2-20 A Policy on Geometric Design of Highways and Streets during certain hours of the day. However, because of the delays caused by other traffic during peak hours, such schedules generally are made to avoid these hours. For design of a particular roadway, data on traffic composition should be determined by traffic studies. Truck traffic should be expressed as a percentage of total traffic during the design hour (in the case of a two-lane highway, as a percentage of total two-way traffic, and in the case of a multilane highway, as a percentage of total traffic in the peak direction of travel). --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- In urban areas, traffic composition is generally more complex, with the presence of pedestrians, bicyclists, and transit vehicles, in addition to passenger cars and trucks. Designers should develop designs for each facility that strike an appropriate balance among all transportation modes served by the facility considering the functional classification and context of the facility, the volumes to be served for each mode, and the area plan for accommodating each mode. Additional discussion of achieving a balance among transportation modes on urban area facilities is found in Chapter 1. Specific information about effective design to serve pedestrians, bicycles and transit, respectively, may be found in the AASHTO Guide for the Planning, Design, and Operation of Pedestrian Facilities (2), the AASHTO Guide for the Development of Bicycle Facilities (7), and the AASHTO Guide for Geometric Design of Transit Facilities on Highways and Streets (8). Under interrupted-flow conditions in urban areas, the criteria for determining traffic composition differ from those used elsewhere. At important intersections, the percentage of trucks during the morning and evening peak hours should be determined separately. Variations in truck traffic between the various traffic movements at intersections may be substantial and may influence the appropriate geometric layout. The percentage of trucks may also vary considerably during a particular hour of the day. Therefore, it is advisable to count trucks for the several peak hours that are considered representative of the 30th highest or design hour. A convenient value that appears to be appropriate for design use is the average of the percentages of truck traffic for a number of weekly peak hours. For highway-capacity analysis purposes, local city-transit buses should be considered separately from other trucks and buses. 2.3.5 Projection of Future Traffic Demands Geometric design of new roadways or improvements to existing roadways should not usually be based on current traffic volumes alone, but should consider future traffic volumes expected to use the facility. However, traffic forecasting is not an exact science, and involves many assumptions about development patterns, changes in travel behavior, and technology. To better account for the inherent uncertainties involving traffic forecasts, a designer may consider using a rangebased traffic forecast that has lower and upper bounds. A design may be evaluated for these different traffic volume scenarios to characterize its sensitivity to the differences in the forecasts. Even if the design does not change, the designer will have a better understanding of how the facility may operate in the future. Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. Design Controls and Criteria It is difficult to define the life of a roadway because major segments may have different lengths of physical life. Each segment is subject to variations in estimated life expectancy for reasons not readily subject to analysis, such as obsolescence or unexpected radical changes in land use, with the resulting changes in traffic volumes, patterns, and demands. Right-of-way and grading may be considered to have a physical life expectancy of 100 years; minor drainage structures and base courses, 50 years; bridges, 25 to 100 years; resurfacing, 10 years; and pavement structure, 20 to 30 years, assuming adequate maintenance and no allowance for obsolescence. Bridge life may vary depending on the cumulative frequency of heavy loads. Pavement life can vary widely, depending largely on initial expenditures and the repetition of heavy axle loads. The assumption of no allowance for functional obsolescence is open to serious debate. The principal causes of obsolescence are increases in the number of intersections and driveways and increases in traffic demand beyond the design capacity. On non-freeway roadways, obsolescence due to addition of intersections and driveways is much more difficult to forestall; this occurs particularly in urban and suburban areas, but may occur in rural areas as well. In a practical sense, the design volume should be a value that can be estimated with reasonable accuracy. Many designers believe the maximum design period is in the range of 15 to 24 years. Therefore, a period of 20 years is widely used as a basis for design. Traffic cannot usually be forecast accurately beyond this period on a specific facility because of probable changes in the general regional economy, population, and land development along the roadway, which cannot be predicted with any degree of assurance. 2.3.6 Speed Speed is one of the most important factors considered by travelers in selecting alternative routes or transportation modes. Travelers assess the value of a transportation facility in moving people and goods by its reliability, convenience, and economy, which are generally related to its speed. The attractiveness of a public transportation system or a new roadway are each weighed by the travelers in terms of time, convenience, and money saved. Hence, the desirability of rapid transit may well rest with how rapid it actually is. In addition to driver and vehicle capabilities, the speed of vehicles on a road depends on five general conditions: yy physical characteristics of the roadway, yy amount of roadside interference, yy weather, yy presence of other vehicles, and yy speed limitations (established either by law or by traffic control devices). Although any one of these factors may govern travel speed, the actual travel speed on a facility usually reflects a combination of these factors. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. 2-21 2-22 A Policy on Geometric Design of Highways and Streets There are important differences between design criteria applicable to low- and high-speed designs. To implement these differences, the upper limit for low-speed design is 45 mph [70 km/h] and the lower limit for high-speed design is 50 mph [80 km/h]. 2.3.6.1 Operating Speed Operating speed is the speed at which drivers are observed operating their vehicles during freeflow conditions. The 85th percentile of the distribution of observed speeds is the most frequently used measure of the operating speed associated with a particular location or geometric feature. The following geometric design and traffic demand features may have direct impacts on operating speed: yy horizontal curve radius, yy grade, yy access density, yy median treatments, yy on-street parking, yy signal density, yy vehicular traffic volume, and yy pedestrian and bicycle activity. 2.3.6.2 Running Speed The speed at which an individual vehicle travels over a highway section is known as its running speed. The running speed is the length of the highway section divided by the time for a typical vehicle to travel through the section. For extended sections of roadway that include multiple roadway types, the average running speed for all vehicles is the most appropriate speed measure for evaluating level of service and road user costs. The average running speed is the sum of the distances traveled by vehicles on a highway section during a specified time period divided by the sum of their travel times. Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- The objective in design of any engineered facility used by the public is to satisfy the public’s demand for service in an economical manner, with efficient traffic operations and with low crash frequency and severity. The facility should, therefore, accommodate nearly all demands with reasonable adequacy and also should only fail under severe or extreme traffic demands. Because only a small percentage of drivers travel at extremely high speed, it is not economically practical to design for them. They can use the roadway, of course, but will be constrained to travel at speeds less than they consider desirable. On the other hand, the speed chosen for design should not be that used by drivers under unfavorable conditions, such as inclement weather, because the roadway would then be inefficient, might result in additional crashes under favorable conditions, and would not satisfy reasonable public expectations for the facility. Design Controls and Criteria 2-23 One means of estimating the average running speed for an existing facility where flow is not interrupted by signals or other traffic control devices is to measure the spot speed at one or more locations. The average spot speed is the arithmetic mean of the speeds of all traffic as measured at a specified point on the roadway. For short sections of roadway, on which speeds do not vary materially, the average spot speed at one location may be considered an approximation of the average running speed. On longer stretches of rural highway, average spot speeds measured at several points, where each point represents the speed characteristics of a selected segment of roadway, may be averaged (taking relative lengths of the roadway segments into account) to provide a better approximation of the average running speed. The average running speed on a given roadway varies during the day, depending primarily on the traffic volume. Therefore, when reference is made to a running speed, it should be clearly stated whether this speed represents peak hours, off-peak hours, or an average for the day. Peak and off-peak running speeds are used in design and operation; average running speeds for an entire day are used in economic analyses. The effect of traffic volume on average running speed can be determined using the procedures of the Highway Capacity Manual (HCM) (43). The HCM shows the following: yy Freeways and multilane highways in rural areas—there is a substantial range of traffic volumes over which speed is relatively insensitive to the volume; this range extends to fairly high volumes. Then, as the volume per lane approaches capacity, speed decreases substantially with increasing volume. yy Two-lane highways—speed decreases linearly with increasing traffic volume over the entire range of volumes between zero and capacity. yy Streets in urban areas—speed decreases with increasing traffic volume over the entire range of volumes between zero and capacity; the decrease in speed with increasing volume is nonlinear at higher volumes. Design speed is a selected speed used to determine the various geometric design features of the roadway. The selected design speed should be a logical one with respect to the anticipated operating speed, topography, the adjacent land use, modal mix, and the functional classification of the roadway. In selection of design speed, every effort should be made to attain a desired combination of safety, mobility, and efficiency within the constraints of environmental quality, economics, aesthetics, and social or political impacts. Once the design speed is selected, all of the pertinent roadway features should be related to it to obtain a balanced design. On lower-speed facilities, use of above-minimum design criteria may encourage travel at speeds higher than the design speed. Some design features, such as curvature, superelevation, and sight distance, are directly related to, and vary appreciably with, design speed. Other features, such as widths of lanes and shoulders and clearances to walls and rails, are not directly related to design speed but Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- 2.3.6.3 Design Speed 2-24 A Policy on Geometric Design of Highways and Streets they do affect vehicle speeds. Thus, when a change is made to design speed, many elements of the roadway design will change accordingly. The selected design speed should be consistent with the speeds that drivers are likely to travel on a given roadway. Where a reason for limiting speed is obvious, drivers are more apt to accept lower speed operation than where there is no apparent reason. A roadway of higher functional classification may justify a higher design speed than a lesser classified facility in similar topography. A low design speed, however, should not be selected where the topography is such that drivers are likely to travel at high speeds. Drivers do not adjust their speeds to the importance of the roadway, but to their perception of the physical limitations of the highway and its traffic. Lower speeds are desirable for thoroughfares in walkable, mixed-use urban areas and this desire for lower speeds should influence the selection of the design speed. For design of such streets, a target speed should be selected (29). The target speed is the highest speed at which vehicles should operate on a thoroughfare in a specific context, consistent with the level of multimodal activity generated by adjacent land uses, to provide both mobility for motor vehicles and a desirable environment for pedestrians, bicyclists, and public transit users. The target speed is intended to be used as the posted speed limit. In some jurisdictions, the speed limit is established based on measured speeds. In these cases, it is important for the design of the thoroughfare to encourage an actual operating speed that equals the target speed (16, 35). The selected design speed should reflect the needs of all transportation modes expected to use a particular facility. Where traffic and roadway conditions are such that drivers can travel at their desired speed, there is always a wide range in the speeds at which various individuals will choose to operate their vehicles. A cumulative distribution of free-flow vehicle speeds typically has an S-shape when plotted as the percentage of vehicles versus observed speed. The selected design speed should be a high-percentile value in this speed distribution curve (i.e., inclusive of nearly all of the desired speeds of drivers, wherever practical). It is desirable that the running speed of a large proportion of drivers be lower than the design speed. Experience indicates that deviations from this desired goal are most evident on sharper horizontal curves. In particular, curves with low design speeds (relative to driver expectation) are frequently overdriven and may have higher crash frequencies. Therefore, it is important that the design speed used for horizontal curve design be a conservative reflection of the expected speed on the constructed facility. Table 2-1 shows the corresponding design speeds in metric and U.S. customary units in 5-mph [10 km/h] increments. This table should be used in converting the units of measurement of design speeds. Although the selected design speed establishes the limiting values of curve radius and minimum sight distance that should be used in design, there should be no restriction on the use of flatter --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. Design Controls and Criteria horizontal curves or greater sight distances where such improvements can be provided as part of an economical design. Even in rugged terrain, an occasional tangent or flat curve may be desirable. Isolated features designed for higher speeds may not encourage drivers to speed up, although a succession of such features might. In such cases, the entire section of highway should be designed for a higher speed. A substantial length of tangent between sections of curved alignment is also likely to encourage high-speed operation. In such situations, a higher design speed should be selected for all geometric features, particularly sight distance on crest vertical curves and across the inside of horizontal curves. Table 2-1. Corresponding Design Speeds in Metric and U.S. Customary Units --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- U.S. Customary Metric Corresponding Design Speed (mph) Design Speed (km/h) 15 20 20 30 25 40 30 50 40 60 45 70 50 80 55 90 60 100 70 110 75 120 80 130 85 140 A pertinent consideration in selecting design speeds is the average trip length. The longer the trip, the greater is the driver’s desire to use higher speeds. Therefore, as the average trip length served by a facility increases, higher functional classes of roads with higher design speeds are more appropriate. In the design of a substantial length of highway, it is desirable to select a uniform design speed. However, changes in terrain and other physical controls may dictate a change in design speed on certain sections. If so, the introduction of a lower design speed should not be done abruptly but should be effected over sufficient distance to permit drivers to gradually change speed before reaching the highway section with the lower design speed. Where it is appropriate to reduce horizontal and vertical alignment features, many drivers may not perceive the lower speed condition ahead, and therefore, it is important that they be warned well in advance. The changing condition should be indicated by such controls as speed-zone and curve-speed signs. Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. 2-25 2-26 A Policy on Geometric Design of Highways and Streets On highways in rural areas and on high-type facilities in urban areas, a percentage of vehicles is usually able to travel at near the free-flow speed governed by geometric design elements; therefore, the selection of an appropriate design speed is particularly important. However, in many arterial streets, vehicle speeds during several hours of the day are limited or regulated more by the presence of large volumes of vehicles and by traffic control devices, rather than by the physical characteristics of the street. In such cases, the selection of a design speed is less critical to efficient operation and low crash frequencies and severities. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- During periods of low-to-moderate volume, speeds on arterial streets are governed by such factors as posted speed limits, midblock turns into and out of driveways, intersectional turns, traffic signal spacing, and signal timing for progression. When arterial street improvements are being planned, factors such as future posted speed limits, physical and economic constraints, and running speeds likely to be attained during off-peak hours should be considered. All of these factors should influence the selection of an appropriate design speed. Horizontal alignment generally is not the governing factor in restricting speeds on arterial streets. Proposed improvements generally are patterned to the existing street system, and minor horizontal alignment changes are commonly made at intersections. The effect of these alignment changes is usually small because operation through the intersection is regulated by the type of traffic controls needed to handle the volume of cross and turning traffic. Superelevation may be provided at curves on arterial streets in urban areas, but the amount of superelevation needed is determined in a different manner than for open-road conditions in rural areas. Wide pavement areas, proximity of adjacent development, control of cross slope and profile for drainage, and the frequency of cross streets and entrances all contribute to the need for lower superelevation rates on arterial streets in urban areas. The width of lanes, offset to curbs, proximity of poles and trees to the traveled way, presence of pedestrians within the right-of-way, and nearness of business or residential buildings, individually or in combination, often affects speeds. Section 3.3.6 provides guidance on horizontal alignment design for low-speed conditions in urban areas. Topography can materially affect the choice of design speed on arterial streets. Many cities were developed along watercourses and include areas varying from gently rolling to mountainous terrain. Streets may have been constructed originally with only minor grading to fit the topography. Because an arterial street is usually developed to fit the alignment of an existing street, both through business and residential areas, it generally follows a varying vertical profile. Once the design speed is selected, appropriate sight distance should be provided at all crests and across the inside of horizontal curves. Profiles with long, continuous grades should be designed with proper consideration for the speeds of mass transit and commercial vehicles. Extra lanes on the upgrades may be needed so that the grade can match other portions of the facility in capacity and enable vehicles that can proceed at a reasonable speed to pass slower moving vehicles. Arterial streets in urban areas should be designed and control devices regulated, where practical, to permit running speeds of 20 to 45 mph [30 to 75 km/h]. Speeds in the lower portion of this Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. Design Controls and Criteria range are applicable to local and collector streets through residential areas and to arterial streets through more crowded business areas, while the speeds in the higher portion of the range apply to high-type arterials in outlying suburban areas. For arterial streets through crowded business areas, coordinated signal control through successive intersections is generally needed to permit attainment of even the lower speeds. Many cities have substantial lengths of signal-controlled streets that operate at speeds of 15 to 25 mph [20 to 40 km/h]. Chapters 5 through 8 of this policy provide further guidance on appropriate design speeds for specific roadway types. 2.3.7 Traffic Flow Relationships Traffic flow conditions on roadways can be characterized by the volume flow rate expressed in vehicles per hour, the average speed in miles per hour [kilometers per hour], and the traffic density in vehicles per mile [vehicles per kilometer]. These three variables—volume, speed, and density—are interrelated and have predictable relationships. The generalized relationships between volume, speed, and density for uninterrupted flow facilities, as presented in the HCM (43) are shown in Figure 2-4. The relationships shown in Figure 2-4 are conceptual in nature and do not necessarily correspond to the actual relationships used in specific HCM procedures. For example, the HCM procedures for freeways and multilane highways show that speed does not vary with volume through most of the low and intermediate volume range, as shown in Figure 2-4. The HCM procedures for two-lane highways show that speed varies linearly with volume throughout the entire volume range from zero to capacity. Density, the number of vehicles per unit length of roadway, increases as vehicles crowd closer together. As Figure 2-4 shows, when speeds decrease, increased crowding can occur and drivers can comfortably follow more closely behind other vehicles. Density is used in the HCM as the measure of quality of traffic service for freeways and multilane highways. Traffic volumes also vary with density from zero to maximum flow rate, as shown in Figure 2-4. The two points of zero flow in Figure 2-4 represent either no vehicles at all or so many vehicles on the roadway that flow has stopped. The maximum flow is reached at the point of maximum density. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- Interference to traffic flow causes speeds to be reduced, vehicles to travel closer together, and density to increase. Interference may be caused by weather conditions, cross traffic, disabled vehicles, crashes, or other conditions. As these conditions cause more interference, the flow rates within certain limits can still be maintained but with reduced speed, closer vehicle spacing, and greater density. When interference becomes so great (despite closer vehicle spacing and greater density) that the average speed drops below that needed to maintain stable flow, there is a rapid decrease in speed and traffic flow, and severe congestion occurs. Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. 2-27 2-28 A Policy on Geometric Design of Highways and Streets Sf Speed (mph) Speed (mph) Sf So Do So Dj Do 0 Dj Flow (veh/h/in.) Density (veh/mi/in.) 0 Flow (veh/h/in.) Legend o Vm Do Vm Vm Do = = Dj So Sf = = = Oversaturated flow Maximum flow Optimum density (sometimes called critical density) Jam density Optimum speed (often called critical speed) Theoretical speed selected by the first driver entering a facility (i.e., under zero density and zero flow rate conditions) Dj Density (veh/mi/in.) Figure 2-4. Generalized Speed-Volume-Density Relationships (43) When traffic on a highway encounters interference that limits or reduces the roadway capacity in a single area, the result is a “bottleneck.” If the flow entering this bottleneck does not exceed its capacity, flow remains stable and no significant congestion should occur. However, when the upstream section carries more vehicles than the bottleneck can accommodate, a breakdown in traffic flow results. Speeds are reduced to a crawl and vehicles begin to queue upstream until incoming flow again falls below the outflow capacity. To avoid bottleneck situations, care should be taken to design roadways with consistent volume-carrying capacity. The level-of-service concept discussed in Section 2.4.5 helps in obtaining this consistency. An intersection is often an unavoidable bottleneck. This reduction in capacity becomes acute when the intersection is controlled by stop signs or traffic signals. At a traffic signal, vehicles that arrive during the red phase encounter a zero-capacity bottleneck. These vehicles form a queue until the green phase begins, removing the restraint, and discharging the queue. If the incoming volume is too high, not all vehicles in the queue can be discharged during the green phase, and there is a continuing buildup of the queue. Arrivals at the intersection are generally predictable in urban areas where the approaching vehicles are platooned by upstream signals. In the suburban or rural contexts, vehicle arrivals are Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- 0 Design Controls and Criteria 2-29 often random. This random arrival pattern should be recognized in the design of appropriate cycle times, turn-lane storage lengths, and approach capacity. At bottlenecks where traffic slows down or stops, each vehicle and its occupants incur delay. Delays increase fuel consumption and air pollution, which create undesirable economic and environmental effects. 2.4 HIGHWAY CAPACITY 2.4.1 General Characteristics The term “capacity” is used to express the maximum hourly rate at which persons or vehicles can reasonably be expected to traverse a point (i.e., a uniform section of a lane or a roadway) during a given time period under prevailing roadway and traffic conditions. The range of traffic flow on a highway can vary from very light volumes to volumes that equal the capacity of the facility as defined above. In the generic sense, the term also encompasses broader relations between highway characteristics and conditions, traffic composition and flow patterns, and the relative degree of congestion at various traffic volumes. Highway capacity issues in this broad sense are discussed below. Sections 2.4.2 through 2.4.6 provide a brief overview of the principles and major factors concerning roadway design capacity. To determine the capacity for a particular roadway design, the designer should refer to the Highway Capacity Manual (HCM) (43) for guidance. The HCM is used as the basic reference for the following discussion, but other tools are available for performing operational analysis and these may be more appropriate depending on the circumstances. The HCM includes procedures for analyzing the level of service for all modes of travel—pedestrian, bicycle, transit, and motorized vehicles (43). 2.4.2 Application Roadway capacity analysis serves three general purposes, including: yy Roadway design—A knowledge of roadway capacity is essential to properly fit a planned roadway to traffic demands. Roadway capacity analysis is used both to select the roadway type and to determine dimensions such as the number and types of lanes and the minimum lengths for weaving sections. Copyright American Association of State Highway and Transportation Officials Provided by IHS Markit under license with AASHTO No reproduction or networking permitted without license from IHS © 2018 by the American Association of State Highway and Officials. Licensee=Arkansas StateTransportation Highway & Transportation Dept/5988317001, User=Sichmelle Resale, 10/09/2018 09:17:18 MDT All rights reserved. Duplication Not is aforviolation of applicable law. --`,```,``,`,`,`,``````,,,,``-`-`,,`,,`,`,,`--- yy Transportation planning studies—Roadway capacity analysis is used in these studies to assess the adequacy or sufficiency of existing roadway networks to service current traffic. In addition, it is used to estimate the time in the future when traffic growth may exceed the capacity of a roadway or perhaps reach a level of congestion below capacity that is considered undesirable.
