On 31 May 2019 the BBC reported that “Holyrood’s rural economy committee has refused to back a Bill seeking to make 20mph the standard speed limit on residential streets in Scotland”. Edward Mountain a conservative MSP for the Highlands and Islands and Convener of the Rural Economy and Connectivity Committee explained that “After considering the evidence presented in the Bill introduced by Mark Ruskell a Scottish Green Party MSP for Mid Scotland and Fife, the majority of the committee thought it was not appropriate. The “one size fits all” was not suitable and local authorities should have the flexibility to introduce 20mph speed limits as they think appropriate for their areas.
Surely “one size fits all” is not true at the moment and does not need to be true if this Bill becomes law. As far as I am aware all this Bill is suggesting is to reduce the 30mph default speed limit down to 20mph on restricted roads. These restricted roads are residential streets and minor roads in urban areas. At present local authorities can and do have flexibility to introduce special speed limits such as 20mph near schools or in known accident blackspots.
These 20mph zones outside schools that are clearly marked with flashing signs are, I agree acceptable. Most people travelling past local schools are aware of these and the clear warnings help motorists to comply with the speed limits. I also accept that sections of roads that have been identified as accident black spots may need to have a reduced speed limit. Providing these are clearly marked and alternative methods have been considered, then this is also acceptable. However, more and more residential roads are being designated as 20mph zones, often requested by residents in “the interests of safety”. However, with the existing default speed of 30mph in residential areas being reduced there is the risk of confusion when law-abiding motorists don’t realise, they have entered a 20mph zone.
The Institute of Advanced Motorists (IAM) in 2016 made recommendations that 20mph speed limit zones must be self-enforcing through signposting that makes sense or traffic calming features. They also stated that “given the low number of injuries on residential roads limited police enforcement resources must be prioritised elsewhere”.
This recommendation has been reinforced by the Transport Scotland – Good Practice Guide on 20mph speed restrictions version 2 published in June 2016. This states under the “Enforcement” section that the police will not routinely enforce the 20mph speed limit and a range of other measures should be employed including marketing, behaviour change initiatives, vehicle activated signs and traffic management and other traffic calming measures. The four main techniques used in traffic calming are recommended in the Royal Society for the Prevention of Accidents (RoSPA) – Road Safety Factsheet published in November 2017. These are vertical deflections, horizontal deflections, road narrowing and central islands.
These 20mph zones requirements for traffic calming measures incur additional cost to local authorities to retrofit to existing streets and an ongoing maintenance cost. Many motorists also tend to increase speed when approaching these traffic calming features to avoid a possible delay.
The required traffic calming identified in the Transport Scotland guidance and RoSPA factsheet will inevitably cause vehicles to accelerate, decelerate and brake at these traffic calming measures. During busy times of the day, when children are likely to be on the footways, vehicles may have to wait for oncoming vehicles at the road narrowing sections, with their engines running.
Research in Germany has shown that the greater the speed of vehicles in built-up areas, the higher is the incidence of acceleration, deceleration, and braking, all of which increase air pollution. Many of the streets in both villages and towns consist of older closely built houses in narrow roads, all of which can cause accumulation of atmospheric pollutants.
Depending on the atmospheric conditions pollutants including carbon dioxide (CO2), carbon monoxide (CO), nitric oxide (NO), sulfur dioxide (SO2) and nitrogen dioxide (NO2) could build up between the buildings. Small carbon soot particles can also be released from vehicle exhausts often referred to as particulate matter and designated as PM10 (less than or equal to 10 micron) or PM2.5 (less than or equal to 2.5 micron). Nitrogen dioxide, nitric oxide and carbon monoxide can react due to sunlight to produce ground level ozone (O3). All of these air pollutants can be a health risk, causing respiratory conditions or other forms of poisoning, particularly to the elderly or young children.
A report by the Transport and Environmental Analysis Group published in 2013 indicated that reducing the speed limit from 30mph to 20mph would have a small but positive impact on pollution. I could not find any more recent studies based on vehicles complying with the EURO 6 emission standards.
It seems to me, although I am not a politician, that to avoid confusion, cost and reduce pollution risk, rather than have local authorities introduce 20mph zones on an ad hock basis across Scotland, as the Rural Economy and Connectivity Committee appears to be proposing, that reducing the 30mph speed limit universally down to 20mph would be a sensible solution. Once all motorists accept that the default speed limit in residential and minor roads is 20mph there will no longer be a need for traffic calming measures and after the initial cost of new 20mph signs for local authorities the ongoing maintenance costs will be significantly less.