The news has come through that the proposed 20 mph speed limit zone in South Edinburgh has been given the go ahead, which is good news. However, it is rather disappointing that the most dangerous roads inwith the area covered by the zone are being left at the higher 30 mph speed limit. As I have said elsewhere, it has been known for well over 20 years that, as traffic speed increases, so does the risk to pedestrians:

  • Hit by a car at 20 mph, 3% of pedestrians will be killed – 97% will survive
  • Hit by a car at 30 mph, 20% of pedestrians will be killed – 80% will survive
  • Hit by a car at 35 mph, 50% of pedestrians will be killed – 50% will survive
  • Hit by a car at 40 mph, 90% of pedestrians will be killed – 10% will survive
  • Hit by a car at 50 mph, >99% of pedestrians will be killed – < 1% will survive

Many drivers don’t think about the fact that at 30 mph, a vehicle travels 44ft (roughly three car lengths) every second and at 20mph a vehicle travels 29.3ft (roughly two car lengths). The average reaction time of drivers is between 1 and 1.5 seconds, it takes time to stop, drivers have to think ahead rather than just trying to react to the situation. Lowering the speed limit allows driver more time to thing and so reduces the frequency of accidents collisions.

It is also well known that the majority of drivers think that it is OK to exceed any given speed limit by 5-10 mph. As you can see from the bullet points above, this greatly increases the risk to pedestrians. However, there are some people and organisations who don’t seem to care about this, rather worryingly these include the Lothian and Borders Police, and Lothian Buses. It is widely felt that the grounds for objection were rather thin.

The Police claim they would need extra resources to enforce the lower limit if the major routes were included, and yet these are the routes which are currently in need of the greatest enforcement. If the limits on these roads were to have regular speed traps, the accident crash rates could be significantly reduced. This would in turn save the police money, as they would use fewer resources dealing with the aftermath of these crashes. Lothian Buses claim that the speed reduction on main routes would delay services and therefore require them to provide additional buses at extra cost. However, there is no evidence from other cities which have introduced 20 mph speed limits to support this. The evidence is that lower speed limits tend to smooth traffic flows and reduce the effect of congestion on bus services.

There were even objections on environmental grounds, with the Council Air Quality Monitoring Unit having concerns about the introduction of the 20mph speed limit on the busier bus corridors, due to higher gear ratios at lower running speeds resulting in greater tailpipe emissions. They claim that this is true for all vehicles, with slower buses and HGVs likely to contribute more to air quality issues in the city. Again, the evidence for this appears rather thin, this could easily be dealt with by encouraging drivers to use (appropriate) lower gears. In fact, in previous trials in cities like London and Portsmounth the introduction of 20 mph zones resulted in improved air quality. So this is really more of an excuse for not grasping the nettle and actually reducing motorised traffic through the city. The Council has a history of doing this and there have been issues with its air quality monitoring in the past.

These objections fly in the face of wide spread support from a large number of people living inwith the zone and the community councils which represent them, who had actively lobbied for the number of roads covered by the 20 mph speed limit to be increased. While the introduction of the zone is to be welcomed, it is in many ways an opportunity missed. As Councillor Steve Burgess, put it: “I was disappointed with the decision. We missed the opportunity to do something quite bold that maybe puts pedestrians and cyclists on a safer footing with vehicles in the area. It would have been good to do the whole scheme and include those roads in the pilot at the same time. I don’t think the claims by Lothian Buses and the police hold much water. It’s a missed opportunity, especially considering the community councils were supportive.”

The full report from the meeting of the Council’s Transport, Infrastructure and Environment Committee can be downloaded here