We have just submitted our response to the Rural and Economic Connectivity Committee of the Scottish Parliament consultation regarding the "Restricted Roads (20mph speed limit) (Scotland) Bill". This bill will set a national 20mph limit (instead of 30mph) for most restricted roads with the ability of local traffic authorities to make exceptions which will retain a 30mph limit. It provides for national consistency and local flexibility.
"We applaud the Scottish Government in progressing this bill to its current stage. It provides a huge opportunity to align Scotland to what is becoming best practice across the world and especially in more socially aware countries. It aligns Scotland with such countries as Denmark, Norway, Netherlands, Sweden, Switzerland, France, Belgium, Austria, Germany and Japan where 30kmh is the accepted norm in communities whether urban or rural.
It will move Scotland away from the English model of inconsistent local setting of speed limits on built-up roads based on council priorities, values and empathy with communities. It will instead provide for a common national value of how roads are shared and do what national governments do best by setting those standards, facilitating implementation yet still allowing the flexibility for exceptions to be determined locally."
Our full response follows.
RURAL ECONOMY AND CONNECTIVITY COMMITTEE
RESTRICTED ROADS (20 MPH SPEED LIMIT) (SCOTLAND) BILL
SUBMISSION FROM Rod King MBE on behalf of 20’s Plenty for Us
- Is reducing the speed limit to 20mph the best way of achieving the aims of the
Aim 1. Enhancement of road safety.
In answering this question, we will cite several reports from global organisations. In general, these will refer to speeds and limits in kmh. Those most quoted are 30kmh (18.5mph, equivalent to 20mph) and 50kmh (32mph, equivalent to 30mph). 1 kmh is equal to approximately 0.6mph.
As part of the 4th UN Global Road Safety Week, May 8th-14th 2017, the World Health Organisation (WHO) focussed on vehicle speed as the major factor in most collisions. Its document on Speed Management says:
“A safe speed on roads with possible conflicts between cars and pedestrians, cyclists or other vulnerable road users is 30 km/h (see Table 2). To achieve these safe speeds, local authorities should have the legislative power to reduce limits as needed to better protect all who use the roads. In addition, drivers should be informed of limits through sign-posting the legal speed limit on roads and rigorously enforcing the law.”
In its document “Manifesto #4RoadSafety” the Global Network for Road Safety Legislators set out its recommendations and legislative priorities. Within this it notes:
“There is strong evidence that wherever motorised traffic mixes with vulnerable road users, such as pedestrians, cyclists and mopeds, the speed limit should be set at or under 30 km/h.”
The International Transport Forum of the OECD published a report in 2018 calling for a 30kmh speed limit in built-up areas where there is a mix of vulnerable road users and motor vehicles. The report is categorical that :
“Where motorised vehicles and vulnerable road users share the same space, such as in residential areas, 30 km/h is the recommended maximum.”
It cites 30km/h as the developing international standard referencing the Netherlands where 70% of urban roads have a 30km/h limit. Also :-
“In many countries, there is a trend into generalising the 30 km/h zones in city centres and residential areas. As mentioned above, some countries are considering setting 30 km/h as a default speed limit in urban areas, with possible higher limits on arterial roads. Most countries report undertaking regular communication campaigns to promote lower speeds and better compliance with the speed limits.”
It repeatedly recognises the benefits of 30km/h limits for reducing injuries to pedestrians and cyclists:-
“Research has indicated that the death risk is about 4-5 times higher in collisions between a car and a pedestrian/road worker on foot at 50 km/h compared to the same type of collisions at 30 km/h. Considering this, there is a strong recommendation to reduce speed in urban areas.”
The report concluded:-
“To reduce road trauma (i.e. fatalities and injuries), governments need to take actions to reduce the speed on our roads and also to reduce differences in speed. As individuals, the risks for a severe crash might seem small, but from a societal point of view, there are substantial safety gains when the mean speeds and speed differences on the roads are reduced.”
Quite small reductions in average actual speed have a larger reduction in casualties. The WHO report on speed management quotes that for every 1kmh increase in speed there is a 3% incidence of crashes and a 4-5% increase in fatal crashes. This is echoed in the Transport Scotland Good Practice Guide on 20mph Speed Restrictions which quotes a 4% to 5% reduction in crashes for each 1mph reduction in vehicle speed.
Speed itself may not be the cause of a crash but it is almost always the reason why the driver is not able to take the avoiding action that could have prevented the crash. But the survivability of vulnerable road users as pedestrians and cyclists is particularly affected by speed. In the WHO factsheet on “Road Safety – Speed” it notes:
“For example, pedestrians have been shown to have a 90% chance of survival when struck by a car travelling at 30 km/h or below, but less than 50% chance of surviving an impact at 45 km/h.”
Whilst there may be some academic debate on the exact percentages, it is acknowledged that the rise in risk to pedestrians rises significantly above 20mph and even more so for elderly pedestrians. The following are taken from 2011 research from the AAA Foundation for Traffic Safety reported by Pro Publica.
The website referenced below includes an interactive graph.
There is also a great deal of evidence from current wide area 20mph Highway Authority implementations in the UK that they have benefited road safety. These typically show casualty reductions of between 20% and 30%. These include Warrington, Brighton & Hove, Newcastle, Portsmouth, Bristol and Calderdale. All of these were “statistically significant” and covered casualties across a large area. They can be seen in the 20’s Plenty Report on Casualties.
The committee may be aware of the 20mph evaluation conducted for DfT by Atkins. Unfortunately, this chose residential Case Study Areas which it recognises were too small to have any statistical significance. The number of casualties in the areas chosen was typically less than 20 per annum, so nothing can be inferred from such results. The only area in the report to have a large enough area to be statistically significant was in the Brighton city centre which recorded a 20% reduction in casualties compared to a similar area not implementing 20mph limits (but also implementing other road safety initiatives). A full critique of the Evaluation Report has been made by 20’s Plenty. Note that the evaluation has also been criticised for its use of TomTom data for speed analysis which comprised an estimated mere 3% of traffic. The committee should therefore be careful attributing any significance to casualty figures in the Evaluation Report.
The committee may also be aware of newspaper headlines in 2018 that 20mph limits had increased fatalities in Bath. This was totally bogus and related to an obscure analysis of KSIs (Killed or Serious Injuries) in a report from Bath and North East Somerset Council that unjustifiably attributed significance to KSI changes from 0.8 to 1.0 in individual wards. This led to the Scrutiny Committee receiving the report to “take no action”. However, the report did detail that total casualties on 20mph roads in the City of Bath had reduced by 23% following implementation. A critique of the report is available.
Note that cities already advocating a national 20mph default limit include London, Birmingham, Cardiff, Edinburgh and Glasgow.
We would therefore suggest that:
- 20mph limits are a key platform to increase road safety that has widespread acceptance across the world
- Even small reductions in speed have measurable and beneficial reductions in crashes and casualties.
Aim 2. Changing driving culture and promoting compliance with speed limits
Whilst current Transport Scotland policy is broadly supportive of 20mph for residential areas and places where people shop, learn, work and play, much of the legislation and guidance is constructed around the national 30mph limit being the norm for urban and village roads and 20mph being an exception. This is further endorsed when signage regulations are based on the 1990’s situation in which a 20mph limit was a rare exception on the roads. This creates a public consensus that 30mph is the endorsed norm and slowing down to 20mph is only required in specific places.
This is the opposite of many other European countries where 30kmh (18.5mph) is the norm and “going faster” with a limit of 50kmh (32mph) is only deemed appropriate in certain roads where adequate segregated provision is made for pedestrians and cyclists.
The “establishment norm” of 30kmh is therefore key to setting a “social norm” whereby 30kmh becomes the reference point for how we share and use streets in communities.
The process around setting what is the 20mph exception in Scotland (and the UK generally) is complex administratively and hence builds in a process bias against adopting wide-area 20mph limits in a cost-effective manner. The need to go through the justification process to adopt a 20mph limit that is different from the 30mph norm also perpetuates the social norm of 30mph with a consequential effect on compliance.
Hence, if one accepts that a 20mph limit is the correct and only appropriate limit for where motor vehicles mix with unsegregated pedestrians and cyclists then it is entirely appropriate to adopt this at national rather than local level. This has the effect of both debating and adopting that social consensus in terms of national values of driver responsibilities, active travel aspirations, protection of the vulnerable, etc. It also allows a national media and engagement program to be developed in a more cost-effective way than doing so in communities locally, as well as a national consistency of enforcement to back up that developing social norm and driving culture.
Note that there is also a similar case for England, but with 153 diverse highway authorities and a government that appears to have less empathy for active travel and vulnerable road users, this is progressing slower than in the devolved nations of Scotland and Wales with 32 and 22 highways authorities respectively. Scotland and Wales also have a very strong commitment to active travel and using this commitment to develop driver behaviour change.
There is also strong evidence that the public consensus is that 20mph is the right speed limit for residential roads. Successive British Social Attitude Surveys have shown strong support. The last survey addressing this in 2015 found 68% of the public and 66% of drivers strongly agreeing or agreeing with “having speed limits of 20mph in residential streets”. Note that whilst 65 and over showed the strongest support for such 20mph limit (76%) they also showed the lowest support for speed bumps (42%).
There is good evidence that there is a strong aspiration from the public for 20mph limits for residential streets. This provides an opportunity to convert this into behaviour change which will be enhanced by adopting 20mph limits on a national rather than local basis.
A localised, postcode based, and inconsistent adoption is not conducive to developing a social norm when adjacent highway authorities have different interpretations as to what is the social norm. Some drivers in a 20mph authority will see justification for non-compliance if similar streets in an adjacent authority have 30mph limits.
With regard to actual behaviour change, there is good evidence that 20mph limits do produce beneficial reductions in speed. In practice the higher speed reductions on faster roads are diluted by the many roads included for consistency where speeds are already below 20mph. Hence a typical 1-2mph reduction in average speed across a whole 20mph road network will have variations between 0mph on slower roads to 7mph on faster roads. Whilst a 1-2mph speed reduction from a driver perspective may not seem a significant difference in terms of potential harm or crash avoidance, when looked at as a population or network wide reduction in motorised vehicle kinetic energy is significant. A reduction from just 24mph to 23mph results in an 8% reduction in kinetic energy.
Note that in authority-wide 20mph implementations in the UK many techniques have been used (apart from physical calming) to enhance behaviour change. “Physical calming” has a very local effect and encourages speeding up once the physical calming is no longer present. On the other hand, reducing speed through “behaviour change” endorses a 20mph norm throughout the road network.
With regard to compliance, we note that in para 16 of the written submission from the Scottish Parliament it references “the latest statistics from Department for Transport (DfT) show that in 2016 over 80% of cars and large vehicles exceeded 20mph”. The DfT report in question was analysing the speeds at only 8 20mph sites across the whole of the UK which were selected for being “free-flowing” and devoid of any hazards. The report further stated that these were atypical of most 20mph roads. A Freedom of Information request showed that most were not residential roads. The extrapolation from these 8 atypical roads to a generalised comment that attributes this statistic to all 20mph roads is misleading. Note that even on these “free-flowing” roads speeds were 6mph lower than on their equivalent 30mph roads.
Aim 3. Improving health outcomes and more active travel.
A default 20mph limit is not a silver bullet for active travel. However, it is accepted as a necessary foundation for active travel. Many other active travel initiatives such as segregated facilities, bike sharing, cycle training, safer junctions, modal shift, quieter streets, walkable streets and better air quality all benefit from having a low speed limit and lower speeds on the interconnecting network. Even with some segregated cycle facilities people still need to get from their start to those facilities and then to their destination.
Look at any city/place that has successfully encouraged active travel and you will find low speed limits of 20mph or 30kmh on most streets. That is why 20mph limits as the norm are called for by WHO, Royal College of Paediatrics and Child Health, Faculty of Public Health in Scotland, Glasgow Centre for Population Health, Public Health Wales, Association of Directors of Public Health, NICE and so many NGO representing cyclists, walkers, children and the elderly.
For the elderly they are particularly important. A 75-year-old that decides not to walk to the shops on a regular basis due to speed of traffic and perceived danger not only loses their independent mobility but also starts a process declining fitness through inactivity. This in turn has an impact on health and NHS costs.
A national limit makes a symbolic statement that active travel and the protection and comfort/convenience of those who choose to cycle and walk matters. This is far more effective when it reflects a “national value” rather than the view of a particular local authority.
Aim 4. Addressing inequalities in casualties from road accidents between deprived and non-deprived areas.
A child in the most deprived wards in UK is 4 times more likely to be injured as a pedestrian than in the least deprived wards. This is often a case of exposure. Children in deprived wards are more likely to have no car in their family. They have no choice other than to walk or cycle to school, or to the shops, or to their relations or friends.
The British Academy asked 9 prominent members for single interventions which would reduce health inequalities. Prof Danny Dorling, Halford Mackinder Professor of Geography at the University of Oxford, chose 20mph limits and his report was subsequently published by the British Academy. One of his arguments was that grouped cause of death, the biggest killer in Britain of children between 11–16 years old (and, in fact, anyone between the ages of 5 and 25) is road traffic crashes. That includes a vehicle hitting a pedestrian, a pedal cyclist being hit by a vehicle (most often a car, sometimes a lorry), or the death of a passenger or driver in a vehicle during a crash. For children, the risk of accidents is higher in faster traffic environments because their eyes are not developed enough yet to be able to judge speeds over 20mph.
Professor Dorling’s closing comment was :
“In many urban areas in mainland Europe, 18.6mph (30km per hour) is now normal in residential areas. It will become normal in most residential areas in Britain also. All that is in question is how many people will have to suffer before that occurs. And, of all those who suffer, proportionately it is children more than any other group – especially children growing up in poorer areas.”
It is not only children, but adults and the elderly as well. Not only is a national 20mph limit that symbolic representation of their right to share the roads as pedestrians and cyclists, but also a step change in the speed on such roads.
It also gives them greater civil law protection. There is also an English civil law precedent regarding driving above 25mph in a 20mph limit and colliding with a pedestrian. This places the driver as being 100% liable for the consequences regardless of any negligence of the pedestrian. Whilst we are not competent to advise on the transferability of the precedent in the High Court to Scotland, the case of Rehman v Brady does provide a level of civil protection for pedestrians where a vehicle is driven above 25mph in a 20mph limit.
The national limit is therefore particularly important for reducing health and casualty inequalities.
Aim 5. Contributing to a reduction in pollution from vehicle emissions.
Any discussions of emissions regarding 20mph limits are usually complemented by anecdotes and suppositions. However, the physics of vehicle movement and energy are well known. The activity that most produces emissions is not steady-state driving with little variation in speed but is acceleration and deceleration. The former requires fuel energy proportional to the terminal speed squared, whilst the latter requires the dissipation of that same energy so emitting brake and tyre emissions. A vehicle accelerating to 30mph requires 2.25 times the energy required to get to 20mph.
Unfortunately, many perceptions of emissions and speed date from measurements of air quality at various sites and then comparing them with the average speed. In such sites it is the level of congestion that tends to create the start/stop progress and hence reduces air quality whilst at the same time reducing the average speed. Air quality is not an output from average speed, but both are an output from congestion. Whilst there is correlation between average speed and air quality, there is no causation.
Older evaluations do indeed show air quality is lower where average speeds drop to 20mph where congestion is the cause of the lower speed with its stop/start vehicle behaviour. However, in situations where it is a speed limit that induces the lower speed there is no start/stop behaviour and so smoother driving results in higher air quality.
Research for City of London Corporation by Imperial College London modelled typical vehicle cycles in a 20mph and 30mph limit environment and found the biggest reduction was 8% in NOx and PM10 emissions for diesel vehicles from a 20mph limit. Whilst there was an 8% increase in NOx for petrol cars this was only a tenth of the decrease for diesel cars. Taking into account the normal mix of diesel/petrol vehicles then a 20mph limit is equal to taking nearly half of the 63% of petrol cars off the road. The report notes “It is concluded that it would be incorrect to assume a 20mph speed restriction would be detrimental to ambient local air quality, as the effects on vehicle emissions are mixed.”
20mph limits also reduce braking and tyre wear emissions. Modal shift is another factor when car drivers decide to walk, cycle or use public transport that reduces emissions.
NICE, the National Institute for Health and Care Excellence, reviews evidence on health policies. It has published guidance on Air pollution: outdoor air quality and health in June 2017 which strongly supports 20mph limits for smooth driving and speed reduction. It advises authorities to set:
“20 mph limits without physical measures to reduce speeds in urban areas where average speeds are already low (below around 24 mph) to avoid unnecessary accelerations and decelerations”
- How will the 20mph Bill affect you?
20’s Plenty for Us has local community campaigns throughout the UK including Scotland. These are people from all walks of life, all ages and include motorists, cyclists and pedestrians. Indeed, most will do all three (but not at the same time). These campaigns represent the near 70% of the population (see BSAS stats above) who say that 20mph is the right speed limit for residential roads and where people walk and cycle on roads used by motor vehicles. This bill allows the aspirations of those communities to be met in manner that combines national values on how the streets are shared with local authority flexibility in taking account of the exceptions where a 30mph limit will be retained.
It will be welcomed by our local campaigners in Scotland. It will also be welcomed by campaigns throughout the UK and beyond as they see Scotland taking a progressive, practical and pragmatic approach to reducing speeds on Scottish community roads and making them better places to be. They will see Scotland moving itself towards a more Scandinavian model of implementing lower speed limits where people are on a national basis rather than the inconsistent postcode lottery on vulnerable road user protection that exists in England.
Tourists will also benefit from lower speeds. Both because those from many countries will have 30kmh limits themselves, but also their familiarity with driving on the left may leave them exposed to higher risk as a pedestrian.
- It is proposed that a national awareness campaign is required to introduce a 20mph speed limit. Do you agree with this? And if so – what shape should any campaign take?
Engagement and awareness are key factors in gaining behaviour change. Best practice in implementing 20mph limits is seen in Bristol, Calderdale, Edinburgh, Birmingham and London Boroughs, which all include multi-media engagement. Some notable practices are:
- Develop community ownership of the benefits of driving slower.
- Universal implementation means most people gain on their home streets.
- Use of Facebook, Twitter and other social media
- Use of banners, poster on roads, especially where additional engagement is beneficial.
- Involvement of schools, particularly around modal shift for children.
- Recognition that 30mph is no longer appropriate where people mix with motor vehicles.
- Recognition that journey times are not so dependent on actual speed between congestion points or junctions and are more a function of how long stopped in stationary traffic.
In most local authority implementations, it is not practical to use mainstream press and TV media. However, taking a national approach provides the economy of scale to use these methods of engagement. This can particularly be developed around a Scottish ownership of the 20mph initiative and it making Scotland a better place to be.
- Should Police Scotland be required to take additional enforcement action, over and above that used to enforce the current 30mph limit, following the introduction of a default 20mph limit on restricted roads?
Yes. Despite a strong engagement program, there will always be drivers who will determine their own compliance levels to any speed limit by their risk of being apprehended. Unfortunately, a myth has developed that 20mph limits are not enforceable and a view that the police will not bother to enforce them.
It is therefore important to ensure that 20mph limits are respected by the motoring public. Police forces in other parts of the UK have been successful in using 20mph Speed Awareness Courses as an option instead of Fixed Penalty Notices where appropriate. These offer the driver an alternative that enables them to understand why 20mph limits are set and their benefits, as well as the ability for the course fees to contain an element of charge that goes back to the police force to fund the enforcement resources. Avon and Somerset Police have been successful in this and have been complemented by the work of Bristol City Council in support. This includes Community Speed Watch run by volunteers.
Avon and Somerset Police also publish schedules of their speed camera sites, so publicising their existence. This sends a strong message to drivers that 20mph limits are just as enforceable as 30mph or any other speed limit. West Midlands Police are taking a similar robust approach.
Enforcement of 20mph limits does not require a policeman on every corner, but the existence of some enforcement is important not only in identifying those drivers who are do not wish to comply, but also in supporting those drivers who do comply and feel that non-compliant drivers should be sanctioned.
Surveys have shown a high level of support for the enforcement of 20mph limits by drivers on the basis of fairness. In a YouGov survey Professor Alan Tapp of University of West of England found that 57% of those asked agreed that “I hope the police will enforce 20mph limits”. In addition, 74% agreed that “People will ignore 20mph limits because they don’t see themselves getting caught by police”.
Note that there may be alternatives to the Police being the sole enforcement agency for speed limits. Police forces may delegate enforcement to other bodies such as local authorities who can run their own Speed Awareness Courses. This is clarified in a 20’s Plenty Briefing Sheet – How Local Authorities Can Enforce 20mph Limits.
- What kind of timescale is needed for the 20mph speed limit to be introduced?
Most local authorities implement their authority-wide 20mph limits across 2-3 years for an average population size of 200,000. However, this includes planning for significant additional signage for repeaters.
Implementing on a national scale provides many opportunities to make this simpler. However, there could be benefit from planning and possible changes in signage practice which could streamline the process. We see the process very much one of national government planning and facilitating the process whilst local government implements the change.
Some considerations are:-
- Are repeater signs on roads without a national speed limit really necessary? They are not used in most other countries which solely rely on boundary signs?
- Could the use of peelable decals on signs be useful in converting 30mph signs to 20mph, or for erecting a 20mph sign and peeling off a 30mph decal when the actual limit changes?
- Could highway authorities be allowed to have different implementation schedules but with a final fixed date whereby all 20mph signage and limits would require to be set?
- Could the use of experimental traffic orders enable highway authorities to set their own timescales for implementation yet cost effectively and easily align themselves with the national limit change?
The above are suggested as ideas and are not exhaustive. However, a creative use of changing signage and implementation schedules could make the whole process easier for highway authorities to resource. In all cases we believe that signage should always be in alignment with the actual speed limit applying to a road at any time.
- Do you have any comments on the impact that the Bill might have in relation to the following:
➢ human rights or equalities for any particular group of people?
We believe that this will provide benefits for the young, the elderly, the disabled. Most carers taking children to school tend to be mothers.
Hence this initiative does have beneficial outcomes for those with protected characteristics of age, disability and gender.
➢ sustainable development?
Many communities and authorities recognise the benefits of modal shift on sustainability. Hence this initiative will provide a benefit for sustainable development.
➢ island, rural or remote communities?
When looking at current authority-wide 20mph implementations we see that urban conurbations have been the early adopters. However, there are some notable exceptions shire counties such as Lancashire, Fife and Clackmannanshire. It is not that rural or remote communities cannot benefit from 20mph limits. Indeed, children need just as much protection walking to school in rural environment as in urban environment.
The benefit of a national setting of a 20mph limit for restricted roads means that island, remote and rural communities can benefit just as much as the urban communities.
It is perhaps difficult to find any other initiative that increases liveability and public health that can be so universally adopted to all communities as a national default 20mph limit.
As a result, we would recommend it as an approach that particularly benefits island, rural and remote communities on the basis that without such a national intervention they may lag behind other more urban communities.
- Is there anything else that should be included or excluded from the Bill?
We applaud the Scottish Government in progressing this bill to its current stage. It provides a huge opportunity to align Scotland to what is becoming best practice across the world and especially in more socially aware countries. It aligns Scotland with such countries as Denmark, Norway, Netherlands, Sweden, Switzerland, France, Belgium, Austria, Germany and Japan where 30kmh is the accepted norm in communities whether urban or rural.
It will move Scotland away from the English model of inconsistent local setting of speed limits on built-up roads based on council priorities, values and empathy with communities. It will instead provide for a common national value of how roads are shared and do what national governments do best by setting those standards, facilitating implementation yet still allowing the flexibility for exceptions to be determined locally.
It will not be without its difficulties and there will be technical issues to overcome with the help of Transport Scotland, SCOTS and local authorities. However, we believe that national government has the vision to make its communities better places to be by implementing a 20mph limit as a default for built-up roads in communities. It is cost effective, beneficial and ultimately self-funding.
20’s Plenty for Us would be pleased to assist in any way that it can.
Rod King MBE
Founder and Campaign Director
20’s Plenty for Us
 The aims of the Bill include: enhancement of road safety, changing driving culture and promoting compliance with speed limits, improving health outcomes and more active travel and addressing inequalities in casualties from road accidents between deprived and non-deprived areas and contributing to a reduction in pollution from vehicle emissions.
 WHO – Managing Speed Page 8 http://apps.who.int/iris/bitstream/10665/254760/1/WHO-NMH-NVI-17.7-eng.pdf?ua=1
 Global Network of Road Safety Legislators – Manifesto #4RoadSafety P14 https://www.grsproadsafety.org/wp-content/uploads/Manifesto4roadsafetyFINAL.pdf
 International Transport Forum – Speed and Crash Risk https://www.itf-oecd.org/sites/default/files/docs/speed-crash-risk.pdf
 Taylor, M. C., Lynam, D. A. and Baruya, A. (2000) The effects of drivers’ speed on the frequency of road accidents.
 British Social Attitudes Survey, Transport 2015 - https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/586193/british-social-attitudes-survey-2015.pdf
 20’s Plenty – Why only 2-3mph change in speeds - http://www.20splenty.org/why_only_2_3mph_change_in_ave_speeds
 DfT – Speed Compliance Statistics, GB: 2016 - https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/623261/vehicle-speed-compliance-statistics-2016.pdf
 Dorling - 20mph Limits For Cars in Residential Areas, by Shops and Schools - https://www.thebritishacademy.ac.uk/sites/default/files/Danny%20Dorling%20-%2020mph%20Speed%20Limits%20for%20Cars%20in%20Residential%20Areas%2C%20by%20Shops%20and%20Schools.pdf
 Wann, Poulter, Purcell -Reduced Sensitivity to Visual Looming Inflates the Risk Posed by Speeding Vehicles When Children Try to Cross the Road http://journals.sagepub.com/doi/full/10.1177/0956797611400917
 Williams, North, Imperial College London - An evaluation of the estimated impacts on vehicle emissions of a 20mph speed restriction in central London https://www.cityoflondon.gov.uk/business/environmental-health/environmental-protection/air-quality/Documents/speed-restriction-air-quality-report-2013-for-web.pdf