17. Pedestrian Barriers
Fatal Accident Reporting System data from the United States Department of Transportation show a consistent pattern of about 15 percent of all deaths occurring each year as a result of vehicles striking pedestrians.1 In urban areas, approximately 25 to 50 percent of traffic deaths involve pedestrians. Many countermeasures are available to deter or inhibit vehicle-pedestrian conflicts, including the use of barriers of various kinds primarily to discourage pedestrians from making dangerous, unauthorized movements into the roadway.
At some locations, crossing a street would expose the pedestrian to a very high risk of being struck by a motor vehicle. In these instances, the preferred treatment consists of modifying or reconstruction the roadway to make it safer for pedestrians to cross. However, in extreme cases where this is not practical it may be necessary to prohibit certain pedestrian crossings. Since signs ("DO NOT CROSS HERE") are often ineffective, barriers should be considered to direct pedestrians away from hazardous crossing (figure8-1). Sites where barriers may be justified include:
Barriers should be placed at locations that most effectively prevent pedestrians from crossing streets at undesirable points, and that direst them to alternative crossings. They should be placed several feet from the travel lane to minimize the chances that they will be struck by a motor vehicle. Barriers may be built out of railings, chain links, or other materials, as appropriate. They need to be of sufficient height to prevent pedestrians from easily climbing over or under them.
At least several hundred fatalities are the result of vehicles leaving the traveled way or where other vehicle-pedestrian conflicts are involved that can be controlled in some instances through the use of positive, or crashworthy, barriers. Appropriate positive barriers, both permanent and temporary installations, can often secure substantial long-term benefits in protecting pedestrians from vehicle impacts. However, since the institution of crashworthy barriers primarily for pedestrians protection may be an expensive capital investment requiring subsequent long term maintenance of the systems, careful engineering analyses of need and cost -effectiveness should govern the decision on installations. As a result, these decisions must be guided by confirmation of a high potential for vehicles encroachments into a given pedestrian space.
Universal warrants for pedestrian barriers do not presently exist in any nationally recognized manual or study, although there has been acknowledgement of the generic problem of separating pedestrians from vehicle movements.
With respect to positive or crashworthy barriers, all contemporary engineering guidance as related to vehicle characteristics and motorist safety is fairly specific. 3,4 However, only two sets of current engineering specifications that are nationally applicable deal directly with the special needs of pedestrians. 5,6 These publications are entirely confined to bridges with pedestrian walkways. Consequently, careful engineering judgment must discern the highway street , and bridge locations where the potential is especially high for vehicle intrusion into pedestrian areas. The chances of significant vehicle encroachment into a pedestrian space is a function of three principal considerations:
The following sites hold typically be evaluated for possible barrier installations; it should be stressed that collateral benefit to bicyclists often accrue when a n affirmative decision is made to install a barrier system:
It should be stressed that curbs alone do not constitute a barrier to protect pedestrians from an errant vehicle. Except at very low speeds and shallow angles of impact, vertical curbs up to a foot or more in height can be readily mounted or ramped by errant vehicles. Although curbs provide important channelizing information to the motorist and serve as visual deterrents to leaving the travelway, they cannot substitute for positive barriers at sites where the later clearly are needed.
However, because barrier systems are generally designed to contain and redirect vehicles even at prevailing freeway speeds, they are costly for application to lower-speed facilities, particularly in urban and suburban locations where a barriers, which may be less costly, whose economy and tested performance to date show significant promise for use in low to moderate speed conditions in preventing vehicle impacts with pedestrians.
Work zone barriers are a special application of barrier technology and engineering judgment. The high level of exposure of both workers and pedestrians to adjacent vehicles, particularly in urban and suburban traffic conditions, often warrants the expense and labor involved in deploying and maintaining temporary barriers. Where temporary barriers protection is needed in a work zone for pedestrian safety, only certified systems with known performance should be used. Contractor-constructed wooden railing and chain link fencing are examples of unacceptable substitutes when placed close to traffic: they cannot prevent vehicle intrusion and they fragment or distort on impact and may be dangerous to pedestrians and workers.
As in the case with permanent barrier installations, low deflection and prevention of vehicle intrusion into the work zone an designated pedestrian areas are the main targets in the use of temporary barriers, and these aims are often met by the installations of portable concrete systems. Usually constructed in segments of 12 to 20 feet in length the two most important considerations in the use of temporary concrete and other low-deflection systems (e.g., guardrail with closely spaced, rigid posts) is, first, to avoid the use of short, intermittent segments, and second to ensure that the up-stream, leading ends of each longitudinal barrier run are properly flared and/or protected by impact attenuators.4 Improperly connected or unconnected short runs of barriers are unable to perform properly in containing and redirecting vehicles on impact and frequently increase the severity of accidents to both vehicle occupants as well as to workers or pedestrians. Moreover, the use of may short runs of barriers encourages the presence of unprotected, blunt leading ends.
In summary, the determination of need for positive barrier protection of pedestrians must be a product of a careful analysis of the ensuring benefits of installation based on the realization that any barrier system constitutes by itself an additional fixed-object hazard. The decision to use a barrier sometimes leads to a significant increase in property damage and motorist injury accidents and m therefore, the the judicious engineer should carefully gauge the tradeoff value of increased pedestrian protection against the potential for the disbenefits of motor vehicle barrier impacts. Most importantly, if a barrier is chosen for pedestrian safety reasons. it must be correctly installed and maintained. Improper installation or rehabilitation can effectively negate an projected increase in pedestrian protection and can also aggravate both the frequency and severity of vehicle accidents.