DelDOT Road Design Manual

Chapter Two Design Controls

Plans for roadway improvement projects • Are there wetlands, historic sites and are based on established geometric design districts or other environmentally sen- standards for the various elements that consti- sitive features that need to be pre- tute a roadway. These elements include road- served? way width, side slopes, curvature, and gradi- ents. Decisions on appropriate geometric stan- • What are future goals of the transporta- dards are influenced by the characteristics of tion network? the specific highway section to be improved. • What are the economic needs of the af- Each project area has its own unique charac- fected communities or area? teristics. Many of these are identified through the project development process, included in These characteristics serve as a basis for se- the Project Initiation and further defined in the lecting design standards. Chapter Three- project scope of work. These items need to be Design Standards presents the specific made a part of determining a project’s design geometric design standards adopted by the controls and are evaluated along with such Delaware Department of Transportation elements as: (DelDOT). • The social context of the communities and area within the affected project 2.1 OBJECTIVES OF DESIGN area. What are the perceived goals for CONTROLS creating a more livable community? Four basic objectives should be kept in • Will the design provide the expected mind: level of service and safety of the users? • Level of Service. The design should • What is the existing and future traffic provide a level of service appropriate for volume? the characteristics of the traffic that will be using the facility. • What is the anticipated operating speed? • Safety. The completed facility should present motorists with a safe • What are the terrain features? environment. Special consideration • What are the needs for access and mo- should be directed to avoiding bility along the facility? potentially hazardous situations. • Will the selected design controls pro- • Economics. The cost-effectiveness of tect or enhance the natural environ- proposed improvements must be ment? considered. Improvement standards higher than appropriate for a particular facility may result in increased

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facility may result in increased • Level of Service C − stable flow, but expenditures that could be spent more operation of individual users is effectively by improving additional road significantly affected by traffic; ability sections. to select speeds is reduced and maneuvering requires substantial • Context. Design features should be vigilance by the users. selected that are in balance with the social context of the community and • Level of Service D − high density surrounding area. This is accomplished approaching unstable flow. Speeds and by gathering and including information freedom to maneuver are severely from the public throughout the design restricted. Small increases in traffic process. A context sensitive design flow will generally cause operational advances the objectives of safety, problems. mobility, enhancement of the natural environment, and preservation of • Level of Service E − operating community values. Projects that conditions at or near capacity with improve the livability of the unstable flow. All speeds at a low and community or quality of the natural relatively uniform value. Freedom to environment are considered context maneuver is extremely difficult. sensitive. • Level of Service F − forced or breakdown flow. Traffic exceeds 2.2 LEVELS OF SERVICE capacity causing queues with stop-and- go waves, and operations are extremely In general terms, the level of service of a unstable. highway facility may be influenced by many factors, including surface condition and ride- The traffic flow rates that can be served at ability. From the standpoint of design controls, each level are termed “service flow rates.” the level of service is principally related to the Once a level of service has been identified as ease and convenience with which the highway applicable for design, the accompanying ser- facility can serve the expected volumes of traf- vice volume logically becomes the design ser- fic. vice flow rate, implying that if the traffic vol- ume using the facility exceeds that amount, The Transportation Research Board’s operating conditions will fall below the level (TRB) Highway Capacity Manual presents a of service for which the facility was de-signed. thorough discussion of the level of service A guide for selecting design levels of service concept. Six levels of service are established is shown in Figure 2-1. from level A (the highest) through level F (the lowest). More detailed guidelines for selecting ap- propriate levels of service are given in The general characteristics of the various AASHTO's A Policy on Geometric Design of levels of service are: Highways and Streets (commonly referred to as the “Green Book”) and TRB’s Highway • Level of Service A − free-flowing Capacity Manual (HCM). traffic; users virtually unaffected by other traffic, able to select desired speeds and maneuver unrestricted. • Level of Service B − reasonably free traffic flow; users able to select desired speeds, but with a slight decline in freedom to maneuver.

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Figure 2-1 The process of selecting a design speed is Guidelines for Selection of Design found in Chapter Three-Design Standards. Levels of Service 2.3.1 OPERATING SPEED Type of Area and Appropriate Highway Design Level of Service AASHTO defines operating speed as “the Type speed at which drivers are observed operating Rural Rural Urban their vehicles during free flow conditions. The Level Rolling and 85th percentile of the distribution of observed Suburban speeds is the most frequently used measure of Freeway B B C the operating speed associated with a particu- Arterial B B C Collector C C D lar location or geometric feature.” Local D D D 2.3.2 RUNNING SPEED 2.3 SPEED-RELATED Running speed is defined as the speed at CONTROLS which an individual vehicle travels over a Many design decisions are controlled by roadway section. Running speed is mathemati- the expected speed of vehicles on the facility, cally determined by dividing the length of particularly decisions related to required sight roadway being studied by the running time re- distance and maximum permissible curvature. quired for the vehicle to travel through the Geometric requirements normally will be less section. The average running speed of all ve- stringent with lower speeds in difficult terrain hicles is used to evaluate service levels and and in urban areas. The design objective is to road user costs. The average running speed provide a facility serving the users’ needs in a varies during the day depending upon the traf- safe and economical manner. The speed on a fic volume. Peak and off-peak values are used facility is related to many factors such as the in operation studies and in design; average physical characteristics of the roadway, the running speeds for an entire day are used in amount of roadside access and activity, the user cost and other economic analysis. weather, the volume of traffic, and legally es- tablished speed limitations. Roadways should 2.3.3 DESIGN SPEED be designed to allow most drivers to operate at their desired speed under normal weather con- For each proposed roadway, a design speed ditions. is selected to determine various geometric de- sign features such as curvature, superelevation There are three terms used to describe a rate, sight distance, and critical length of vehicle’s speed when using the roadway: (1) grades. The design speed should not be less operating speed, (2) running speed, and (3) de- than the anticipated normal operating speed sign speed. Each of these either directly or in- and at least 5 mph [10 km/h] above the posted directly plays a role in the design process. Op- speed. erating speed is used to measure and study the overall efficiency of the design (attained level Some design features, such as curvature, of service), individual roadway sections and superelevation, and sight distance, are directly selected roadway features. Running speed is a related to design speed. Other features, such as mathematical tool used to develop road user lane widths, the inclusion of shoulders, shoul- costs and level of service. Design speed is der widths, and clearances to obstacles, are not used in selecting design criteria, guidelines directly related to design speed but have a sig- and other elements that will control the design. nificant affect on driver speed. Drivers react to the physical limitations and traffic rather than

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the importance of the facility. When a change design speed. For example, terrain conditions in design speed is made, many elements of the may limit the overall design speed of a road- highway design will change accordingly. way section to 50 mph [80 km/h], but several long tangents within the section may encour- The selected design speed should be logical age much higher speeds. This situation should with respect to the characteristics of the ter- be recognized, and the curves at each end of rain, adjacent land use, and functional classifi- the tangent should be somewhat flatter than cation. A highway in level terrain may justify minimum standards for 50 mph [80 km/h] to a higher design speed than one in rolling ter- permit a vehicle’s safe transition back to the rain. A highway in lightly developed or unde- design speed. veloped (open) areas may justify a higher de- sign speed than in a developed area. The se- Similarly, if vertical curves on tangent sec- lected design speed should be consistent with tions are designed based on the 50 mph [80 the speeds that drivers are likely to expect on a km/h] stopping sight distance criteria, a danger given highway facility. exists when actual operating speeds may ex- ceed 50 mph [80 km/h]. Designers should an- A highway carrying a high volume of traf- ticipate locations where operating speeds may fic may justify a higher design speed than a exceed design speeds for certain situations, lower volume facility or a facility that is of a and should avoid applying minimum levels of lower functional category with similar topog- geometric standards in these locations. raphy. But a low design speed should not be assumed for a low volume road where the to- pography is such that drivers are likely to 2.4 TRAFFIC-RELATED travel at high speeds. This could lead to select- CONTROLS ing design criteria resulting in unsafe horizon- tal and vertical geometry for the user. The characteristics of the traffic expected on a particular facility are significant factors in Except for local streets where speed con- establishing many of the design controls for a trols features are included intentionally, every project. The primary traffic characteristics af- effort should be made to use a design speed as fecting design are volumes, the directional dis- high as practicable to obtain a desired degree tribution, the composition, and the future pro- of safety, mobility, and efficiency. In meeting jections for each of these elements. this objective the constraints of environmental quality, economics, aesthetics, and the social 2.4.1 TRAFFIC VOLUMES context of the impacted areas must be identi- fied and addressed. Above minimum design Traffic volumes are expressed in several values should be used where feasible, but the different ways: designer needs to recognize that project con- • Average Annual Daily Traffic (AADT). straints may lead to selecting a practical value. The total yearly volume divided by the Selecting higher or lower values that do not number of days in the year. reflect the driver's travel desires, habits, and expectations is not consistent with producing a • Average Daily Traffic (ADT). The total balanced project meeting all the associated volume during a given time period in constraints imposed on most projects. The de- whole days greater than one day and less sign speed selected should be inclusive of the than one year divided by the number of typically desired speed of the highest- days in that time period. percentile of drivers. • Peak-Hour Traffic (PHT). The traffic volume during an interval shorter than a It is necessary to recognize conditions where vehicle speeds typically may exceed the

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day, usually one hour, that reflects the sectional elements and the structural design of frequently repeated rush-hour periods. the pavement needed to withstand the traffic loads for the projected service life of the pro- • Design Hourly Volume (DHV). The ject. peak hourly volume expected in the 30th highest hour during the chosen design year. This helps give a better picture of 2.4.3 TRAFFIC PROJECTIONS unusual seasonal fluctuations or other conditions that may cause capacity For all projects involving new construction problems. or major reconstruction, the design controls normally will be based on the traffic volumes • Directional Distribution (D). A measure estimated for 20 years in the future, expressed of the highest traffic volume in one as either ADT or DHV. direction during peak hours, expressed as a percentage of the DHV. This is For projects where the scope of work is important principally with relatively limited to resurfacing, restoration, rehabilita- high traffic volumes where capacity is tion, and reconstruction improvements, the ca- being approached. pacity should be checked against the projected traffic volumes for the forecast year (normally Information on traffic data, including the not to exceed 10 years). The forecast year traf- recommended number of lanes, is available fic should serve as a design control for geo- from the Division of Planning and must be ob- metric standards. tained by the designer before starting detailed design of new projects. 2.4.4 TRAFFIC DATA Normally, the ADT shown on the title sheet DOCUMENTATION for each project is actually the AADT. On The design traffic data to be shown on the some roads, such as those serving the beach title sheet of the plans are: areas, traffic is significantly heavier in one season. For these roads, the design should take • ADT Current − (current year specified), into consideration the ADT for the peak months. • ADT Projected − (future year specified), • DHV Projected − (year specified), 2.4.2 TRAFFIC COMPOSITION • Design Speed  mph [km/h], Vehicles of different sizes and weights • % Trucks − and, have different operating characteristics, which must be considered in highway design. Traffic • Direction of Distribution % − in predomi- composition is a measure of the proportion of nant direction. heavy trucks in the traffic stream, expressed as a percent of the DHV. All of the above information (except design speed) is obtained from the Division of Plan- Besides being heavier, large trucks gener- ning. In addition, the Division of Planning ally are slower and occupy more roadway provides current vehicle types and truck pat- space than passenger cars. The overall effect terns common to the project. The designer, of one truck on traffic operations is often based on criteria set forth in this manual and equivalent to several passenger cars. Traffic the Green Book, determines the design speed composition is an important factor in deter- for projects. mining a facility's ability to carry existing and future traffic volumes, geometrics, cross-

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2.4.5 HIGHWAY CAPACITY • Urban and industrialized areas usually have frequent access points creating The term “capacity” is used to express the roadside conflicts. These areas may need maximum hourly rate at which persons or ve- to be studied for their affect on highway hicles can reasonably be expected to traverse a capacity. point, such as a uniform section of a lane or a roadway, during a given time period under In the event one or more of these condi- prevailing roadway and traffic conditions. tions should occur, the designer should work with the Division of Planning and determine As part of the traffic data furnished by the its significance. Increasing capacity is not only Division of Planning, there will be a recom- costly but may be in conflict with the ap- mendation on the number of lanes to meet the proved scope of work and project intent. Any projected traffic demands. However, the de- attempt or request to analyze or justify this signer needs to be familiar with highway ca- type of change should receive approval prior pacity procedures and aware that as a project to expending any effort. is developed the original recommendation may need to be reevaluated. Reference is made to Two other key items to compare through- the TRB’s Highway Capacity Manual for out the design process, particularly at intersec- technical details and instructions for capacity tions, is the design-hour volume (DHV) versus analyses. Designers should be aware of several the service volume (selected design level of general conditions that may warrant a detailed service). If the service volume is not equal to capacity analysis: or greater than the expected design-hour vol- • Two-lane roadway sections that exceed ume capacity, problems can be expected and 1,400 passenger vehicles per hour (total other design alternatives need to be consid- two-way) should be investigated to see ered. if more lanes or other capacity improvements are necessary. 2.4.6 DESIGN VEHICLES • The capacity of a two-lane road is Where turning movements are involved, greatly reduced where there is limited the geometric design requirements are affected opportunity for passing slower-moving significantly by the types of vehicles using the vehicles. In terrain where it is facility. impracticable to provide adequate passing sight distance, additional lanes Four general classes of vehicles are or useable shoulder areas may be identified: (1) passenger cars, (2) buses, (3) required. trucks, and (4) recreational vehicles. The • The capacity of a two-lane road is passenger car class includes cars of all sizes, significantly affected by long, steep spot/utility vehicles, minivans, vans, and pick- grades with slow-moving trucks. An up trucks. Buses include inter-city (motor auxiliary climbing lane may be coaches), city transit, school, and articulated warranted. buses. The truck class includes single-unit trucks, truck tractor semi-trailer combinations, • The lack of shoulders affects vehicle and trucks or truck tractors with semi-trailers speeds indirectly leading to a decrease in in combination with full trailers. Recreational capacity. vehicles include motor homes, cars with • Intersection signalization and frequency camper trailers, cars with boat trailers, motor may change capacity requiring homes with boat trailers, and motor homes additional lanes. pulling cars. In addition, where provision is

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made for bicycles on a roadway, the bicycle should be avoided. It is better to consider av- should also be considered a design vehicle. erage terrain conditions over a longer length of road. Due to Delaware’s size, population dis- The specific design vehicles and their rela- tribution and predominant terrain, this manual tionships to geometric design are discussed in recognizes that many projects are more influ- detail in Chapter Seven-Intersections of this enced by the intensity of roadside develop- manual and Chapter 9 Intersections of the ment and associated activity than physical ter- Green Book. rain features.

2.5 OTHER DESIGN 2.5.2 FUNCTIONAL CLASSIFICATION CONTROLS Delaware has adopted a system of classify- Several other factors serve in various ways ing and grouping highways, roads and streets as controls for geometric design standards. as to their purpose and character of service they provide. These recognized functional classifications are shown in Figure 2-2. 2.5.1 TERRAIN CHARACTERISTICS Figure 2-2 Design standards used in flat areas may not Functional Classification be physically or economically practical in URBAN SYSTEM rugged terrain. Traditionally, most highway agencies recognize three categories of terrain Interstate characteristics−flat, rolling, and mountainous. Freeways and Expressways Because there are no areas that might be clas- Principal Arterial sified as mountainous in Delaware, the De- Minor Arterial partment has designated two categories of ter- Major Collector rain characteristics to be considered in relation Local to design standards. RURAL SYSTEM • Flat terrain. Any combination of gradients, length of grade, or horizontal Principal Arterial or vertical alignment that permits trucks Minor Arterial to maintain speeds that equal or Major Collector approach the speed of passenger cars. Minor collector Local • Rolling terrain. Any combination of gradients, length of grade, or horizontal In addition to those classifications shown in or vertical alignment that causes trucks Figure 2-2, there is a group of local streets to reduce their speeds substantially classified as “subdivision streets.” These are below that of passenger cars on some streets that lie within a DelDOT approved sections of the highway, but which does residential subdivision that have been deter- not involve sustained crawl speed by mined to be eligible for state maintenance. The trucks for any substantial distance. various facilities that comprise a designated functional system are shown on the official Designation of the terrain category in- DelDOT Functional Classification Map avail- volves considerable judgment rather than for- able from DelDOT’s Mapping Section. malized measurement and criteria. To assure consistency in design, the terrain category Urban and rural areas differ in land use should encompass road sections of at least 3 to density, the types of land use, density of street 6 miles (5 to 10 km). Frequent changes in ter- and roadway networks, access and mobility rain designation for short sections of road needs, multi-modal needs, and travel patterns.

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Because of these diverse needs, urban and ru- Expressways are similar to freeways but do ral functional systems are classified separately, allow limited access to intersecting state main- as shown in figure 2-2. Urban areas have tained roadways under strictly controlled con- populations of 5,000 or more. The boundaries ditions. They provide high speed, long- are set by the appropriate Metropolitan Plan- distance vehicular service. ning Organization (MPO) in cooperation with DelDOT. Urban areas are further classified Principal arterial roadways have the capac- into urbanized areas (population of 50,000 and ity for safely and efficiently carrying traffic over) and small urban areas (population be- flow at high speeds and high volumes for long tween 5,000 and 50,000). Rural areas fall out- distances. The travel patterns include inter- side the boundaries of urban areas. state, interregional, and intercity. Access and service to abutting properties is subordinate to providing through traffic movement. Opposing 2.5.2.1 ROADWAY TYPES WITHIN THE traffic streams are separated by a median, usu- CLASSIFICATION SYSTEM ally non-traversable in urban areas. At-grade The following discussion is a general de- intersections are permitted but are controlled scription of the classification of roadways. The both in location and design. Coordination and total highway system is functionally classified traffic progression are considered a major is- based on a hierarchy on how competing func- sue. tions of transportation movement and access are satisfied. Minor arterials have a capacity for medium to high speeds or medium to high volume traf- Interstates are a specially designated na- fic movements over medium to long distances tional system of highways serving most state safely and efficiently. The travel needs are re- capitols and major population centers for the gional, intercity, and intracity. Direct access to purpose of national defense and the safe and abutting land is subordinate to providing ser- efficient transportation of high traffic vol- vice to traffic movement. Intersecting high- umes. They are capable of serving larger vehi- ways, streets, or access to crossing movements cles carrying all types of goods with heavier are permitted but must meet spacing criteria, loads than permitted on lower class roadways. which allows signalization when volumes war- The design standards are significantly higher rant. Progression in providing signalization is in all areas, i.e. full control of access, in- desirable but may be difficult to achieve, par- creased pavement structure, increased lane ticularly in urban areas. widths, increased shoulder widths, wider me- dians, increased vertical clearances to all Major collectors have a capacity for mod- structures and increased strength requirements erate travel speeds and moderate traffic vol- for bridges, etc. Essentially interstate facilities umes for short travel distances providing for are to be strictly designed to the highest possi- intercity and intracity travel needs. Mobility ble standards. needs are balanced with direct access to pro- vide the desired service. Traffic progression Freeways are arterial highways with full may not be a major concern. control of access having the capacity for high speed and high volume traffic movements over Minor collectors are roadways that provide very long distances in an efficient and safe equal treatment and importance to abutting manner. The travel patterns are interstate, in- property access and the movement of traffic. terregional, or intercity. Opposing traffic They usually intersect with arterial roadways. movements are physically separated and ac- The progression of traffic is not considered a cess is only provided via grade separated in- major issue. terchanges at selected public roads.

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Local roads provide good access to adjoin- alignment or grade changes, resurfacing, and ing residences and businesses but limited op- minor traffic services improvements, such as portunity for through movement of traffic. traffic signals, curb and gutter, and channeli- Travel is short and movement is to intersecting zation. These projects may also include creat- roadways, usually of the collector classifica- ing opportunities for providing alternative tion. modes of travel (transit, bicycles, and pedes- trians). The proposed scope of work, available Because each classification reflects a par- funding and project needs, along with the ticular type of service, geometric design stan- many issues involved in context sensitive de- dards may vary, even for road sections within sign, must be evaluated in establishing the de- the same traffic volume group. These varia- sign standards. tions are considered in the tables of design standards in this manual. For design purposes Design standards appropriate for new con- the classifications of Principal and Minor Ar- struction or major reconstruction may be im- terials have been combined into one class (Ar- practical both economically and in the disrup- terials) and the Major and Minor Collectors tion of the social context of a community or have been combined as Collectors. The desig- project area. The goal is to strive to meet the nation of urban and rural arterials and collec- full geometric and cross sectional design con- tors has been maintained. trols in this manual and the Green Book for new construction and reconstruction projects. The designer should be aware that func- These two types of projects are generally de- tional classifications are not updated or re- scribed as follows: vised on an annual basis but more likely on a five to ten year frequency. When scoping a • New Construction. Projects on new project, particularly within the context sensi- alignment or major reconstruction pro- tive design environment, a project area could jects on existing alignment where sig- be considerably different than would be indi- nificant horizontal and vertical changes cated by its current designated functional clas- are included in the scope of work and sification. funded. • Reconstruction. Projects typically 2.5.3 MANUAL APPLICATION involving demolition and full depth replacement of the pavement structure, There are many types of projects requiring rubbilization or crack-and-seal of varying levels of design effort and selection of existing pavement combined with full design criteria. Most projects do not involve depth overlay, removal and replacement new alignment, new construction or major re- of any significant part of the construction that would allow significant substructure or superstructure, and the changes in grades and geometrics permitting total replacement of highway signs, the use of full (maximum and desirable) de- highway lighting, or drainage systems. sign standards as set forth in Green Book and Safety considerations are an important this manual. The majority of projects are part of reconstruction improvements. planned and designed to maintain the existing There is a third type of project. These highway system. Many projects are funded to projects are classified as Preventive address immediate needs such as interim im- Maintenance. Projects in this category are provement of the riding surface and improving defined as projects which include restoration or traffic services and safety. These projects may rehabilitation of specific elements of a highway include some or all of the following items: facility. These improvements are recommended widening, strengthening of pavement struc- as part of an acceptable pavement or bridge ture, flattening of slopes, minor isolated management system showing that such

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activities are a cost-effective means of 2.5.4 ACCESS CONTROL maintaining the bridge or pavement life. In general, any work that (1) retains pavement Access control is the regulation of public structural capacity (general overlays up to 2 ingress and egress to and from properties abut- inches or mill and replacement of portions of ting the highway facilities. Design standards the pavement structure up to 4 inches); (2) and their application are affected by a facil- prevents the intrusion of water into the ity’s designated level of access control. The pavement or pavement base (crack or joint four basic types of access control are: sealing, underdrains, restoration of drainage • Full Control of Access  Provides systems); (3) restores pavement rideability access to through-traffic lanes only at (profiling, milling); or (4) prevents deterioration selected public roads by means of of bridges (cleaning and painting, seismic ramps. Crossings at grade and direct retrofit, scour countermeasures, deck driveway connections are prohibited. rehabilitation and repair, deck drain cleaning) are considered to be work which extends the • Partial Control of Access  Gives service life of the highway. Please refer to the preference to through traffic movement current FHWA stewardship agreement. but provides some direct access connections with selected public roads, All projects on the National Highway Sys- either grade separated or at grade. tem (NHS), except preventive maintenance, • Access Management  Provides access must conform to the full standards, as set forth to land development while in AASHTO’s Green Book. When the mini- simultaneously preserving the flow on mum standards are not provided, a design ex- the surrounding road system in terms of ception must be prepared as provided in the safety, capacity, and speed. current Delaware Department of Transporta- tion/Federal Highway Administration Stew- • Conventional Highways  Permit ardship Agreement. access directly to abutting property within the guidelines and criteria Many projects include a review of safety established for the location, spacing and features and other roadway features. Fre- geometrics of the access points. Such quently project intent, funding, environmental guidelines are set forth in DelDOT’s concerns and other issues do not permit these Entrance Manual. projects to be designed in accordance with all the standards in the Green Book or this man- The functional classification system defines ual. However, each project should be initially a highway’s level of access in conjunction evaluated using the applicable standards. TRB with a facility’s purpose, importance, and Special Report 214, Designing Safer Roads: functional characteristics. The basic principles Practices for Resurfacing, Restoration, and in defining the level of access are: Rehabilitation provides a methodology for • Classify the road system by the pri- making decisions on which elements could be mary function of each roadway. addressed to be most cost-effective in improv- ing project safety. Flexibility both in applica- • Limit direct access to roads with higher tion of this manual and AASHTO allow the functional classifications. designer to select design standards that will • Locate traffic signals to emphasize provide a safer facility, meeting the project in- through traffic movements. tent, project funding, and user expectations. • Locate driveways and major entrances to minimize interference with traffic operations.

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• Use curbed medians and locate median sign is more fully discussed in Chapter Ten- openings to manage access movements Miscellaneous Design. and minimize conflicts. Controlling and managing access is accom- 2.5.6 BICYCLE FACILITIES plished through a combination of statutory au- thority, land-use ordinances, geometric design, Bicycle users are an important element and driveway regulations. when making decisions defining a project’s design parameters. Many existing streets and highway systems can accommodate bicyclists 2.5.5 PEDESTRIANS without significantly affecting costs or other impacts. Improvements that will enhance Pedestrians are an important part of the safety and promote increased bicycle use in- roadway environment. Pedestrian needs are clude: paved shoulders, wider outside traffic more prevalent and influential on design in ur- lanes, bicycle-safe drainage grates, adjusting ban areas but their needs in rural areas should manhole and utility covers, and maintaining a also be recognized. Pedestrian facilities in- smooth, clean riding surface. Bicycle facility clude sidewalks, traffic control features, ref- design details can be found in Chapter Ten- uge islands, curb cuts (depressed curbs and Miscellaneous Design and AASHTO’s Guide ramped sidewalks), and ramps for older walk- for the Development of Bicycle Facilities. ers and persons with mobility impairments. Pedestrian facilities are also an important sup- porting component for transit operations. 2.5.7 ECONOMICS

The typical pedestrian will not walk more Decisions on alignments, grades, widths, than 1 mile [1.5 km] to work or over 1/2 mile slopes and other items can greatly influence [1.0 km] to catch a bus. Pedestrian actions are the construction cost. Geometric and structural less predicable than those of the motorist. This standards higher than needed for a particular makes it difficult to design a facility for safe type of facility may cause increased expendi- and orderly movement of pedestrians. Pedes- tures that might be better spent on improving trians tend to walk in a path that represents the additional road sections. Use of standards that shortest distance between two points. Pedes- are too low may be uneconomical by contrib- trians tend to resist changes in grade or eleva- uting to early obsolescence of the facility. tion when crossing roadways and tend to avoid using special underpass or overpass pe- The standards established by the Depart- destrian facilities. ment reflect the best judgment as to design cri- teria for particular conditions. Sometimes the A pedestrian’s age has an important role in standards are expressed as minimum values how they use a facility. If the users are pre- but the opportunity often exists to use higher dominantly older, several measures have been than minimum standards without significant identified in the FHWA publications Highway additional costs. Designers should recognize Design Handbook for Older Drivers and Pe- these opportunities. At the same time they destrians and Guidelines and Recommenda- should recognize when increased costs for tions to Accommodate Older Drivers and Pe- higher standards cannot be justified. Designers destrians. Several of these design elements must continually be cost conscious within the are: keep the design simple, assume slower framework of established criteria, defined walking speeds, provide adequate median ref- scope of work, and project intent. uge islands at wide intersections, and assure the geometric design is compatible with en- hanced traffic control systems. Sidewalk de-

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2.5.8 SAFETY A significant factor contributing to safety is access to the facility. Reducing the number, Safety is a major control in roadway de- frequency, and variety of events to which a sign. Designs should minimize driver deci- driver must respond improves safety. All sions and reduce unexpected situations. De- roadways need to provide design features and signs should strive for uniformity in features operating characteristics that will reduce con- and traffic control. Driver safety involves a flicts and minimize the interference between variety of factors including: vehicles while still meeting the intended needs • The number and use (variety and fre- of the users. quency) of access points, Speed is often a contributing factor to • Operating speed, safety but its role must be related to the acci- • Type and width of median, dent site. The safest speed depends upon de- sign features, road conditions, traffic volumes, • Shoulder width, weather conditions, roadside use, spacing of intersecting roads, cross-traffic volumes, and • Alignment, other factors. Design features that reduce the • Grades, variance in speed of vehicles (such as flat grades, speed-change lanes, shoulders, grade • Roadside design (roadside slopes and separations, and appropriate signing and mark- unyielding obstacles), ings) improve highway safety. • The uniform and proper application of traffic control devices (signs, markings, In addition, it is important to recognize the and signals), and type and characteristics of the drivers expected to use the facility. Trip purpose directly relates • Properly designed intersections, par- to the mix of vehicles likely to use the road- ticularly in rural areas. way. Where trips are of one predominant type, i.e. commuter, recreational or commercial, the Established standards generally consider facility should be designed to fit this specific safety factors. Items such as minimum sight need. distances and limitations on minimum curva- ture for a particular design speed are generally The use of medians has been found to in- accepted as minimum fixed values. The safety crease safety on four-lane facilities. Depend- value of some other items, such as guardrail, ing upon the functional classification, funding shoulder widths, side slopes and lateral clear- and project scope, medians vary greatly in ances is not as clearly defined, and the de- width and treatment. signer may vary the treatment to suit the spe- cific needs and provide the maximum possible Even though improvements in alignment, safety where necessary. grade and traveled way cross section are in- cluded in the design, the roadside design itself It is difficult to completely separate safety is an important part of a safe design. Drivers and economic considerations. Designers leave the traveled way for a variety of reasons. should watch for opportunities to improve Most of these occurrences leave the driver safety in the design when little or no addi- without full control of the vehicle. This means tional cost is involved. At the same time, they that obstacles near the roadway as well as the should carefully evaluate proposed safety fea- physical cross section of the roadside become tures that may result in extremely high costs. potential contributors to safety. Roadside de- A well-documented study may be needed to sign is addressed in Chapter Ten- economically justify the potential safety bene- Miscellaneous Design and in greater detail in fits. AASHTO’s Roadside Design Guide.

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Another element in providing a safe design • The highway system, is the use of traffic control devices: signs, markings and signals. Driver expectation and • The year, month, hour of the day and reaction is very dependent upon the communi- day of the week, cations provided through traffic control de- • The accident report number, vices. Without a uniform, high-quality traffic control system even the best alignments and • The severity of the accident−fatality, roadway cross sections may not function in a injury or property damage, safe and efficient manner meeting user expec- • If alcohol or speed was involved, tations. The four basics of effective traffic control are: (1) design, (2) placement, (3) • The available light, weather and surface maintenance, and (4) uniformity. More detail conditions, on the design of traffic control devices is • The type of collision, if appropriate, found in Chapter 8-Traffic Services and the FHWA’s Manual on Uniform Traffic Control • The type(s) of vehicle(s) involved, Devices (MUTCD). • The type of traffic control and if it was functioning, and A major element in providing a safe design in rural areas is at-grade intersections. Safety • The primary contributing circumstances. can be improved by channelizing intersec- tions, providing adequate sight distance (in- Road Study Listings are compiled each cluding stopping, decision, and intersection year for all the accidents occurring during the sight distance), proper lighting, signing and year. Designers can request accident reports traffic control devices and, where necessary, from the accident Data Coordinator in Plan- providing for pedestrians (refuge islands and ning. sidewalks). Intersections are an important de- sign element and are discussed in detail in The codes for the accidents are revised pe- Chapter Seven-Intersections of this manual riodically and the data from Road Study List- and Chapter 9 Intersections in the Green ings for prior years may vary somewhat from Book. that currently provided. Designers should ob- tain copies of both the current accident coding One or more of the factors that have been sheets and those used earlier to accurately in- discussed may be applicable to a project. The terpret the data. designer should carefully review accident re- cords and studies of the location as a guide to Designers should also refer to the current identifying locations where some form of Traffic Summary from Traffic to determine the safety improvement may be needed. milepost locations for each road in order to reference accident locations to design projects. Statistical records for accidents involving injuries or fatalities are compiled for each road The Critical Rate Ratio Report, prepared by in the state through the Highway Safety im- Traffic, shows the accident statistics by seg- provement Program (HSIP) administered by ment for each road. Designers should review the Traffic section. For each accident the Road this report to identify any areas with high ac- Study Listing includes valuable design infor- cident rates within the road section being de- mation such as: signed and consider improvements within the design scope to reduce accident frequencies. • Milepost location, • Intersecting roads, if any, • The county, city, town or area,

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2.5.9 ENVIRONMENT as project designs are developed, scoping meetings are held, and public involvement Each project receives a level of evaluation continues, other important issues will very as to its impact on environmental issues as es- likely arise. tablished by state and national goals as well as its affect on community and area values. Pro- jects on new alignment receive the most in- As a part of a project’s development proc- tense and detailed evaluation. ess, the designer will receive one or more of the following types of environmental docu- ments. These are: (1) SEE (Social, Economic As a part of the evaluation at the initial and Environmental) Report, (2) Categorical planning and funding stages, projects are clas- Exclusion (CE), (3) Environmental Assess- sified according to their probable impact on ment (EA), (4) Finding of No Significant Im- the environment and the level of expected im- pact (FONSI), (5) Draft Environmental Impact pact on any affected communities and the pro- Statement (DEIS), (6) Final Environmental ject area. These two elements determine the Impact Statement (FEIS) or a Record of Deci- type of environmental studies and public in- sion (ROD). The level of environmental as- volvement to be conducted on a project. Pro- sessment given to a project is a major consid- jects reaching the design phase have been eration in establishing its design controls and through some level of environmental studies standards since commitments made in these with many of the important design issues iden- assessments must be fully incorporated in the tified. However, it should be recognized that design.

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