Practical Highway Design Solutions (2013)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

46 Appendix C Missouri dOT practical design implementation Manual NOTE: The following are the Primary Guidance statements from the MoDOT Prac�cal Design Implementa�on Manual. TYPE OF FACILITY Facility Selection • For both major and minor routes, the type of facility will be based upon the desired level of service (LOS) given the 20-year traffic projec�on of the corridor. More specifically: o Peak Hour LOS ▪ Rural – D ▪ Urban – E o Off-Peak LOS ▪ Rural - C ▪ Urban - D • Irrespec�ve of LOS, Planning Division will con�nue to iden�fy the general types of facili�es for statewide system con�nuity. • The facility must represent the appropriate balance between access and mobility for its intended purpose. • When the desired LOS requires a four-lane facility, it will be designed as an expressway unless freeway is mandated. • Two-way le�-turn lanes (TWLTL) are permissible where prac�cal. • Passing lanes may be used in areas where poor LOS is a result of inability to pass safely. At-Grade Intersections • Signalized intersec�ons can be considered for expressways that pass through communi�es. • In rural areas, a designer is not to consider including a signalized intersec�on for expressways, although one may be installed at an exis�ng intersec�on with Traffic’s recommenda�on. • The minimum distance between intersec�ons along MoDOT roads is determined by whether the road is a major or minor road and whether the road is urban or rural. Refer to the Access Management Guidelines for desirable spacing between at-grade intersec�ons. Interchanges • An interchange is to be considered when it is warranted by the 20-year design traffic projec�on or safety concerns. • The desired spacing between interchanges is two miles in current and projected urban areas and five miles in rural areas. TYPICAL SECTION ELEMENTS Lane Width • Lanes on both rural and urban major roadways are to be 12 �. wide. • Lanes on rural and urban minor roadways are to be 10 to 12 �. wide, based on the volume of traffic and the context of surrounding roadway.

47 • Auxiliary lanes a� nterchanges facilitate traffic movements. These lanes are to be as wide as the through-traffic lanes. • Lane widths on very low volume local and collector roads and streets that carry less than 400 vehicles per day are to be based on the guidance contained in the AASHTO document Guidelines for the Geometric Design of Very Low Volume Local Roads Shoulder Width • Never eliminate shoulders altogether. Motorists expect them. • Shoulders on major roadways (both rural and urban) are to be 4 to 10 �. wide based on the volume of traffic, the percentage of trucks and context of the surrounding road. • Shoulders on rural minor roadways are to be 2 to 4 �. wide. • Shoulders will not be provided on urban roadways with no access control if ample turning opportuni�es exist for a vehicle to leave the roadway. • An earthen shoulder will be provided behind a mountable curb. • Rumble strips are to be provided on major and minor roadways with paved shoulders at least 2 �. wide (see Rumble Strip guidance for further informa�on). Median Width A wide separation between traffic moving in opposing direc�ons is safer and more comfortable for the motorist than head-to-head traffic in close proximity. While this works well in rural areas, it may be necessary in densely developed areas with expensive right of way to provide a narrower median with a posi�ve barrier. Therefore, the following items are important: • The preferred typical section for expressway and freeway facili�es will include a depressed median 60 �. wide, measured from edge of traveled way to edge of traveled way. A median of this width sa�sfies clear zone concepts. • A narrower median with a posi�ve barrier can be used on expressways and freeways if the decision is based upon an economic analysis. This situa�on is most likely to occur when the cost of right of way adjoining the improvement is expensive or when its ver�cal alignment causes high fills or deep cuts. Inslope Grade • The preliminary geotechnical report contains grading recommenda�ons including the slope ratio that is not to be exceeded. • The AASHTO Roadside Design Guide may be consulted to select the proper combina�on of inslope ratio and clear zone concept. • Use of guardrail is preferable to a 1V:6H/1V:3H (“barnroof”) design when addressing economic concerns (e.g. to balance earthwork quan�ties or to decrease the amount of R/W). Backslope Grade • The preliminary geotechnical report contains grading recommenda�ons including the slope ratio that is not to be exceeded. • When good quality rock is present, and grading recommenda�ons included benching, u�lize a 1:1 backslope from the back of the ditch to establish the theore�cal slope limit used to determine the R/W line.

48 Roadside Ditches • Roadside ditches are to be of sufficient depth to insure drainage from the design storm event and prevent seepage under the pavement through a permeable base. • When pavement edge drains are necessary, the roadside ditch must be of sufficient depth to permit loca�on of the drain above the water surface eleva�on during the pavement drainage design event. • Flat bo�om or V-ditches are to be selected for use based on hydraulic capacity and the inslope and backslope requirements necessitated by clear zone principles and/or soil condi�ons. • The ditch will be designed to meet the criteria set forth in the Roadway Overtopping Criteria section. • Necessary erosion control methods will be used in areas as determined by the district to reduce or withstand the flow velocity. HORIZONTAL AND VERTICAL ALIGNMENT Horizontal Alignment • Horizontal alignments are to be coordinated with anticipated posted speeds. • Chapter 3 of the AASHTO publica�on A Policy on Geometric Design of Highways and Streets (the Green Book) will be used as guidance to determine maximum horizontal alignments. • A rela�vely sharp curve may be designed if the curve is properly signed. Vertical Alignment • Ver�cal alignments are to be coordinated with anticipated posted speeds. • The AASHTO publication A Policy on Geometric Design of Highways and Streets (the Green Book) can be used as guidance to determine maximum vertical grades. • Every effort should be made during the design of a project to insure the quantities of fill and excavation are balanced (i.e., the excavation plus swell volume equals the fill plus shrinkage volume). PAVEMENTS Paved Shoulders • On major roads the en�re shoulder width should be paved. • On minor roads the shoulder should be aggregate stabilized except where maintenance or safety concerns (e.g., edge drop off, high runoff road occurrence) jus�fy a paved shoulder. • Shoulders on urban roadways with access control (major or minor) are to be paved. • In no case will a paved or aggregate surface be used directly behind a mountable curb along the outer edge of a roadway. • A curb and gu�er will only be used with an an�cipated posted speed less than 50 mph. Bridge Approach Slabs • Bridge approach slabs will be used on all major road bridges. The approach slabs will only be omi�ed by design excep�on not by a construc�on value engineering (VE) proposal. • On minor roads bridge approach slabs will not be used except with a design exception.

49 Pavement • The Construction and Materials Division will determine the pavement thickness for all projects on major roads. During early scoping, pavement thicknesses for conceptual design and es�ma�ng purposes may be obtained from the ME (Mechanis�c-Empirical) Design Table for Project Scoping. • On minor roads, for spot improvements such as pavement replacement less than 0.5 miles in length adjacent to bridge replacements, widening for turning lanes for a turning movement that has less than 1000 vehicles per day or for short realignments, a pavement thickness determina�on by Construc�on and Materials is not required. The new pavement thickness is to be equivalent to the exis�ng pavement thickness on 4 in. of aggregate base or 5 3/4 in. on 4 in. of aggregate base, whichever is greater. For these projects, the new pavement is to consist of asphalt (cold mix or hot mix) or concrete pavement, at the contractor’s op�on. If the AADT is between 1000 and 2000, the cold mix may be eliminated. If the AADT is greater than 2000, cold mix is not allowed. • On minor roads, for improvements greater than 0.5 miles in length or for widening for turning lanes for a turning movement with more than 1000 vehicles per day, the Construc�on and Materials Division will make a pavement thickness determination. During early scoping, pavement thickness for conceptual design and es�ma�ng purposes may be obtained from the ME (Mechanis�c-Empirical) Design Table for Project Scoping. • Superpave mixes are not appropriate for minor roads except for unusual circumstances with a design excep�on. • Aggregate surfaces will not be used except on very low volume or dead end road applica�ons, such as outer roads, temporary bypasses and roadways to be turned over to another agency. In these circumstances an aggregate surface may be appropriate if dust can be tolerated. For these situa�ons a minimum 2 in. thickness of gravel, crushed stone, or chat may be used. STRUCTURAL/HYDRAULICS Bridge Width • For Major roads, bridge width equaling full roadbed width is desirable. • For Minor roads, strive for 2’ shoulders (24 to 28 foot bridge width, depending on lane width). • Minimum width for all bridges is 24’. • Full shoulders are required for bridges over 1000’ long. Bridge and Culvert Hydraulic Design • Roadway Overtopping o Minor Routes ▪ For bridges and boxes, the water level shall be no deeper than 1 foot below the lowest shoulder point during a 25- to 50-year event. For pipes, the water level shall be no deeper than 1 foot below the lowest shoulder point during a 10- to 25-year event. o Major Routes ▪ For bridges and boxes, the water level shall be no deeper than 1 foot below the lowest shoulder point during a 50- to 100-year event. For interstates use the 100-year event. For pipes, the water level shall be no deeper than 1 foot below the lowest shoulder point during a 25- to 50-year event. For interstates use the 50-year event.

50 • Freeboard for Bridges on All Routes o For a drainage area less than 20 square miles, the bridge shall have 1 foot of freeboard during a 50-year event. For a drainage area greater than 20 square miles, the bridge shall have 2 feet of freeboard during a 50-year event. • Backwater/Headwater for bridges, box culverts and pipes on all routes shall meet the National Flood Insurance Program requirements. The designer must consider the impacts to upstream improvements, crops and property values as well as the depth, frequency, extent and dura�on of the backwater impacts. The backwater must be reasonable for the full range of flows less than or equal to the design event. “Impact,” is defined in terms of value and quantity of property that may be affected. Prior to selec�ng backwater criteria, the poten�al backwater impacts are evaluated: o For bridges and boxes in areas with low levels of potential impact, allow from 0 to 2 feet of backwater over natural in a 100-year event. In areas with moderate to high poten�al impact allow 0 to 1 foot of backwater over natural in a 100-year event. o For pipes with upstream impacts that may be moderate to high, analyze backwater and consider impacts from depth, extent and frequency of flooding for the range of flows. • The Design High Water Eleva�on (DHW) will be based on the return period of the freeboard design. • Design excep�ons for frequency or criteria are encouraged when they are practical. • When an exis�ng structure that is to be replaced has provided adequate performance, a design excep�on to match the hydraulic performance of the exis�ng structure is necessary and encouraged. Thorough documenta�on of the adequate historical performance is included with the Design Exception. Seismic Design • Seismic design of bridges is guided by the AASHTO design specifica�ons, which delineate seismic zones in Missouri. • New bridges on major roads and Earthquake Emergency Routes are modeled (comprehensively analyzed) and designed to resist earthquakes according to Seismic Performance Categories (SPC) B, C and D. • New bridges on minor routes in SPC B, C and D, include limited seismic details to improve their resistance to earthquakes; however, they are not modeled (comprehensively analyzed) and specifically designed to resist earthquakes. • A decision is made on each bridge rehabilita�on project as to the necessity and extentof seismic retrofi�ng. ROADSIDE SAFETY Rumble Strips • All major roads will have edgeline rumble strips. • All major 2-lane roads with new pavement will have centerline rumble strips. • Edgeline rumble strips may be used on minor roadways as a specific safety countermeasure with a paved shoulder. Where several sec�ons of edgeline rumble strips are installed in close proximity, con�nuity should be maintained. • Centerline rumble strips may be used on minor roadways with a significant accident history. Where several sections of centerline rumble strips are installed in close proximity, con�nuity should be maintained. • Rumble strips are omi�ed where the posted speed limit is less than 50 mph.

51 Guardrail • The clear zone concept is the preferred method of providing roadside safety. • If providing the proper clear zone is imprac�cal, then shielding (concrete barrier, guardrail, or guard cable) is preferred. If shielding is also imprac�cal, the obstacle must be delineated as a final, but least preferred, alterna�ve. • Shielding should be specified when the possibility of poor public perception of the clear zone exists, especially in areas of high fill. INCIDENTAL/MISC. Disposition of Routes • A wri�en agreement for disposi�on should be in place before a project is placed on the STIP. • During project development, if a wri�en agreement is revoked, then the project will be removed from the STIP. A written agreement must be in place before a project is advertised for le�ng. • It is acceptable to nego�ate small improvements to the exis�ng route in order to make the relinquishment more a�rac�ve. Bicycle Facilities MoDOT values the needs of all customers including non-motorized travelers. The provision of bicycle facili�es on improvement projects during planning, and design activi�es is necessary when any one or more of the following condi�ons exist: • The local jurisdiction has a comprehensive bicycle policy in the area of the proposed improvement. • There is public support through local planning organiza�ons for the provision of bicycle facili�es. • The local jurisdiction agrees to fund the total cost of the facility (right of way and construc�on) plus the provision of future maintenance. • Bicycle traffic generators are located near the proposed project (i.e., residen�al neighborhoods, employment centers, shopping centers, schools, parks, libraries, etc.). • There is evidence of bicycle traffic along the proposed project or the local community supports the incorporation of facili�es at this �me. • The route provides access across a natural or man-made barrier (i.e., bridges over rivers, roadways, or railroads or under access controlled facili�es). Dedicated bicycle facili�es will not be provided on interstate roadways. Pedestrian Facilities MoDOT values the needs of all of its customers including non-motorized travelers. The provision of pedestrian facili�es on improvement projects during planning, and design ac�vities is necessary when any of the following condi�ons exist: • The local jurisdiction has a comprehensive pedestrian policy in the area of the proposed improvement. • There is public support through local planning organiza�ons for the provision of pedestrian facili�es.

52 • Pedestrian traffic generators are located near the proposed project (i.e., residen�al neighborhoods, employment centers, shopping centers, schools, parks, libraries, etc.). • There is evidence of pedestrian traffic along the proposed project or the local community supports the incorporation of facili�es at this �me. • The route provides access across a natural or man-made barrier (i.e., bridges over rivers, roadways, or railroads or under access controlled facili�es). • Exis�ng sidewalks are disturbed by construc�on. When sidewalks are constructed the following items are to be considered: • In developed areas, sidewalks are to be separated from the traveled way by a barrier curb. • Sidewalks are not to be designated on paved shoulders located behind a mountable curb. • In rural areas where it is necessary to accommodate pedestrian movements, a paved shoulder may be used. • Designated sidewalks or pedestrian paths must be accessible according to the Americans with Disabili�es Act of 1990 (ADA). • Sidewalks are to be a minimum of 5 �. wide and 4 in. thick. However, if necessary, the width of the sidewalk can be reduced to 4 �., the minimum width allowed by ADA guidelines. • Addi�onal guidance regarding sidewalk design can be found in the AASHTO publica�on Guide for the Planning, Design, and Opera�on of Pedestrian Facili�es or the Americans with Disabili�es Act Accessibility Guidelines (ADAAG) publica�on Part 2 Designing Sidewalks and Trails for Access. • Technical assistance on a case-by-case basis is also available from the Missouri office of the United States Access Board or MoDOT’s Bicycle and Pedestrian Program Coordinator. Embankment Protection • Rock blanket is used under the ends of all grade separa�on structures, around bridge end slopes, around culverts and to protect stream banks. • Concrete slope protection may be used for aesthe�c reasons to prevent slope erosion under the ends of grade separa�on structures or other locations. Borrow and Excess Earthwork • When borrow material is necessary on a project, the contractor will be required to locate a sa�sfactory site from which the necessary material can be obtained. • On rare occasions (i.e., highly sensi�ve environmental or cultural areas) a commission furnished borrow site may be provided. When this is done, the site is indicated on the plans and the contractor must use the site to obtain the borrow material. • When it is necessary to dispose of excess material, the above guidance is to be used. Minimum Right of Way Width • Acquire only the minimum R/W width needed to build and maintain the facility. • A�empt to minimize breaks in R/W line.

53 Design Exception • Design excep�ons are encouraged wherever the poten�al for addi�onal value lies outside of wri�en engineering policy. • Design excep�ons, using the standard form, must be completed and approved for each variance, whether the change fails to a�ain or exceeds engineering policy. • A slightly different produc�on and approval process exists for each of the following project categories: 1. Full FHWA Oversight Projects 2. Exempt Roadway Projects 3. Exempt Bridge Projects 4. Consultant Designed or Cost Share Projects