The International Transport Forum recommends dropping speed limits:
Speed has a direct influence on crash occurrence and severity. With higher driving speeds, the number of crashes and the crash severity increase disproportionally. With lower speeds the number of crashes and the crash severity decrease. This relationship has been captured in various models, most notably Nilsson’s “Power Model”. This shows that a 1% increase in average speed results in approximately a 2% increase in injury crash frequency, a 3% increase in severe crash frequency, and a 4% increase in fatal crash frequency.
Thus, reducing speed by a few km/h can greatly reduce the risks of and severity of crashes. Lower driving speeds also benefit quality of life, especially in urban areas as the reduction of speed mitigates air pollution, greenhouse gas emissions, fuel consumption and noise.
All the cases indicated a strong relationship between speed and the number of crashes, i.e , an increase in mean speed was accompanied by an increase in the number of crashes and/or injured road users. Conversely, a decrease in mean speed was associated with a decrease in the number of crashes and injured road users. In no cases was an increase in mean speed accompanied by a decrease in the number of crashes or casualties. The pattern of the relationship is consistent across cases, although the size of the effect differs substantially between them. These differences are explained partially by varying definitions for injury crashes between countries and the small overall numbers of fatal crashes for some of the countries studied. . .
Based on that the ITF recommends dropping speed limits:
To reduce road trauma, governments need to take actions that will reduce the speed on roads as well as speed differences between vehicles sharing the same road. For individuals, the risks of a severe crash might seem small, but from a societal point of view there are substantial safety gains from reducing mean speeds on roads.
Set speed limits according to Safe System principles
The design of the road system and the speed limits set for it must consider the forces the human body can tolerate and survive. Working towards a Safe System, reasonable speed limits are 30 km/h in built up areas where there is a mix of vulnerable road users and motor vehicle traffic. In other areas with intersections and high risk of side collisions 50 km/h is appropriate. On rural roads without a median barrier to reduce the risk of head-on collisions, a speed limit of 70 km/h is appropriate. In urban areas, speeds above 50 km/h are not acceptable, with the exception of limited access arterial roads with no interaction with non-motorised traffic. Where motorised vehicles and vulnerable road users share the same space, such as in residential areas, 30 km/h is the recommended maximum.
There are very few New Zealand roads with median barriers and Dog & Lemon Guide editor, Clive Matthew-Wilson said the reduction to 70 kph would be unworkable.
A proposal to lower the open road speed limit to 70kp/h on stretches without median barriers is “ridiculous and unworkable’, says the car review websitedogandlemon.com. . .
“This is a knee-jerk reaction to a rising road toll and doesn’t really address the major issues. Think about it: only a tiny percentage of New Zealand roads have median barriers, even on state highways. Imposing a 70kp/h slow speed limit on long, straight roads would be met with open rebellion.”
It’s tempting now to exceed 100 kph on long, straight roads with few if any other vehicles. To lower the speed limit by 30 kph would be an invitation for drivers to rebel.
Matthew-Wilson cautiously supports the lowering of the speed limit on the most dangerous roads, but says 70kp/h, is probably too slow.
“New Zealand’s rural roads are often narrow, winding and poorly designed. On the most dangerous roads, where there are no safety measures in place, it makes sense to reduce the speed limit to 80kp/h.”
However, Matthew-Wilson says lowering the speed will have only a limited effect.
“About 80% of the road toll occurs below, not above, the speed limit. Of the 20% of accidents that occur above the speed limit, most are caused by either yobbos, impaired drivers or outlaw motorcyclists. All these groups tend to ignore speed limits anyway.”
Matthew-Wilson points out that rural drivers on secondary roads also tend to set their own speed limits.
“Lowering the speed limit may slow down tourists in a camper van, but will have little effect on the driving of most locals, who will simply ignore the new speed limits.”
“The government needs to get over the idea that average drivers and average speeds are the problem. The vast majority of accidents are caused by a tiny group of road users. Arbitrarily lowering the speed limit is unlikely to have any effect whatsoever on this high risk group.”
“If the speed limit is lowered on the worst roads, as an interim measure before median barriers are installed, I support it. If this proposal is simply an excuse to impose unrealistic speed limits across the country, I oppose it.
As things stand, I believe this proposal will cause as many problems as it solves, without having much effect on the road toll.”
There is no doubt that the higher the speed the bigger the mess will be if something goes wrong. Slower is safer but it isn’t always practical.
I live on a rural road. Most of it doesn’t even have a white line in the middle of it.
The road is several kilometres long and there are stretches with good visibility where it is safe to travel at 100 kph.
There are other stretches where a series of dips and bends make it safer to slow down and there are several kilometres of gravel where reducing speed is sensible.
The road doesn’t have much traffic on it. More often than not I don’t meet any other vehicles on it.
However, when I do it might be a tractor or stock truck which require those travelling in the opposite direction to keep well to the left and be prepared to slow down.
Locals know to take care and anyone who isn’t a local should do what we all should when we’re unfamiliar with a road – drive to the conditions which in this case means slowing down in several places.
Erecting more median barriers, targetting the yobbos, impaired drivers or outlaw motorcyclists Matthew-Wilson identifies as being the problem group and trusting other drivers to slow down when conditions require it would be far more effective than dropping the speed limit to an unworkable level.