By Said M. Easa, P.Eng.
Traffic collisions worldwide ranked ninth among leading causes of death in 1990. By 2020 they will rank third behind only heart disease and strokes, according to a study carried out by the Harvard Uni...
Traffic collisions worldwide ranked ninth among leading causes of death in 1990. By 2020 they will rank third behind only heart disease and strokes, according to a study carried out by the Harvard University Center for Population and Development Studies. The economic and social impacts of road collisions affect communities at many levels. There is not just the personal suffering of individuals, but also the loss of productivity, and high health care and insurance costs.
What is wrong with our highways? Many people asked that question following the unprecedented number of collisions on Highway 401 near Windsor, Ontario last year. The answer is complex because road collisions are caused by many factors, including human error, speeding, environmental conditions and road design.
The last factor, of course, is the one over which consulting engineers have the most direct influence. Recently there have been developments in geometric road design and advanced technologies that will have far-reaching implications on safety. Nonetheless, we need broad-based, creative solutions that include not only sound road design, but also enforcement. Solutions also have to include driver awareness, education, and administration.
The Transportation Association of Canada (TAC) published a design guide in 1999, entitled Geometric Design Guide for Canadian Roads.
The two-volume guide, which replaces and updates earlier guides, introduces important material that reflects evolving knowledge. Such topics include truck escape ramps, roundabouts, roadside safety, rumble strips, and pedestrian access and safety. In particular the guide stresses the importance of the “forgiving roadside” that allows the driver of an errant vehicle to recover and avoid a crash, or at least to minimize the severity of the impact.
The guide introduces several key concepts. One, design domain, refers to a range of values that a design parameter might take. The main benefits of the concept are that it reinforces the need to consider trade-offs within the domain rather than simply meeting standards.
A new procedure for evaluating the costs and benefits of safety is included. It uses collision frequency, expressed as collisions/year or collisions/kilometre-year, instead of the old practice based on collision rate, expressed as collisions/million-vehicle-kilometres. Although the collision rate is commonly used in practice, it may lead to ambiguity. The new procedure relies on safety performance functions that relate collision frequency to average daily traffic, with parameters that vary for different highway classes. The guide also addresses aspects such as collision types and collision costs.
Another key feature is the explicit evaluation of safety for design elements like horizontal alignment, vertical alignment, and truck climbing lanes. The safety implications of many other elements are not included because there is still not enough meaningful data. Nonetheless, this guide is the first attempt to compile this knowledge for Canadian road designers.
Design consistency is the subject of a new chapter, referring to the characteristics and performance of successive roadway elements in two-lane highways. The book suggests three principles by which the designer could evaluate consistency: cross section, operating speed, and driver workload. Operating speed consistency, which is the most well developed concept, is based on the variation of operating speed from one geometric element to another, e.g. from a tangent to a curve. The greater and more frequent are the speed variations along the road, the higher is the risk of collision. A more comprehensive review of design consistency is in State of the Art of Highway Geometric Design Consistency, J. Transp. Engrg., ASCE, 125(4), 1999.
One development the guide does not address relates to sight distance analysis of three-dimensional alignments, where horizontal and vertical curves overlap. Research by the writer and associates has shown that alignment design based on current two-dimensional practice is generally conservative, but could be inadequate for some alignment combinations. Innovative scientific tools for safety evaluation are also emerging at the University of British Columbia. Also, the guide gives little guidance on low-volume roads. Since these constitute most Canadian roads, it is satisfying to know that TAC is funding a project to develop this chapter.
Overall, the TAC guide is an excellent reference and essential document for consulting engineers involved in road design and construction.
Another new valuable tool for highway designers is from the Ministry of Transportation of Ontario (MTO). The Ministry has implemented a process to refine the evaluation of highway improvements which is detailed in the 1999 report, The Science of Highway Safety: Network Evaluation and Safety Conscious Approach.” The process includes up-to-date knowledge about highway safety and supporting tools to systematically incorporate safety into practice.
The Ontario Ministry’s definition of safety is the same as the TAC guide definition. However, the parameters have already been estimated using Ontario highway data. Therefore, the MTO report might be useful for other provinces that wish to implement the new safety concept of the TAC guide. The report also shows how human factors affect engineering considerations in ways previously unknown.
Road safety audits
The road safety audit, a concept first developed in Australia, New Zealand and the United Kingdom, was introduced to North America in 1997. The principle behind such audits is that changes in drawings at the design stage are much easier than rebuilding costly infrastructure. However, an audit can be done of both proposed and existing roads.
A road safety audit is a formal and independent review of a road design by an expert safety team to assess the multi-modal safety performance of the design. The outcome is a report identifying any safety concerns and suggesting safer alternatives. A design safety review serves the same purpose as an audit, but is informal and interactive in nature.
The first road safety audit in British Columbia was conducted early in 1997 by Hamilton Associates for the Highway 1 project on high-occupancy vehicle lanes. Subsequently, several road safety audits have been done in the province for major highways, bridges, and interchanges. Given the time and budget pressures typically imposed on such projects, safety audits are now seen as a critical component of road design.
Outside British Columbia, several Canadian provinces are also gaining experience in road safety audits. In Ontario, for example, the pre-opening safety review of Highway 407, north of Toronto, was undertaken early in 1997. While not formally an audit, the review received national media attention and helped transportation engineers to focus on the importance of explicitly accounting for road safety at the design stage. Road safety audits (called assessments in Ontario) are part of the MTO refined process mentioned earlier. In New Brunswick, a safety audit was prepared in 1997 for the Fredericton-Moncton Highway design-build project as part of the proposal preparation stage, and road safety audits are being conducted during the detailed design stage. (See www.roadsafetyaudit.com).
Tools to slow us down
Advanced technologies can reduce the collisions caused by human errors or violations. Speeding is one of the most prevalent causes of traffic crashes. Whether it is exceeding the posted limit, or driving too fast for the conditions, speeding reduces the driver’s ability to steer safely around curves or objects and increases the distance required to stop the vehicle or react to a dangerous situation. The danger is heightened when the speeding vehicle is a large truck. A recent study found that roughly 22% of large truck fatal crashes involving multiple vehicles are related to speeding.
Technologies related to controlling speeding are becoming a common part of the road infrastructure in Europe and need to be introduced to Nor
th America. Based on a tour of Sweden, Germany, France, and England, the U.S. Federal Highway Administration has identified European practices that should and could be implemented here. Its 1999 report, Innovative Traffic Control Technology and Practice in Europe, recommended several initiatives for highways. These include:
Variable Speed Control. Safety could be much improved using variable speed limits. The system adjusts the regulatory speed limit using variable message signs. Automated cameras enforce the system.
Although variable speed control is currently based on real-time traffic conditions detected by loop sensors, future technology might be able to sense weather conditions on the road ahead and adjust the speed limits accordingly. In this way, for example, dense fog patches could be detected and the hidden hazard avoided. “We should have pulled over. The fog was terrible. Because I made it through the previous patch, I was thinking maybe I can make it through this one as well,” said one survivor of a multiple-vehicle pile-up on Highway 401 last fall.
Intelligent Speed Adaptation. This system can directly or indirectly influence the speed of vehicles in target areas where vehicles are monitored. When a vehicle speed exceeds a threshold, two options are possible. The system can set off an alarm within the vehicle to alert the driver to a speeding violation. Or the system can physically limit the speed of a vehicle by transmitting a road beacon signal to a receiver in the car. Field trials in Sweden showed that compliance with the speed limit increased from 20% to over 80%. More than 50% of the drivers said their comfort increased, and 75% felt the mental pressure was less. Almost 100% thought the system would lead to safer traffic, and interaction with other road users improved.
Automated Enforcement. This system combines radar or laser speed-measuring technology with a video or photographic identification to automatically detect and record speed limit violations. It is widely employed by European agencies, where enforcement cameras are mounted on the back of overhead highway signs in several classes of roadway. However, cameras for speeding have been controversial in Canada where people are more wary of intrusions on personal privacy.
Experience has shown that automated enforcement is key to making drivers comply with variable speed limits. The system has dramatically decreased (25% to 30%) the number of rear-end collisions at highway traffic jams. In urban areas, where the leading cause of vehicle crashes and injuries is the disregard of traffic lights, cameras are also being used to deter violations and penalize drivers who run red lights.
Intelligent transportation system (ITS) technologies that provide vehicles with the means to avoid crashes are also on the way. The smart vehicles of the near future will sense objects, avoid collisions, and monitor driver alertness. For example, lane guidance systems will be installed as standard equipment in Freightliner’s trucks this year. Their system uses a mini-camera mounted in the top centre of the windshield. An image of the road surface ahead is sent to a processor where it is scanned for lane markings. If the driver deviates from the lane, a synthesized rumble-strip noise from loudspeakers alerts him or her. The company will also install an automated system that warns the driver of an impending rollover. If necessary, it de-activates the throttle and applies the engine retarder. The system detects rollover by measuring the lateral forces (using the anti-lock braking system electronic control unit and accelerometers) and individual wheel speeds (using sensors). Field studies in British Columbia have shown these systems give a return on investment of 2:1 within five to 10 years.
Road safety is something that should be prevalent and considered in all business decisions, especially those made by governments. We expect governments to provide leadership to promote a safe highway system. They should ensure, for example, that the enormous competitive pressures in the trucking industry resulting from just-in-time inventory and globalization do not compromise public safety.
The cost of traffic collisions is rising both in human and economic terms. As a result, highway safety is starting to become an issue of worldwide concern, something like the growth of environmental awareness in the early 1990s. Such rising public interest demands that road authorities and consulting engineers face the challenge of improving safety on our roads. CCE
Said Easa is professor at Lakehead University and author of two chapters on “Geometric Design” and “Automated Highways,” published, respectively, in Civil Engineering Handbook, CRC Press, 1995 and the Encyclopaedia of Electrical and Electronics Engineering, John Wiley, 1999. He is also editor of Urban Planning and Development Applications of GIS, just published by the American Society of Civil Engineers.