INTRODUCTION

1. INTRODUCTION This chapter presents guidance on the application of geometric design criteria to facilities functionally classified as rural and urban arterials. Rural and urban arterials provide a high-speed, high volume network for travel between major points in both rural and urban areas. This chapter discusses two types of roadways: Rural Arterials and Urban Arterials.

2. RURAL ARTERIALS Rural arterials constitute an important part of the rural highway system. They consist of Interstate system and most rural freeway, multilane roadways, and two-lane highways connecting urban centers. Design Speed 60 – 120 km/h depending on terrain, driver expectancy, and the alignment of existing facility in the case of reconstruction projects 100-120 km/h level 80-100 km/h rolling 60-80 km/h mountainous terrain Design Traffic Volume Current ADT -> Projected ADT in 20 years later Projected ADT -> DHV using K = 0.15

3. RURAL ARTERIALS Level of Service For acceptable degrees of congestion, rural arterials and their auxiliary facilities should generally be designed for LOS B, except in mountainous areas where LOS C is acceptable. Sight Distance see Exhibit 7-1 for SSD and PSD intersections and railroad crossings should be grade separated or provided with adequate sight distance. Intersection should be placed in sag and /or tangent locations, where practical to allow max. visibility. Alignment A smooth flowing alignment is desirable on a rural arterial. Grades The length and steepness of grades directly affect the operational characteristics of an arterial. See Exhibit 7-2 for max. grade

4. RURAL ARTERIALS Number of lanes Lanes = f(volume, LOS, capacity) Superelevation Superelevation should be considered on curves. Emax = 12 and emax = 8% for ice and snow regions Cross Slope Two-lane rural roadways are normally designed with a centerline crown and cross slopes ranging from 1.5 to 2% with the higher values being most prevalent. Multilane roadways are crowned at the centerline or sloped in one direction. Vertical 4.9 m for new or reconstructed structures Clearances 4.3 for existing structures if allowed by local statute. Structures Full width for the approach roadways should normally provided across all new bridges. A width at least equal to the width of the TW + 0.6 m clearance is placed on each side of existing bridges to remain in place.

5. RURAL ARTERIALS Traffic Control Signs, pavement delineation, pavement markings follow Devices MUTCD Width Logical approach to determining appropriate lane and shoulder widths is to provide a width related to the traffic demand. See Exhibit 7-3 for min. width of traveled way and Usable shoulder. Horizontal A clear unobstructed roadside is highly desirable. Clearance to Refer Roadside Design Guide for proper treatment for Obstructions fixed objects or non-traversable slopes fall within the clear roadside zones. Cross Section cross section should be designed for better drainage ROW ROW should be acquired to adequately provide the widerroadway section.

6. RURAL ARTERIALS Provision for The alignment and profile should provide sections for safe Passing passing at frequent intervals in designing two-lane, two way arterials. When achieving sufficient PSD is not pratcical, auxiliary lanes such as truck climbing lanes or passing lanes should be considered. Four-Lane four-lane divided arterials are the ultimate development Divided that meets the future traffic demand. A phase plan from Arterials two-lane two way arterial to four-lane two way arterial is preferred. see Exhibit 7-5 for the conversion from two-lane to four lane arterials

7. RURAL ARTERIALS Multilane A multilane undivided arterial is the narrowest arterial Undivided on which each traffic lane is intended to be used by traffic Arterials in one direction of travel. Divided A divided arterial is one with separated lanes for traffic Arterials in opposite directions. It may be on a single roadbed or two separated roadways. Lane Widths 3.6 m Cross Slope Each roadway of a divided arterial may be sloped to drain to both edges or each roadway m,ay be sloped to drain to its outer edge. Slope 1.5 – 2% Shoulder 2.4 m for outside usable shoulder width 1.2 m for inside usable shoulder width Median Barrier Clearance see AASHTO Roadside Design Guide

8. RURAL ARTERIALS Divided Arterials Medians on highways without at grade intersections, the median may be as narrow as 1.2-1.8 m. Medians 3.5 m to 9 m wide provide protection for left- turning vehicles at intersections. The median width at rural un-signalized intersections is at least 7.5 m. Median width of > 18 m are undesirable at intersections that are signalized or may need signalization in the foreseeable future. Alignment and Profile A divided arterial consists of two separated roadways or alignments. Profile design is much easier that that for multilane highways.

9. RURAL ARTERIALS Divided Arterials Climbing Lanes Climbing lanes generally are not as easily justified on on Multilane multilane as on two-lane arterials. Arterials SuperelevatedA divided arterial on a curve should be superelevated Cross Sectionsto ensure safe traffic operations, pleasing appearance, and economy. See Exhibit 7-6 for SE and Exhibit 7-7. Case I: Whole Traveled Way including Median as a plane section. Median Width  4.5 Case II: Median is held in a horizontal plane and two traveled ways are rotated separated around their median edge for median 4-18m wide. Case III:Two TWs are treated separately for SE with a resulting variable difference in elevation at the median edges for median > 18 m.

10. RURAL ARTERIALS Divided Arterials Cross Sections Cross Section elements include widths/details of TW, ROW Width shoulders, medians, sideslopes, clear zones, drainage channels. See Exhibit 7-8 and 7-9. Sections with Widely It is practical to separate the one-way roadways of a Separated Roadwaysdivided arterial. In doing so, intersections between a crossroad and a one-way roadway are greatly simplified in design and operation. Intersections High type intersections and interchanges are highly considered on arterials that do not have full control of access. Adequate turning widths with accel and decel tapers will provide a minimum design. Access Management Access Control is the important factor for the design of arterials.

11. RURAL ARTERIALS Divided Arterials Bikeways and Rural arterials often provide the only direct connection Pedestrian Facilities between populated areas and locations to which the public whishes to travel. Bike and peds also wish to travel the same destination pints. Care should be taken to the provision of the facilities for bike and ped travel. Bus Turnouts Bus turnouts can be located on a rural arterial.

12. URBAN ARTERIALS Urban Arterials carry large traffic volumes within and through urban areas.Design varies from freeways to two-lane streets. There are two two classes of urban arterials: principal and minor. This chapter considers all urban streets and leaves freeways in Chapter 8. Design Speed50 – 100 km/h. Lower speed in CBD and more developed areas. Higher speeds in suburban and developing areas. Design Traffic 20 years from the date of construction completion Volume LOS C for rural and suburban arterials and their auxiliary facilities ; D for heavily developed areas. Sight DistanceExhibit 7-1 for SSD and PSD. Alignment Best alignment design possible since an urban arterial involves many constraints.

13. URBAN ARTERIALS Gradessee Exhibit 7-10. Superelevation Curves on low speed curbed arterial streets are often not superelevated. When superelevation is considered, Case II distribution discussed in Chapter 3 should be used. Cross Slope 1.5 – 3% Vertical Clearance4.9 m for new and reconstruction projects. 4.3 m for existing structures kept in place. Lane Widths 3.0 –3.6 m. 3.3 m should be used quite often for urban arterial street designs. 3.6 m is ideal for urban streets. Curbs and A measure of safety to the occasional peds in sparsely Shoulders developed areas and provide space for bike users where allowed by law.

14. URBAN ARTERIALS Number of LanesCapacity analysis needed to estimate number of lanes. Roadway Width Accommodate through and turning traffic lanes, medians, curbs, appropriate clearances from curb or barrier faces. Medians Medians are a desirable feature of arterial streets and should be provided where space permits. A median of 1.2 m is better than none. 5.4 m is better to accommodate left-turn movements. See Exhibit 7-8 Median openings on divided highways with depressed or raised curbed medians should be carefully considered. Such openings should be only provided for street intersections or for major development. Two-Way Left Turn Lane (TWLTL ) for a street with an odd number of lanes and at the speed of 40-70 km/h and no heavy left-turns

15. URBAN ARTERIALS DrainageAn adequate drainage system to accommodate design runoff should be included in the design of urban arterials. It includes the design of location of inlets, curbs, and others. Parking Lanes 3.0 –3.6 m. Parking turnouts could be considered for areas in downtown districts and and for areas with large office or industrial complex. Borders and The border area should include a sidewalk and a Sidewalks buffer between the sidewalk and the curb. Min. 2.4 – 3.6 m for the border width. See Exhibit 7-13 and 7-14. Roadway Width for The min. clearance width for new bridges on arterial Bridges streets should be the same as curb-to-curb width of the street.

16. URBAN ARTERIALS Hor. Clearance Clear roadside design is recommended for urban To Obstructions arterials whenever practical. 0.5 m between curb face and object 1.0 m near turning radii at intersections and driveways. ROW Width covers all the cross section elements including through TW, medians, auxiliary lanes, shoulders, borders, and possibly, frontage roads, roadside clear zones, side slope, drainage facilities, utility appurtenances, and retaining walls.

17. URBAN ARTERIALS Access Management Partial control of access and the application of access management techniques are highly desirable ion an urban or suburban arterial.Access control and access management may be exercised by statute or through application of zoning ordinates, driveway regulations, turning and parking regulations, and effective geometric highway design. Control by Statute When statutory control is applied to an arterial street, access is usually limited to the cross streets or to other major traffic generators. Control by Zoning Zoning can be used effectively to control the type of property development along an arterial and thereby influence the type and volume of traffic generated. For example, Off-Street parking, parking distant from the arterial street, connection to the arterial street through a cross road.

18. URBAN ARTERIALS Access Management Control by Driveway Driveway control can be effective in Regulations preserving the function of arterial streets. Control by Geometric Right-Turn in and right-turn out. Design left-turn in and out, frontage roads

19. URBAN ARTERIALS Pedestrian Facilities The design of urban arterials should consider sidewalks, crosswalks, and sometimes grade separations for pedestrians. Sidewalks should be constructed initially along all arterial streets that are not provided with shoulders, even through pedestrian traffic may be light. The use of crosswalks at typical curbed street intersections may be difficult for persons with disabilities. Curb ramps of appropriate width and slope must be provided in curbed areas that have sidewalks.

20. URBAN ARTERIALS Traffic Control Measures Traffic Control Devices: traffic signals and signal spacing Regulatory Measures: Restrictions to turning movements and prohibition of curbside parking, stopping, or standing Directional Lane Usage: Reversible lane operation is sometime used to improve operational efficiency of arterial streets. One way operations in urban areas are often accepted.

21. URBAN ARTERIALS • Bikeways and Public Transit Facilities • Bikeways see AASHTO Guide for the Development of Bicycle Facilities • Public Transit • Facilities Design and operational features of public transit facilities( here just buses) on arterials are: • Locations of bus stops (spacing and location with respect to intersections) • Design of bus stops and turnouts • Reservation of bus lanes • Special traffic control measures.

22. URBAN ARTERIALS Bikeways and Public Transit Facilities Location of The general location of bus stops is largely dictated by Bus Stops patronage and by the locations of intersection but routesand traffic points. Bus stops at intersections may be located on the near ( approach) or far (department) side of the intersection. See Exhibit 7-17 Far side: reduce the conflict with other buses turning left or right, reduce the conflict with heavy traffic, reducing conflict with pedestrians. Near side: Sight distance Other vehicles are difficult in making turns.

23. URBAN ARTERIALS Bikeways and Public Transit Facilities Bus Turnouts Bus stops are clear of the lanes for through traffic. See Chapter 4. Reserved Bus exclusive use of bus lane is accomplished by offsetting the Lane division line on a multilane street. See Exhibit 7-18 Traffic Control Devices Traffic control devices on arterial streets are installed to favor for auto traffic.