancy
