Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 5
5 CHAPTER 2 State-of-the-Art Summary Urban areas present unique challenges to the roadway de- are crashes that involve a vehicle that leaves the roadway. signer. Urban and regional stakeholders need a transportation Of the 6.2 million crashes in 2005, run-off-road crashes network that allows them to accomplish their travel objec- accounted for 0.95 million, or about 15 percent of the total. tives with a minimum amount of travel delay and to have While run-off-road crashes happen less frequently than other these travel demands met on a road network that is both types of crashes, they are often severe. Although run-off-road operationally efficient and safe. crashes accounted for only 15 percent of all crashes in 2005, While the transportation profession has made dramatic they accounted for 32.2 percent of the total fatal crashes in advancements toward meeting safety and mobility mandates, that year (see Table 1). it is critical that the function of the street system complement Examining fatal crashes by the first harmful event illustrates the adjacent land use and balance the needs of all users while the magnitude of specific roadside hazards. Of the fatal crashes maintaining the safest possible transportation facility. Of par- occurring in 2005, 39 percent involved collisions between ticular interest is the design of roadsides--the area between motor vehicles. Rollover crashes and collisions with fixed the shoulder (or curb) and the edge of the right-of-way (1). objects--two kinds of crashes that are associated with the The roadside is a common location for pedestrian activity, roadside environment--made up 11 percent and 32 percent, utility placement, landscaping, transit stops, driveway place- respectively, of fatal crashes in 2005. The highest percentage ment, mailbox placement, and placement of a variety of other of fixed-object crashes was in the category of tree/shrub, with roadside features typical of the urban environment. Urban tree or shrub impacts accounting for slightly more than 3,200 roadside environments can range from dense downtown crashes, or roughly 8 percent of all fatal crashes. Poles and zones with on-street parking to high-speed zones with motor posts accounted for a little less than 5 percent of all fatal crashes vehicle operational priorities. (see Table 2). Given the importance of the roadside environment to the quality of urban life, it is unsurprising that urban residents Roadside Safety: Current Practices and stakeholders often seek to have the roadside designed in a manner that enhances the quality of the urban environment. The literature on roadside safety establishes three roadside Commonly requested functional roadside elements include crash strategies that can be considered when seeking to im- sidewalks, street trees, and street amenities such as seating. prove run-off-road crash statistics (1). First, the ideal scenario Requested aesthetic elements include public art and special is to prevent vehicles from leaving the travelway, thereby paving materials. Placing these roadside elements in a way eliminating the crash entirely. Preventing the conditions that that enhances urban roadside safety is the focus of this liter- lead to run-off-road crashes (conditions such as driving while ature review. impaired or fatigued) and alerting a driver that he or she is leaving the travelway would be potential countermeasures included in this category. Overview of Roadside The second strategy, which is based on the idea that run- Crash Statistics off-road events are impossible to prevent entirely, is to design In 2005, over 6.2 million crashes occurred on U.S. roadways. a roadside that is "forgiving." In other words, a roadside Almost 1.9 million of these crashes involved an injury, and should be designed to minimize the consequences of a run- 39,189 people were fatally injured (2). Of particular concern off-road event. Under current practice, the ideal roadside
OCR for page 5
6 Table 1. Crashes by number of vehicles and relation to roadway (2005). On Run-Off- Other/ % Run- Crash Type Roadway Road Shoulder Median Unknown Off-Road Total Fatal Crashes Single Vehicle 6,507 12,340 2,431 1,022 353 54.5 22,653 Multiple Vehicle 15,647 297 302 198 92 1.8 16,536 Total 22,154 12,637 2,733 1,220 445 32.2 39,189 Injury Crashes Single Vehicle 154,000 320,000 14,000 48,000 28,000 56.7 564,000 Multiple Vehicle 1,235,000 7,000 1,000 7,000 2,000 0.6 1,252,000 Total 1,390,000 327,000 16,000 54,000 30,000 18.0 1,816,000 Property-Damage-Only Crashes Single Vehicle 328,000 598,000 31,000 81,000 277,000 45.5 1,314,000 Multiple Vehicle 2,957,000 11,000 3,000 14,000 5,000 0.4 2,990,000 Total 3,284,000 609,000 34,000 94,000 282,000 14.1 4,304,000 All Crashes Single Vehicle 488,000 930,000 48,000 129,000 306,000 48.9 1,900,653 Multiple Vehicle 4,208,000 18,000 5,000 21,000 7,000 0.4 4,258,536 Total 4,697,000 948,000 53,000 150,000 313,000 15.4 6,159,189 Source: Adapted from Traffic Safety Facts 2005 (2). allows errant vehicles to come to a controlled stop before design treatments, leaving the definition of what constitutes encountering an object located along the roadside by includ- a "safe" facility open to question. The ability to clearly and ing a clear zone adjacent to the travelway. In many situations, reasonably evaluate and demonstrate the safety impacts will however, such as urban roadways located in narrow rights- go a long way toward resolving many of the contentious issues of-way, a clear zone may be impractical. Thus, in many cases, that relate to the design of urban roadways and toward satis- in which the provision of a clear zone and/or wider right-of- fying the needs and interests of project stakeholders. This re- way may be desirable from a safety perspective, achieving this view, therefore, summarizes focused research on the safety of clear zone may be infeasible. Under these circumstances, roadside treatments in urban areas with particular attention design agencies should strive to minimize the severity of an to the high-speed (thus more severe) crash locations such as impact with a fixed object should such a crash occur. suburban-to-urban arterial transitions where land use is less This literature review summarizes known roadside design dense, on-street parking is rarely permitted, and the presence safety guidance for roadways in urban areas. There is often of driveways/intersections is considerably less frequent than little substantive knowledge on the safety impacts of various it is in more congested urban business corridors. Table 2. Fatal crashes by most harmful event (2005). First Harmful Event Fatal Crashes % of All Fatalities Collision with Motor Vehicle in Transport 15,357 39.2 Pedestrian 4,520 11.5 Object Not Fixed Bicycle 776 2.0 Other Object Not Fixed 1,209 3.1 Overturn (Rollover) 4,266 10.9 Tree/Shrub 3,215 8.2 Pole or Post 1,852 4.7 Culvert/Ditch/Curb 2,591 6.6 Fixed Object Embankment 1,444 3.7 Guardrail 1,189 3.0 Bridge 336 0.9 Other Fixed Object 1,812 4.6 Other Unknown First Harmful Events 622 1.6 Total 39,189 100.0 Source: Adapted from Traffic Safety Facts 2005 (2).