Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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 58
58 APPENDIX C Toolkit for Urban Roadside Design Introduction Object placement strategies. Object placement strategies include the following: It is a challenge to design an urban roadside environment that balances the often conflicting demands of land owners, · Roads on tangent with vertical curb recommend lateral road users, and local jurisdictions to effectively use this valu- offset of 6 ft (absolute minimum of 4 ft) from curb face to able space without dramatically compromising safety. Though rigid objects [these values also apply to median locations]. there is still much to learn about how the urban roadside con- Frangible objects should be positioned no closer than 1.5 ft figuration influences the functional operation and safety of a to curb face. roadway corridor, some basic design concepts can help assure · Roads at horizontal curves with vertical curb recommend the placement of roadside objects that minimize potentially lateral offsets to objects a minimum of 6 ft from the curb hazardous conditions. This toolkit provides placement strate- face on the outside of curve face and a recommended lat- gies, referred to as urban control zones, for a variety of urban eral offset of 4 ft for the inside of curve locations (absolute conditions. The primary focus of this summary is roadside minimum of 1.5 ft for frangible items only) from curb face object placement for high speed urban roads. Roads charac- [these values also apply to median locations]. For sharp terized by twenty-four hour on-street parking or low speed curvature locations, determine an object free zone based local roads are not directly addressed in this toolkit. Follow- on sight distance criteria (see Figure C-1). ing the urban control zone section are treatment details for · Roads on tangent or curve with shoulder (no curb) adhere known objects common to the urban roadside environment. to clear zone guidelines where possible. If infeasible, then locate objects immediately adjacent to the right-of-way boundary to maximize lateral offset. Urban Control Zones · Auxiliary lanes that function as higher speed lanes such as An urban control zone is a roadside location that can be extended right-turn lanes must meet the tangent and curve shown to pose a greater hazard for errant vehicles and as such criteria. should be given special attention regarding object placement · Auxiliary lanes such as bicycle lanes can include the width strategies. Key urban control zones include lateral placement of the bicycle lane in the clear zone; however, it is still strategies, lane merge locations, driveways, intersections, and recommended that lateral offset from the curb face exceed sidewalk configurations. In addition high crash locations and 1.5 ft where possible at these locations. common roadside crash locations can also be identified as potential urban control zones for roadside safety. Lane Merge Locations Description. Often acceleration lanes, lane merges, and Lateral Placement of Objects bus bay exit points transition to the through travel lane at a Description. Where possible, achieve the clear zone as taper point. At this location, the driver of the vehicle needs to recommended by the AASHTO Roadside Design Guide. In focus on merging into the active traffic stream. If the driver constrained urban areas where clear zones are not feasible, does not judge the merge correctly, he or she may run off the the recommended lateral offset to roadside objects may vary road at this location. As a result, lane merge locations should depending on specific road features. be free of roadside objects where possible.
OCR for page 59
59 LEGEND Lateral Offset at Inside of Curve Std. Recommended 4' Lateral Offset 6' Curb Face 4' Lateral Offset Required Sight Distance along 4' Drivers' Line of Sight 4' Figure C-1. Lateral placement of objects at horizontal curves. Object placement strategies. Object placement strate- · Upstream (near side) placement of objects should be lo- gies include the following: cated so as to provide adequate sight distance for drivers of exiting vehicles. · Lateral offset of rigid objects should be as large as possible. Since the presumption is that a vehicle unable to traverse the lane merge will continue along its current path, a lateral off- Intersections set equivalent to a standard lane width should be kept free of Description. Though intersections are common crash rigid objects. Where feasible, therefore, objects should be locations for multiple vehicle collisions, numerous single placed at least 12 ft from the curb face so that errant vehicles vehicle roadside crashes can also be expected at intersections. unable to merge and that continue straight will not impact These collisions can occur because of the use of small islands the object. Breakaway objects should be located 4 to 6 ft from the curb face as a minimum at the taper point locations. · Longitudinal placement of rigid objects should not occur LEGEND within 10 ft upstream or downstream of the taper point for Lateral Offset at Taper Point a total length of 20 ft where feasible (see Figure C-2). Where this placement is infeasible, priority should be given Std. Recommended Lateral Offset to keeping the upstream roadside area object free. 4' Driveways Description. The placement of roadside objects in the vicinity of driveways should occur in such a way as not to Curb Face 10' compromise available sight distance or provide a clear path for errant vehicles to impact a rigid object on the far side of a 12' driveway entry. 10' 4' 4' Object placement strategies. Object placement strate- Offset extended to Intersect where feasible gies include the following: Lateral Offset configuration applies to Lane Merges, Acceleration Lanes, and Bus Bay Returns · Downstream (far side) placement of objects should be located 10 to 15 ft from the driveway throat edge (see Figure C-3). Figure C-2. Object-free zone at merge points.
OCR for page 60
60 LEGEND Lateral Offset due to Driveway Std. Recommended Lateral Offset 4' Curb Face 10' to 15' 4' Drivers' Line of Sight Drivers' Line of Sight 10' to 15' Offset at Far Side of Driveway Figure C-3. Roadside object-free zones at driveways. that are not noticeable to drivers, objects located too close the edge of lane as these locations do not have a curb to to the curb in the curb return region, and objects located help the driver realize that the vehicle has strayed from the directly aligned with pedestrian access ramps. designated path. · Many urban intersections with curb include directional Object placement strategies. Object placement strategies pedestrian access ramps at the intersection corners. For include the following: these locations, rigid objects should not be positioned so that errant vehicles are directed towards them along the · Research shows that curbs can provide a positive (visual) path of the access ramp. As a result, placement of pedes- guidance but have very little re-directional ability; there- trian buttons should either be located on a breakaway fore, curbs should be used at raised channelization islands pedestal pole adjacent to the directional ramp where pos- to assist with providing positive guidance to the driver. sible rather than on a rigid traffic signal pole. This will · Since research shows that sloping curbs can be traversable, enable the traffic signal pole placement to occur further their use at channelization islands as a means of restricting away from the curb return region. vehicle access is not recommended. · For intersection channelization islands (also known as corner islands), the island design should adhere to the Sidewalk Configurations AASHTO Geometric Design of Highways and Streets criteria Description. In urban environments, sidewalks are often (see their Exhibit 9-37 and 9-38). The island should be suf- attached directly to the curb. When this occurs, all fixed road- ficiently designed so as to be conspicuous to approaching side objects should be located beyond the sidewalk. Another drivers and should not encroach on vehicle paths. Simi- common sidewalk configuration includes a buffer strip be- larly, median noses should be conspicuous and designed so tween the curb and the sidewalk edge. For these locations, ob- as not to impede normal traffic operations. At both the jects are often located within this buffer strip. Care should be corner islands and the median noses, the placement of rigid taken to assure that objects placed in the buffer strip area do objects should be avoided completely. Only breakaway not become roadside hazards. devices should be constructed at these locations. · Often a turning vehicle does not successfully navigate the Object placement strategies. Object placement strate- designated turn path and strays onto the adjacent curb re- gies include the following: turn or shoulder. This situation often occurs for truck turning movements. Object placement at the inside edge of · For a buffer strip 3 to 4 ft wide, rigid objects should not be intersection turning movements should be as far as practi- constructed. Only frangible items such as breakaway signs cal from the curb face or lane edge. Similarly, for locations or forgiving landscaping treatments are appropriate for use without curb these values should be as far as possible from in these narrow buffer strips.
OCR for page 61
61 · Buffer strips that are 5 ft wide or greater should include landscape treatments may have for intersection, driveway, smaller roadside items such as forgiving landscaping treat- and stopping sight distance considerations. ments or ornamental trees (with canopies that do not impede on sight distance) in the region adjacent to the curb but be- Strategy summary. The placement criteria, in some cases, yond recommended lateral offsets. If it is infeasible to locate is based on the functional purpose or posted speed limits of more rigid objects such as light standards or utility poles adjacent roads. Common landscape placement issues include beyond the sidewalk, then their placement should be imme- the following: diately adjacent to the sidewalk so as to place them as far from the active travelway as possible. Under no circumstances, · Avoid placement in proximity to intersections as discussed however, should these objects be located within the sidewalk in the urban control zone section. boundaries as this space must be kept completely object free · Avoid placement in proximity to driveways as discussed in so that pedestrians can remain on their designated path. the urban control zone section. · At locations with isolated hazardous trees, consider re- moving these trees. High Crash Locations and Common · At locations with known hazardous trees that cannot Urban Roadside Crash Locations be relocated, shield the trees with safety barrier where Description. Many urban corridors are characterized by possible. unique physical features that may directly contribute to a · Lateral offset placement of trees and landscaping as dis- roadside crash. Though the urban control zones previously cussed in the urban control zone section. Where practical, identified capture most of the high roadside crash locations, use plant layering in front of the more rigid items. In the a specific design or operational characteristic for a road may event of an errant vehicle, this initial landscaping will func- also be a location that merits roadside crash mitigation. These tion as an energy dissipation device and slow down the locations can be identified by creating spot maps that demon- vehicle prior to impact with the more rigid tree. strate cluster crash locations that do not fall within the · Implement median planting strategies as discussed in the bounds of the previously identified urban control zones. lateral placement urban control zone section. · Maintaining a clear vision space, which is a space above Object placement strategies. Each high crash location that ground that preserves the lines of sight for drivers, bicy- fits the above description will have roadside safety improve- clists, and pedestrians. In general, this space should extend ment strategies unique to the specific feature contributing to vertically 1 to 3 m [3.3 to 10 ft]. These dimensions will as- the high crash numbers. As a result, placement strategies can in- sure clear sight distance for drivers in low-riding sports clude increased lateral offset, shielding, or reconstruction for cars as well as drivers in high trucks and buses. The "clear extreme cases. This must be evaluated on a case by case basis. vision space" then is essentially the space above shrub growth and below tree overhang. A low tree overhang can also create an obstacle for pedestrian access. Roadside Treatment Details · Longitudinal placement of trees and landscaping will help Several roadside treatments common to an urban environ- keep landscaping growth from encroaching on other func- ment can become roadside hazards if not properly positioned. tions of the roadside environment. In addition to longitu- The following summaries identify these common urban road- dinal placement strategies discussed in the urban control side features and placement strategies that may help enhance zone section, it is advisable to prohibit landscape place- safety at these locations. ment at a variety of other locations. One jurisdiction, for example, recommends that these placement strategies could include the separation of trees from underground utility Landscaping, Trees, Shrubs, lines by 1.5 m [5 ft] and a placement a minimum of 3.0 m and Plant Layering [10 ft] from utility poles with 4.6 m [15 ft] recommended. General information. Several types of roadside land- In addition, trees could be separated from street lights by scaping are commonly employed to enhance the aesthetics of 6.1 m [20 ft], from fire hydrants and alleys a distance of roadside environments. These treatments may include the 3.0 m [10 ft], and 1.5 m [5 ft] from water meters or utility placement of shrubs, street trees, or alternative treatments vaults. Additional longitudinal placement strategies may such as landscape berms. In addition to the concern of tra- be implemented to try and achieve uniform tree spacing. versability in the event that an errant vehicle encounters This spacing will depend on the specific tree characteristics roadside landscaping, a common issue regarding the safety of but could range from 7.6 to 15.2 m [25 to 50 ft]. Tree adjacent landscape treatments is sight distance and the impact canopies should not be positioned under service wires.
OCR for page 62
62 · The strategic placement of landscaping to influence the vi- objects if jurisdictions do not enforce guidelines about mailbox sual perception of a driver is a relatively new technique. type and placement. There are several crashworthy mailboxes Landscaping can be used to help visually delineate the that have been tested including standard boxes mounted on a downstream road and geometric features of that road. The 100 mm by 100 mm [4 in by 4 in] wooden post or a 38 mm use of landscaping for visual perception purposes can also [11/2 in] light-gauge pipe for mounting mailboxes, with these help create visual narrowing of the driver's field by gradu- posts embedded no deeper than 600 mm [24 in] into the ally tapering a tree line towards the road. ground. Mailboxes should further be mounted to their supports to prevent the mailbox from separating from the post during a crash event. Standard cluster mailboxes (as approved by U.S. Utility Poles, Posts, Light Standards Postal Service Standards) can also be used in urban regions. General information. Utility poles, posts, light poles, Many of the larger mail collection boxes fail safety requirements and similar vertical roadside treatments are some of the most and should be placed outside of clear recovery areas. common urban roadside hazards. The urban environment, by its very nature, can be expected to include these common Strategy summary. While making mailboxes crashwor- roadside objects. thy will satisfy safety associated with mailbox-related crashes, it is important to recognize that the placement of mailboxes Strategy summary (for utility poles). Several potential may have an important impact on the overall safety of the strategies can be considered for addressing roadside safety for roadway. The following recommendations detail appropriate utility pole placement. These include the following: placement of mailboxes: · Place utilities completely underground and remove the haz- · Mailboxes should not obstruct intersection sight distance. ardous poles. The removal of all poles in the urban roadside · Mailboxes should not be located directly on higher-speed environment may not be practical, but the placement of util- roadways, where stopping associated with mail delivery ities underground, where feasible, will minimize this hazard. and collection can lead to substantial speed differentials · Place poles as far as possible from the active travel lanes. Rec- between vehicles on the travelway, thereby increasing the ommended goals include specific pole lateral clearance based possibility of a rear-end collision. For higher-speed urban on speed limits. One jurisdiction suggested a pole offset strat- roads without curb where mailboxes are present, one option egy with a target goal of 3.6 m [12 ft] from face of curb to face is to provide a 2.4 m [8 ft] mailbox turnout lane adjacent of pole for all locations where possible. For speed limits to the travelway that will permit vehicles to leave the trav- greater than 56 km/h [35 mph] but not exceeding 72 km/h elway for mail collection and delivery purposes. Alterna- [45 mph], a lateral clearance of 2.4 m [8 ft] is acceptable. For tively, a minimum shoulder width for these higher-speed roads with posted speed limits less than or equal to 56 km/h roads of 1.8 m [6 ft] should be maintained at these locations. [35 mph], a lateral clearance of 1.8 [6 ft] is acceptable. A sec- · At curbed residential locations, mailboxes should be posi- ond jurisdiction recommends an offset greater than 2.4 m tioned so that the minimum distance from the roadside face [8 ft] for roads with speed limits of 40 to 55 km/h [25 to of the mailbox to the face of the curb is 150 mm [6 in], with 35 mph] and a lateral offset of 4.3 m [14 ft] for roads with a preferred offset ranging from 200 to 300 mm [8 to 12 in]. speed limits of 65 to 70 km/h [40 to 45 mph]. · Mailbox placement at driveways should be compatible · Locate poles away from access points where the pole may with the urban control zones previously defined. restrict sight distance or be easily impacted. · Shield rigid mailboxes. · Place poles on the inside of sharp horizontal curves · Add reflective object markers to improve nighttime visi- (as errant vehicles tend to continue straight towards the out- bility of mailboxes. side of curves), but be sure pole placement conforms with the urban control zone recommendations previously shown. · Locate poles on only one side of the road and place shared Safety Barriers utilities on poles where possible. General information. Roadside barriers are subject to · Use breakaway poles at select hazardous locations or shield NCHRP Report 350 testing criteria. There are several types of them with safety barrier. safety barriers that may be present in an urban environment. These include the following: Mailboxes · Barriers (flexible, semi-rigid, and rigid), General information. The placement of mailboxes in · Bridge Railings, and urban environments can result in new hazardous roadside · End Treatments (crash cushions and end terminals).
OCR for page 63
63 Generally, most of the research on safety barriers has been includes items placed adjacent to the road that are there to oriented towards the design of barriers and their placement to improve the adjacent land use or to improve transportation shield vehicles from hazardous roadside conditions. The Fed- operations. In some jurisdictions, street lights and signs are eral Highway Administration maintains a roadside hardware included in the category of street furniture; however, for the website that provides information about specific roadside hard- purposes of this review street furniture is considered to be ware that has been tested. This information is available at: http:// supplemental items such as benches, public art, trash recep- safety. fhwa.got.gov/roadway_dept/road_hardware/index.htm. tacles, phone booths, planters, bollards, fountains, kiosks, transit shelters, bicycle stands, etc. Often the placement of Strategy summary. In the urban environment, it may be these devices can obscure sight distance, so their location challenging to construct roadside barriers in the confined should not occur in the sight triangles of intersections or roadside space available. In locations with bicycle activity, for driveways. Many street furniture items are placed along the example, safety barriers located immediately adjacent to the right-of-way by the property-owners themselves, as in the road may expose cyclists to unnecessary risks as the barrier case of the placement of a sidewalk cafe in front of a restau- may result in a sensation of "squashing" the cyclist between rant, and are thus largely outside the engineer's control. the barrier and an adjacent motor vehicle. Similarly, barriers immediately adjacent to motor vehicle lanes cause vehicles to Strategy summary. Little is known about the safe place- shy away from the barrier, thereby adversely impacting traf- ment of street furniture. The following general recommen- fic operations. Finally, traffic barrier restricts pedestrian ac- dations should enhance roadside safety in these locations: tivity in an urban environment and requires careful design of openings for pedestrian crossings that include crashworthy · While maintaining its functional purpose, locate street fur- barrier end treatments. Due to the wide variety of potential niture as far from the street as possible. safety barriers that may be selected for use, the two references · Restrict street furniture placement to avoid sight distance identified above should be consulted for specific applications issues for road users. The Urban Control Zones previously for each barrier type. identified should be applied to all street furniture. · Where possible, deploy street furniture that meets basic crashworthy standards; however, concern for pedestrians Street Furniture has led to the use of fixed supports in some urban areas. General information. In many urban areas the use of Examples of sites where breakaway supports may be street furniture is a common approach to improving the aes- imprudent are sites adjacent to bus shelters or in areas of thetic and functional quality of a street. Street furniture extensive pedestrian concentration.