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Technical Foundation and Context
 
Roadway Departures
 
When we think about crash risk in road use, we generally think about collisions between road users, ether as vehicle occupants or as cyclists and pedestrians. Collision statistics however, suggest we must think more broadly.
 

 Figure 1 -  Car hit while parked in a driveway
 
About one in five single and multi-vehicle collisions involves at least one vehicle departing the roadway, and potentially interacting with roadside hazards or rolling over. Those 20% of collisions are responsible for almost half of all occupant fatalities on roadways. They also have a much higher proportion of injuries than other crash types, making roadway departures a significant source of occupant risk.

Figure 2 (L) Vehicle in the ditch following a snow storm

In response, roadside safety design pursues two parallel tracks. The proactive track involves trying to keep vehicles on the road and out of the roadside. The reactive or pragmatic track recognizes that vehicles will inevitably depart the roadway from time-to-time, and strives to provide a relatively safe place to crash.
 
Keeping vehicles on the road involves: predictable and consistent geometric design; positive speed and path guidance using both road message and traffic control devices; and opportunities for recovery from lane departures such as flush medians and paved shoulders. In the roadside safety field however, it is not a question of whether a vehicle will leave the roadway at a particular location, it is simply a question of how long before it occurs.
 
Minimum Roadside Clear Zones
 
To address this inevitability, roadside design is founded on the concept of minimum roadside clear zones, and a range of hazard mitigation measures arranged in declining order of preference. Clear zones, as the term implies, are areas alongside the roadway which are free of fixed object and terrain hazards. Zone width is design speed dependent and based upon empirical studies of how far along and how far into the roadside vehicles typically penetrate when they leave the roadway.

Roadside Safety Manual, Ministry of Transportation 1993 Roadside Safety Manual, Ministry of Transportation 1993  
Figure 3 (L) Vehicle intrusion into roadside at different design speeds; (R) Example of roadside clear zone
 
Where roadside clear zones cannot reasonably achieved by removing or relocating hazards, by flattening terrain and reducing the steepness of side-slopes, or by making hazardous elements traversable or crashworthy (e.g. breakaway), then shielding road users from the remaining hazards by means of barriers, end-treatments, and crash cushions may be appropriate.
 
Roadside Safety Systems
 
Roadside safety systems are designed to prevent vehicles from reaching the hazard they are intended to shield. They must be integrated with other roadway design elements in order to function correctly. Approaching ends and leaving ends must be designed to prevent the barrier system from spearing or penetrating the vehicle’s occupant space. Transitions must smoothly “hand-off” an impacting vehicle from one system to another – at bridges with parapet walls and approach-fill guide rails, for example.
 
Figure 4 Pocketing occurs when the mechanical connection between two barrier systems is insufficient to withstand a vehicle impact
 
Designing, constructing, and inspecting roadside protection systems intended to shield road users from hazards is a specialized task. The MTO Roadside Safety Manual and the AASHTO Roadside Design Guide provide policy, standards, guidelines, and best-practices.
                                                  
Roadside Safety Manual, Ministry of Transportation 1993 Roadside Design Guide, American Association of Ste Highway and Transportation Officials 2006  
Figure 5 (L) MTO Roadside Safety Manual; (R) AASHTO (US) Roadside Design Guide
 
Roadside design begins from the somewhat-unique perspective that a crash is already underway and unavoidable. It then looks at the likely trajectory of errant vehicles, and the hazards they may encounter, and sets out to make any interactions survivable. Once clear zone options are exhausted, this often involves the introduction of a roadside barrier.
 
Constructing roadside design features is straightforward, but relies on attention to detail, as proper assembly and grading details are essential to their effective operation in a crash.
 
Inspecting roadside safety systems and identifying roadside hazards potentially requiring treatment requires a thorough understanding clear zone policy and of past and current standards applicable to roadside safety systems, as roadside safety is very much an evolving field.
 
Figure 6 (L) Integration of lighting with guide rail has been overlooked; (R) Guide rail has been installed below standard mounting height (and a serious roadside fashion faux pas – no vest - has been committed)
 
Roadside barriers are not a panacea. Like other roadside hazards they present their own set of risks to road users. Impacts with barriers, end treatments, and crash cushions are generally less likely to result in occupant injuries, but cannot guarantee that they will not occur. The use of barriers therefore is only justifiable when the estimated risk associated with impacting the barrier is less than the comparable risk of impacting the hazard it shields. The axiom for roadside designers is “Barrier where necessary, but not necessarily barrier.”
 
The Human Factor
 
To fulfil their function, roadside safety systems, along with the impacting vehicle’s crashworthy structure, must manage deceleration forces on occupants by collapsing and absorbing energy. Humans can withstand incredible deceleration forces for short periods of time without serious injury, provided they are properly cushioned and restrained by modern car seats, safety belts, and air-bags.

Energy Absorption Systems Inc. 2015-05-06  
Figure 7 (L) Crash cushions like QUADGUARD collapse on impact and decelerate passenger vehicles.
 
Space shuttle astronauts experience about 4x normal gravity at launch. Interactions with roadside safety systems at highway speeds result in forces 3x higher (about 12g), but only for a second or less. Drivers racing the latest generation of Formula 1, Indy-car, and NASCAR vehicles have survived motor-sports crashes into SAFER, energy-absorbing trackside barriers at speeds approaching 200 mph, resulting in momentary decelerations approaching 90g.
 
Testing and Certification
 
Sophisticated on-road crash cushions, like the QUADTREND and QUADGUARD, are computer-designed and performance-tested in full-scale crash simulations before being approved for use on public highways. These devices are used extensively on Ontario roads and highways, and are designed to work in concert with vehicle occupant protection systems.
 
Texas A&M Institute Figure 8 Despite the sudden stop, and the damage to both vehicle and attenuator, the occupant space is not breached, and the deceleration forces - although unpleasant - are survivable for a belted occupant
 
Struck head-on, such systems can decelerate a car or light truck from 100 km/h to rest in less than eight (8) metres, while maintaining tolerable deceleration forces. Empirical testing, computerized crash modeling and real-world experience suggests that, although your vehicle will unquestionably be totalled, you will walk away with no more than minimal strain injuries from such a crash about 85% of the time.
 
Concrete safety-shape barriers, despite having no apparent energy-absorbing qualities, remain highly-effective in minimizing occupant injuries due to the sophisticated design and finish of their impact face. Errant vehicles typically strike barriers at an angle. In the case of the concrete safety-shape, the impacting vehicle’s energy is dissipated as it slides along and repeatedly tries to climb the face of the barrier and over-turn, only to lose traction and slide back down, beginning the process over again. While the vehicle slides along and oscillates up and down, dissipating energy, the concrete barrier keeps it from being directed back into traffic, eventually bringing the vehicle to rest.
 
Surprisingly, due to the smooth ramped face, most of the vehicle-to-barrier contact involves only the vehicles’ tires; bodywork damage is usually minimal, particularly in low-angle crashes. The barrier is so effective at minimizing injuries and damage that studies by the MTO of barrier-involved crashes on Highway 401 indicate that only about one (1) in twenty (20) impacts results in a reportable collision. Vehicles remain driveable (wheel-alignment notwithstanding) and subsequently leave the scene in the under their own power in the vast majority of incidents.
 
Texas A&M Institute Figure 9 (L) Concrete safety shape containing a light vehicle; (R) Not all concrete appurtenances are crashworthy
 
Evolving Needs
 
While many current barrier systems, end treatments, and crash cushions have remained effective despite changes in vehicle size and design, one system has aged poorly – three-cable barrier. While inexpensive to install, it is: not suited to installation on tight horizontal curves or narrow cross-sections; susceptible to damage from nuisance-hits, winter maintenance activities, and freeze-thaw action; and is requiring of frequent inspection and maintenance – ensuring that the cable mounting height is correct and the cables are taut - but these requirements are often overlooked.
 
Three-cable barrier performance is heavily influenced by mounting height and cable tension, but even when in a state of good repair, its performance when struck by vehicles with low hood-heights and by larger SUVs is less than optimal.

Figure 10 (L) Guiderail; (R) a high centre-of-gravity may compromise three-cable guide rail performance
 
Developed in the 1940’s, three-cable barrier worked well with the up-right, square-bodied, steel-fender vehicles of the time. Despite their small contact area, the cables could engage with these robust vehicles and guide them to a halt without cutting into the occupant area.
 
With modern vehicles however, low hood-heights for aerodynamics on passenger vehicles are resulting in more under-rides of the cables, with the vehicle becoming wedged underneath the system. Lower belt-lines mean the cables are engaging at the level of the side windows, with the door pillars rather than the doors themselves.
                                                         
WSDOT Headquarters Washington State Department of Transportation WSDOT Headquarters Washington State Department of Transportation  
Figure 11 A modern full-sized car strikes three-cable guide rail and begins to under-ride it. Note the amount of lateral deflection of the system which occurs upon impact
 
Meanwhile, the popularity of SUVs, with their larger tires and higher centre-of-gravity, is resulting in more frequent over-rides and roll-overs associated with three-cable guide rails. Increasingly, instead of engaging, these vehicles are depressing the cables, particularly if their mounting height is low and/or they are slack to begin with, and the vehicle is passing over the system unrestrained.
 
Figure 12 (L) Three-cable guide rail in disrepair; (R) Improper transition between three-cable and steel beam guide rails
 
Even when the cables successfully engage along the side of these vehicles, the combination of centre-of-gravity, cable mounting height, and the stretching/deflecting of the cables, is resulting in vehicles rolling over the system laterally, and often down any embankments beyond. Accordingly, many progressive road authorities are categorizing three-cable guide rail as obsolescent, refraining from undertaking any new installations, and are replacing existing installations with steel-beam guide rail when the end of their service life is reached.
 
Summary
 
Attention to roadside safety issues has the potential to cost-effectively reduce injuries and fatalities associated with roadway departure crashes by keeping more vehicles on the road and giving those that inevitably leave the roadway safer places to crash.
 
Management of these critical safety assets benefits from specialized knowledge in traffic engineering; applied human factors; and positive guidance; along with roadside safety systems design, construction, inspection, and deficiency mitigation.
 
Specialists in road safety science, asset management best-practices, societal collision reduction benefits, and remediation cost estimating are increasingly using this information and expertise to generate economically-sound business cases for action on behalf of road authorities.
 
Figure 13 - Cluster of four (4) fatality markers, erected by the public following a roll-over, alongside a curve in a northern Ontario highway. The four casualties were occupants of the same vehicle; none were out of their teens. A missing curve warning sign may have contributed to the incident.
 
As collision statistics and first-hand observations such as the above confirm, there is still much to do.
 
The Project
 
In late 2014 York Region selected the Traffic Operations Business Unit within CEG, supported by Associated Engineering Group Limited, to undertake a three-phase roadside safety improvement program applicable to all regional roads.
 
Phase I
 
Phase I involved a comprehensive roadside safety asset inventory, a condition assessment, and an inventory of unshielded hazards. This required locating, characterizing, and conducting a detailed inspection of over 2,300 safety systems and unprotected roadside hazards across the Region’s road network.

Figure 14 (L) Example of a leaving end treatment having been hit and in need of repair; (R) Example of an incorrect and thus weak steel beam to bridge parapet transition
 
Phase II
 

Under Phase II, the asset management database created in Phase I was analyzed to identify and prioritize opportunities for safety improvement based upon their potential to reduce the risk of injuries to road users. Site-specific risk scores, mitigation strategies and high-level implementation costs were developed for each improvement opportunity location. This information was then rolled-up to estimate: total asset replacement costs; useful life; unfunded maintenance backlogs, and annual state-of-good-repair funding requirements.

Figure 15 Analysis of field-collected data
 
Taken together, the data has served to populate the Region’s CityWorks asset management decision support tool, and the analysis has provides the basis for a project report and a planned presentation to Regional Council to petition for project funding. This will address both the accrued maintenance deficit, and go-forward annual maintenance needs.

Figure 16 Phase II determined metrics including: (L) total asset value; and (R) risk-based priority for remediation
 
Phase III (pending)
 
Under a pending Phase III, the Transportation Infrastructure group within CEG will prepare up to 300 design sketches detailing the site-specific mitigation treatments being recommended, to be assembled and tendered for construction by the Region in accordance with available funding.

Figure 17 Examples of: (L) Remedial work completed on a steel beam to concrete parapet wall transition; and (R) retrofitted steel beam guide rail approaching end treatment
 

Future Opportunities
 
This is the second major roadside safety improvement project upon which CEG and AE have collaborated; the first having been for the Municipality of Chatham-Kent. These projects have leveraged our roadside safety expertise along with AE’s asset management expertise, and have provided an opportunity to: develop task-specific data collection and management tools; train staff in assessing roadside safety devices; and systematize analysis requirements such as relative risk modeling.
 
As more and more jurisdictions turn their attention to roadside safety improvement and asset management, our CEG/AE team is uniquely positioned to demonstrate the required expertise and the ability to deliver similar projects cost-effectively.

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