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Visionary Streets

Thousands worldwide are killed each day in road accidents.  About 700 are child pedestrians, most of them just trying to cross the street. 

The main purpose of this website is to minimise these figures. It presents innovative ways to do so based on rectifying visual errors by drivers and pedestrians.


Doug StewartTrained as a civil and mechanical engineer, I became traffic engineer for a regional council.  Given the remit to analyse and prevent road accidents, my suspicion that many  involved visual error introduced me to a fascinating interface between engineering and psychology that was largely unexplored.
Creating products based on patents for visual innovations enabled me to become an independent road safety consultant and to develop ideas that led to a doctorate in psychology at Aberdeen University. This unusual professional mix has produced significant advances in understanding why road accidents occur and how to prevent them.

I identified such errors as prime causes of road accidents in the course of research carried out since the 1970s. They are documented in several papers, notably those linked to this page. By bringing them together I hope to encourage further development and application, because the huge potential for making roads safer, especially for pedestrians, is largely untapped. Initially, however, my focus was on accidents at rural bends.

Deceptive Bends

I had noticed that as clusters of accidents developed on accident maps, anomalies became apparent.  One was that sharp bends often had fewer accidents than gentler ones on the same road, leading to the discovery that the shape of a bend rather than its severity could determine its accident rate.

The reason is that a flaw in bend design causes drivers to misjudge the curvature of a bend, maintain excessive speed, and crash.  Why this occurs, and how it could easily be rectified, is the theme of the paper "The case of the left-hand bend". Confirmation is provided in “A remedy for accidents at bends”.

Child's-eye view through original guardrail
Child's-eye view through original guardrail....

Concealment by Pedestrian Guardrails

That insight into the importance of perception led to another discovery. Although pedestrian guardrails significantly reduce accidents, their benefit is reduced if they block visibility, especially for children. The scale of this problem in Britain could explain why we used to have the worst record in Europe for deaths and injuries to child pedestrians.

After replacement by Visiflex
....then after replacement by Visiflex®


No guardrail provided satisfactory visibility so I invented one that did.  In its original form, Visirail®, it became the most widely used in Britain because its casualty savings were so great. Early research and development is covered in the paper “Pedestrian guardrails and accidents”.

Diagonal Crossing by Pedestrians

While it is obvious that improving visibility is beneficial, why high-visibility guardrails reduce accidents by as much as 80% was more puzzling.  Seeking an explanation, I identified another visual hazard.  Pedestrians frequently cross streets diagonally, but doing so can make them blind to traffic from one side.  Accident analysis affirmed that this is a key factor in the majority of pedestrian accidents.
The reason that high-visibility guardrails prevent most accidents, therefore, is that they discourage diagonal crossing, as discussed in “A clearer vision for pedestrian guardrails”. This paper presents further development in guardrail design, culminating in the replacement of Visirail by Visiflex®. It also challenges the naïve claim that removing guardrails will reduce casualties because pedestrians will be more careful.  This is nonsense, as can readily be demonstrated. Casualties would escalate by up to 400%, depending on type of guardrail. See "Guardrail Debate".

Research findings from my 1988 and 2007 papers clarify how best to use guardrails to prevent casualties.  Design procedures are proposed in “Creating Safer Streets”.  Any feedback on their use and effect would be welcome, to

Misjudgement of Distance to Pedestrians

Child pedestrians are not at risk only because of concealment, of course. A more subtle visual error by drivers could be the principal cause of collision with children.

That line of enquiry took me into the fascinating world of optic flow, the perceived motion of objects as an observer moves relative to them. Computer simulation at Aberdeen University revealed how our innate ability to interpret optic flow gives automatic warning of impending collision, but is unreliable for drivers.  They have to rely instead on judgment of distance, but this is distorted by a visual illusion.  Drivers tend to perceive child pedestrians as taller people, further away, which delays braking and increases risk.
The paper “Misperception of time-to-collision by drivers in pedestrian accidents” presents this hypothesis, shows that it causes more than half of all child pedestrian casualties, and suggests remedies.  A review of the paper in New Scientist, “Deadly illusion brings death on the roads”, is an easy introduction.

More information about this research and its application is provided by my doctoral thesis "Safety implications of driver misperception in road accidents involving child pedestrians".

Future Prospects

I have become convinced that visual errors are a critical factor in most road accidents.  Few road users or highway professionals are aware of them, however, so there is neither public concern nor government action to resolve them.
A further problem is that officialdom tends to lack enthusiasm for research that is liable to expose mistakes. So although the hazards highlighted in this website have been aggravated by errors and omissions in British design codes, these have not been rectified.

Equally irresponsible is the current trend to give precedence to architectural fashion over accident prevention, such as removing guardrails to prettify streets. Failure to check such absurd proposals by rigorous safety audits highlights the chronic need for a national research body empowered to investigate and improve road safety, as exemplified by the original Road Research  Laboratory.

To close on a lighter note, pedestrians may avoid road accidents by switching to alternative modes of travel. Regrettably one which I developed ("Mountain Sailing"), although fast, free and carbon-neutral has yet to pass a safety audit.


The difficulties of working as an independent researcher were greatly alleviated by my association with Aberdeen University.  Their encouragement to pursue radical research is much appreciated.  The backing of my patent licensees Hugh Logan and Danny Mackay has also been invaluable.
Above all, “the Lord was my support.  He brought me out into a spacious place”.  His input to my work has been extraordinary, as outlined in "The Light in the Tunnel".