Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance (2022)

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101   A P P E N D I X B Agency Survey Responses

102 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Responding Agency State Code Alabama DOT AL Arizona DOT AZ Arkansas DOT AR California DOT CA Colorado DOT CO Connecticut DOT CT Delaware DOT DE Florida DOT FL Idaho Transportation Department ID Illinois DOT IL Indiana DOT IN Iowa DOT IA Kansas DOT KS Louisiana DOTD LA Maine DOT ME Maryland DOT MD Massachusetts DOT MA Michigan DOT MI Minnesota DOT MN Mississippi DOT MS Missouri DOT MO Montana DOT MT Nebraska DOT NE Nevada DOT NV New Jersey DOT NJ New Mexico DOT NM New York DOT NY North Carolina DOT NC North Dakota DOT ND Oklahoma DOT OK Oregon DOT OR Pennsylvania DOT PA South Carolina DOT SC South Dakota DOT SD Tennessee DOT TN Texas DOT TX Utah DOT UT Virginia DOT VA Washington State DOT WA Wisconsin DOT WI Wyoming DOT WY

Agency Survey Responses 103   Q1 – Does your agency currently use subsurface drainage systems? If not currently used, please indicate why. State Currently used Never used Usage discontinued due to Other Poor performance Construction issues Maintenance issues Cost issues Totals 31 1 7 1 5 0 1 AL ü AZ ü AR ü CA ü CO ü CT ü DE ü FL ü ID ü IL ü IN ü IA ü KS ü ü ü LA ü ME ü MD ü MA ü MI ü MN ü MS ü ü MO ü MT ü NE ü NV ü NJ ü NM ü NY ü NC ü ND ü ü OK ü OR ü PA ü SC ü ü SD ü TN ü TX ü UT ü VA ü WA ü WI ü WY ü Other: State Response AZ We don't have a policy or standard practices relative to subsurface drainage. Additional Comments/Clarifications: State Response ND Subsurface drainage (permeable stabilized based course with edge drains) was used for a while under plain jointed concrete pavements on the interstate. The additional costs didn't seem to be translating to increased performance. Maintenance of the edge drains was also an issue. WA WSDOT uses crushed stone base course as a drainage layer on most projects. WY Wyoming used edge drains for many years but discontinued because of clogging issues. Additionally, we had a pilot project a few years ago where we used a wicking geotextile under the pavement. The product was expensive, so it was only used in a small test section known to have drainage issues.

104 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q2 – Please indicate all locations/conditions where subsurface drainage systems are installed. State During all new concrete pavement construction During all new asphalt pavement construction Only when usage meets established criteria In all sag locations In all cut/fill transitions Only on full-depth widening adjacent to roadway with existing subsurface drainage Decision to incorporate is pending Other Totals 8 8 19 8 2 4 1 12 AL ü AR ü ü CA ü ü ü ü ü ü CO ü CT ü DE ü FL ü ü ID ü IL ü IN ü ü IA ü ü ü KS ü LA ü ME ü ü MD ü ü MA ü MI ü ü MN ü MS MO ü MT ü NE ü ü NV ü NJ ü NY ü ü ü NC ü ü ü ND ü OK ü OR ü PA ü ü ü ü SC ü SD ü TN ü TX ü UT ü VA ü ü ü WA ü ü WI ü ü

Agency Survey Responses 105   Q2 (Cont.) – Please indicate all locations/conditions where subsurface drainage systems are installed. Other: State Response AL During new pavement construction/re-construction if site conditions warrant. CA Depending on site conditions and project climate zone. CO Subsurface drainage systems are installed at locations based primarily on maintenance feedback or site-specific geotechnical findings/recommendations. Can vary seasonally depending on the amount of moisture received. Have used in mountain locations where pavement distress is evident due to freeze/thaw action. FL Underdrains are sometimes used on asphalt roadways in areas of high groundwater; however, this is not the most desirable option as it can create maintenance issues. ID Subsurface drainage components are used on a case-by-case basis to address specific concerns at project level. ME Underdrain boxed section is used where curb and gutter design is incorporated, typically in more urban settings where ditches are difficult due to property impacts. Also in areas where the open-graded sand and gravel sub-base cannot be daylighted in the ditch section. MN Each district decides when to use a subsurface drainage system under concrete pavement. There is no subsurface drainage system under asphalt pavement. MT We only install a drainage system when determined to be needed, based on many factors, including surfacing, geotechnical, maintenance, construction, and personnel factors. It is pretty rare in Montana to install a drainage system. NC We use drainage components where subgrade is not free draining. In these areas continuous drains are used for concrete pavement. For asphalt pavements we use drains where ADT is greater than 40,000 and trucks are greater than 15%. Drains are considered where ADT is greater than 15,000 and trucks are greater than 5%. ND Currently subsurface drainage systems are only used in locations of known high-groundwater issue. They are more commonly used by cities in urban (curb & gutter) sections. NJ Subsurface drainage systems are installed in new pavements that are determined to require them based on subsurface investigation of the roadway foundation. They may also be installed on existing pavements during rehabilitation of pavements that have been identified as having subsurface drainage issues. SC Drains are only used when there is a drainage issue with an existing pavement that has been identified by maintenance forces as causing poor long-term pavement performance. It is a case-by-case decision based on a subjective assessment of need versus established objective criteria. This is a rare occurrence. Additional Comments/Clarifications: State Response AR Pipe underdrains are used for all Interstate construction. Pipe underdrains are used on other highways in locations where they are determined to be needed. This includes sags and other locations at which the field engineer determines they are needed. IL Used mostly on the Interstate system and other freeway facilities that are designed to Interstate criteria. IN INDOT uses subsurface drainage systems for high-volume traffic roadways and as per soil report. We definitely use subsurface drains when we use an open-graded drainage layer in the pavement system. KS Historically, KDOT installed subsurface drainage systems under all full-depth concrete and asphalt pavements beginning in the late 1980s. The subsurface drainage systems comprised a drainable base layer that was essentially a porous asphalt material or a porous cement-treated base. Additionally, longitudinal edge drains were also installed during this period of time. After constructing drainable base layers for roughly 15 years, it was decided to cease this practice due to poor performance of the pavement structure. After constructing longitudinal edge drains for approximately 20 years, it was decided to end this practice as well, due mostly to construction-related issues, including incorrect installation, bent pipes, contractors running over pipe outlets, and lack of maintenance by field staff. LA The department has a Road Design Manual and Engineering Directives and Standards. Subsurface systems are installed where drainage is needed to properly drain the pavement section. Typically, drainage is required when concrete paving is adjacent to an asphalt shoulder or an aggregate base is adjacent to an embankment. Non-plastic embankment is typically used for the aggregate base scenario. MD Continuous subsurface drainage or subsurface just at low/sag locations, based on roadway functional class. MI It is not used in all new pavement construction. Drainage systems are not always used where sandy subgrades create good vertical drainage. NM We (NMDOT) only have one project where we have used permeable concrete; as we are in the arid SW, we don't have extensive underdrain systems. SC We have not had a lot of success when pavement drainage systems have been used in the past because of poor performance related to material properties (stripping in asphalt drainage layers) and maintenance issues (drains are forgotten over time and not kept up), which result in poor pavement performance. TX When internal drainage is contemplated for use within the pavement structure, the department’s focus since 1994 on conducting a full drainage analysis has been to restrict it to: (1) rigid structures and full-depth HMA > 8 in. thick, (2) where rainfall is 20 in./yr or more, and (3) where ADT > 7500 vpd. Exceptions: when the proposed design has given good performance in the past, adequate ditches cannot be constructed due to ROW restrictions, future maintenance of longitudinal edge drains cannot be accomplished, or it is located in urban areas where frequent work may be needed, when movement is expected in full-depth HMA due to swelling clay soils, or where fast-track construction is required or subbase must carry traffic during construction. WA WSDOT considers subsurface drainage on all projects.

106 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q3 – Please indicate how the need for subsurface drainage systems is assessed. State Overall surface drainage Climactic influences Highway geometrics Groundwater levels Soil types Proposed base materials Historical roadway distress Structural Capacity of Existing Pavement Potential impacts on adjacent wetlands Other Totals 24 11 29 30 26 18 31 6 7 4 AL ü ü AR ü ü ü ü ü CA ü ü ü ü ü ü ü CO ü ü ü ü CT ü ü ü ü ü ü ü ü DE ü ü FL ü ü ü ü ü ü ID ü ü ü ü ü ü ü IL ü ü ü IN ü ü ü ü ü ü ü IA ü ü ü KS ü ü ü ü ü ü LA ü ü ü ü ME ü ü ü ü ü ü ü ü ü MD ü ü ü ü ü ü MA ü ü ü ü MI ü ü ü ü MN ü ü ü MS MO ü ü ü MT ü ü ü ü ü ü ü ü NE ü ü ü ü NV ü ü ü ü ü ü ü NJ ü ü ü ü NY ü ü ü ü ü ü ü ü NC ü ü ü ND ü ü ü OK ü ü ü ü ü ü ü ü OR ü ü ü ü ü PA ü ü ü ü ü ü SC ü ü SD ü ü ü ü ü ü TN ü ü ü TX ü ü ü ü UT ü ü ü ü ü VA ü ü ü ü WA ü ü ü ü ü ü ü ü ü WI ü ü ü ü Other: State Response KS Historically, unbound drainable base was considered under flexible pavements when the design lane daily ESALs exceeded 265. MN Based on past experience with a particular roadway segment. SC Continuous maintenance issues where trapped water in the pavement structure is known to have contributed to a structural pavement failure. TX Rigid pavements with flexible pavement shoulders with a shallow water table during construction, or natural springs. Additional Comments/Clarifications: State Response IN INDOT uses new subsurface drains for selected roadway reconstruction/new pavement and uses retrofit underdrains with a few rehabilitation techniques such as crack and seat, and rubblization of concrete pavement. TN Underdrains have been added in areas where there were documented pumping issues and poorly draining soil. Due to cost, use of drains was focused on sag areas or the lower side of superelevated areas. TX It is our policy that new rigid pavements are built using two non-erodible base options: 4 in. HMA or 6 in. cement-treated base + >1 in. bond breaker.

Agency Survey Responses 107   Q4 – Please indicate the method(s) used for subsurface drainage system design. State DRIP or DRIP 2.0 software In-house software Standardized designs Other Totals 2 3 31 5 AL ü AR ü CA ü CO ü CT ü DE ü FL ü ID ü ü IL ü IN ü IA ü KS ü LA ü ME ü ü MD ü MA ü MI ü MN ü MS MO ü MT ü NE ü ü NV ü ü NJ ü NY ü NC ü ND ü OK ü OR ü PA ü ü SC ü SD ü TN ü TX UT ü VA ü WA ü WI ü Other: State Response CO Based on our 2019 M&S Standards detail M-605-1 Subsurface Drains and using guidance in the CDOT Drainage Design Manual. ID Our materials manual recognizes and encourages the use of DRIP. However, most designs are left to the engineer of record to establish. MT Systems are designed on a case-by-case basis and are usually just designed with some conservative assumptions. ND They are designed to address specific high-groundwater issues. OR Standard details with project-specific designs based on performance of adjacent systems or other methods. Additional Comments/Clarifications: State Response IN INDOT uses subsurface drainage systems based on site-specific conditions like high-volume traffic, soil type, and open-graded drainage layer. MI Standard Plan series R-80 contains our standard designs. R-80 can be found here: https://mdotjboss.state.mi.us/stdplan/standardPlansIndex.htm#roadPlans. PA Nomographs are used for maximum outlet spacing design. The Stormwater and Drainage menu from OpenRoads Designer© is used. TX The department's focus on pavement drainage design has been on minimizing surface moisture infiltration through techniques such as constructing adequate cross slope, maintaining proper ditch depth, using non-moisture-susceptible materials, and aggressive use of sealcoats and crack sealing, rather than on establishing internal features.

108 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q5 – Please indicate the source(s) of water that subsurface drainage systems are used to intercept. State Rainwater entering vertically through joints and cracks Snow meltwater entering vertically through joints and cracks Vapor movements Groundwater entering horizontally Groundwater entering vertically through capillary action Groundwater rising vertically due to seasonal or long-term fluctuations Other Totals 31 20 8 29 27 28 0 AL ü ü ü ü AR ü ü ü ü CA ü ü ü ü ü ü CO ü ü ü ü ü ü CT ü ü ü ü DE ü FL ü ü ü ü ID ü ü ü ü ü IL ü ü IN ü ü ü ü ü ü IA ü ü ü ü ü KS ü ü ü LA ü ü ü ü ü ME ü ü ü ü ü MD ü ü ü ü ü MA ü ü ü MI ü ü ü ü ü MN ü ü ü ü ü MS MO ü ü ü MT ü ü ü ü NE ü ü ü ü ü NV ü ü ü ü NJ ü ü ü ü ü ü NY ü ü NC ü ü ND ü ü ü OK ü ü ü OR ü ü ü PA ü ü ü ü ü SC ü ü SD ü ü ü ü ü ü TN ü ü TX ü ü UT ü ü VA ü ü ü WA ü ü ü ü ü WI ü ü ü Additional Comments/Clarifications: State Response PA Frost-heave is a concern for our Department. SC Drainage layers are used in rare occurrences and are not a continuous layer when utilized.

Agency Survey Responses 109   Q6 – Please indicate the decision factor(s) used to incorporate subsurface drainage systems. State When in- house decision criteria are met Results of life- cycle cost analysis Pavement type Proposed base materials Historical pavement distress Continuous maintenance issues related to excess moisture Projected traffic Subgrade properties Precipitation rates Other Totals 25 3 13 19 26 34 4 24 5 4 AL ü ü ü ü AR ü ü ü ü ü CA ü ü ü ü CO ü ü ü ü ü CT ü ü ü ü DE ü FL ü ü ü ü ü ID ü ü ü ü ü IL ü ü ü ü IN ü ü ü ü ü IA ü ü ü ü KS ü ü ü ü ü LA ü ü ü ME ü ü ü ü ü ü ü ü MD ü ü ü ü ü ü MA ü ü ü ü ü MI ü ü ü MN ü ü MS MO ü ü ü MT ü ü ü ü ü ü NE ü ü ü ü ü NV ü ü ü ü ü ü NJ ü ü ü ü ü NY ü ü ü ü ü NC ü ü ü ü ND ü ü OK ü ü ü ü ü ü ü OR ü ü ü PA ü ü ü ü ü SC ü SD ü ü ü ü ü ü ü TN ü ü TX ü ü UT ü ü ü ü VA ü ü ü ü ü ü WA ü ü ü ü WI ü ü Other: State Response CO Site-specific geotechnical/groundwater information or where seepage is encountered/present. MI In preparation for rubblization of an existing concrete pavement if there is not an existing drainage system. Also in preparation for an asphalt-stabilized crack relief layer (ASCRL) project. PA The preferred method is to daylight the subbase to a roadside swale. If the physical site parameters prohibit this, then subsurface drainage is installed. TX During construction when water is contributing to pavement failures. Additional Comments/Clarifications: State Response ID We don't have formal criteria but require a fairly detailed roadway materials report that addresses potential sources of water, historical maintenance issues, subgrade soils, topography (cut/fill transitions), etc.

110 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q7 – Please indicate how permeable base layer thickness is determined. State Permeable base layers are not used by our agency Determined based on infiltration computations Standardized at 100 mm Standardized at 150 mm Determined based on agency design standards for structural layer components Other Totals 12 2 9 5 14 5 AL ü AR ü CA ü CO ü CT ü DE ü FL ü ID ü IL ü IN ü ü IA ü ü KS ü ü ü LA ü ME MD ü MA ü MI ü ü MN ü MS MO ü ü ü MT ü NE ü ü ü NV ü NJ ü NY ü NC ü ND ü OK ü OR ü ü PA ü SC ü SD ü TN ü TX ü UT ü VA ü ü WA ü WI ü

Agency Survey Responses 111   Q7 (Cont.) – Please indicate how permeable base layer thickness is determined. Other: State Response IA For a pavement that has subdrains on both sides of the roadway, a uniform 6-in. thickness is used. On four-lane facilities, there is one subdrain at the outside pavement edge. In this case, the subbase is asymmetrical and is sloped at 1% to the outside, and the subbase is 6 in. thick at the inside pavement edge, 10.3 in. at the centerline, and 8.9 in. at the outside pavement edge. IN INDOT uses a 3-in. HMA OG layer as a drainage layer. MI We have one region where the standard permeable base thickness is 406 mm (16 in.). MO 18 in. daylighted rock base. VA Permeable base thickness can range up to 12 in. Additional Comments/Clarifications: State Response CO Generally, permeable base materials are not used. However, we have rubblized existing concrete pavement in place, which has resulted in a fairly permeable base layer, and we have stabilized soft subgrade materials using our "filter material," which consists of a clean angular crushed rock/gravel, again very permeable. Drainage systems have been installed in some of these applications. Where seepage is present during construction, we have installed an underdrain to intercept the water and drain it from beneath the roadway or embankment as needed, but no official design was done; a standardized thickness was stipulated in the plans. ID Most of our state has low rainfall and we haven't had the need for formal flow calculations. IL Experimental sections were constructed using cement-stabilized and asphalt-stabilized open-graded drainage layers in the past, but their use has been discontinued. ME Permeable base layers are not used routinely. We have constructed several on trial projects. We use permeable base layers occasionally on full-depth porous pavement sections. MO For new construction or reconstruction of interstate pavement, the standard drainable layer is a 4-in. permeable cement- or asphalt- treated base. For other principal arterial routes, a 4- to 6-in. unbound crushed stone base is specified. For any of these pavement types, an 18-in. daylighted rock base is always acceptable if the profile grade allows. MT Typically, a specific drainage layer is not included; we just use a well-graded base course, which can have a permeability that is much higher than the subgrade soil but is less than what would be considered "free draining.” We have installed some free-draining materials where a known/problematic frost heave occurs, but this is pretty rare. NC We now use non-woven geotextile interlayers in lieu of permeable base layers. ND In the past, a cement-stabilized base layer 4 in. thick was used under concrete paving. NY Type 2 asphalt-treated permeable base (ATPB) is the only treated permeable base allowed and is used only with HMA pavements. OR Permeable base thickness requirements based on infiltration computations are not included in design criteria but would be used in a manner consistent with pavement and geotechnical standard of practice. This is also based on experience, depending on the level of soil variability along the project. TX Only test sections have been placed; edge drains are not commonly used. VA For porous pavement applications that have been used in parking lot applications, the thickness requirement is based on infiltration computations. For roadway pavements, the thickness is based on local experience and material type. WA WSDOT standard bases are permeable. WSDOT does not typically use open-graded permeable bases.

112 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q8 – Please indicate how permeable base layers are constructed. State Permeable base layers are not used by our agency Using unstabilized aggregates Using cement- stabilized aggregates Using asphalt- stabilized aggregates Previously using unstabilized aggregates, cement stabilization currently allowed or required Previously using unstabilized aggregates, asphalt stabilization currently allowed or required Previously using highly permeable aggregates, denser gradation currently specified Only within roadway shoulders Other Totals 13 20 8 15 1 4 4 0 3 AL ü ü AR ü CA ü ü ü ü ü CO ü CT ü DE ü ü ü ü FL ü ID ü ü IL ü IN ü ü ü IA ü ü KS ü LA ü ü ü ME ü ü MD ü MA ü MI ü ü MN ü ü MS MO ü ü ü MT ü NE ü ü NV ü ü ü NJ ü ü NY ü NC ü ü ND ü OK ü OR ü ü PA ü ü ü SC ü SD ü TN ü ü TX ü UT ü VA ü ü ü WA ü WI ü ü

Agency Survey Responses 113   Q8 (Cont.) – Please indicate how permeable base layers are constructed. Other: State Response MI Very rarely, the permeable base layer will be stabilized with cement. NC We now use nonwoven geotextile interlayers in lieu of permeable base layers. NE We primarily use crushed concrete as permeable base material, but we allow unstabilized aggregates or bit millings. Additional Comments/Clarifications: State Response AL To date, only permeable asphalt-treated base layers have been constructed. CA Cement-stabilized (cement-treated permeable base) and asphalt-stabilized (asphalt-treated permeable base) aggregates have been used in California pavements for a long time. CO See comments in prior question. Infrequent/non-standard use of permeable base layers. DE We have previously used cement- and asphalt-treated bases. However, we have encountered failures in these designs recently and have discontinued their use. IA Our drainability has been reduced due to some changes in gradation for our bases that need to be more stable to carry construction traffic, improve constructability, and pad line for the paver. ID We have used asphalt-treated permeable leveling courses under our PCC pavements. This was typically done prior to 2010. IL Experimental sections were constructed using cement-stabilized and asphalt-stabilized open-graded drainage layers in the past, but their use has been discontinued. KS We used to construct both cement-stabilized aggregate and asphalt-stabilized aggregate bases. This practice has been discontinued as of the mid-2000s. We now only allow unstabilized aggregate bases as drainage layers. MA Permeable base layers were constructed on a past demonstration project but are not currently utilized except under porous pavements. ND In the past, cement-stabilized permeable base layers were used. NY Type 1 cement-treated permeable base (CTPB) has been eliminated altogether. Type 1 permeable base was not that widely used because it could not be paved over for 24 hours once it was placed. Additionally, CTPB and ATPB have been eliminated for PCC. OR Permeable asphalt-treated base sections were also previously used under CRCP but are no longer used because bonding between the CRCP and base adversely affected pavement performance. SC Permeable base layers were previously constructed using asphalt stabilization and unstabilized aggregates. TX A permeable base is used as part of the underdrain system in spot locations. VA Unstabilized and asphalt-treated aggregate bases are predominantly used. Cement-stabilized aggregate bases have been used previously and are still an option.

114 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q9 – Please indicate how the permeability of permeable base layers is established. State Permeable base layers are not used Using moderately permeable gradations Using highly permeable gradations Previously with highly permeable aggregate gradation, now with denser gradation with moderate to low permeability With no specifications for in-place hydraulic conductivity With in- place hydraulic conductivity specified at >100 ft/day With in-place hydraulic conductivity specified at >500 ft/day With in-place hydraulic conductivity specified at >1,000 ft/day With in-place hydraulic conductivity determined based on time to 50% drainage With in-place hydraulic conductivity determined based on time to 85% drainage Other Totals 12 8 7 5 17 0 0 2 1 0 3 AL ü AR ü CA ü CO ü CT ü DE FL ü ID ü IL ü IN ü ü ü IA ü ü ü KS ü ü LA ü ME ü ü MD ü ü MA ü MI ü MN ü ü ü ü MS MO ü ü MT ü NE ü ü NV ü ü NJ ü NY ü NC ü ND ü OK ü OR ü ü PA ü ü ü SC ü SD ü TN ü TX ü UT ü VA ü ü WA ü WI ü ü ü Other: State Response ME Permeable base layers are part of a porous pavement design. Typical selection includes uniformly-graded 2 in. reservoir stone layer and asphalt-treated permeable base layer. PA Must be "free draining.” WI Conductivity is not specified but is assumed to be about 1000 ft/day. Additional Comments/Clarifications: State Response AL The gradation is essentially AASHTO #57. CA Standard aggregate gradation is specified for cement/asphalt stabilized bases. IL Research currently underway to examine the use of moderately drainable aggregate layers under lower-volume concrete pavements. MA Permeable base layers were constructed on a prior demonstration project but are not currently utilized except under porous pavements. ME Site conditions and environmental requirements determine the in-place hydraulic conductivity and time to drain. MN Currently transitioning from highly permeable to moderate permeable aggregate gradation. MO Our permeable treated bases should have flows > 1000 ft/day, while our unbound bases would be well under 1000 ft/day.

Agency Survey Responses 115   Q10 – Please indicate how water collected by the permeable base layers is transmitted away from the pavement. State Permeable base layers are not used Underlying geotextile or wicking geotextile daylighted to side slope Longitudinal edge drains Transverse outlets Other With porous aggregate backfill and slotted pipes With porous aggregate backfill and preformed geocomposite edge drain Preformed geocomposite with no porous aggregate backfill With concrete headwalls spaced at intervals up to 250 ft With concrete headwalls spaced at intervals >250 ft With unprotected pipe ends spaced at intervals up to 250 ft With unprotected pipe ends spaced at intervals >250 ft Totals 9 12 28 7 3 9 10 3 1 4 AL ü ü AR ü ü CA ü ü ü CO ü ü ü CT ü DE ü ü FL ü ID ü ü IL ü ü ü IN ü ü IA ü ü KS ü LA ü ü ü ME ü ü ü MD ü ü ü MA ü ü MI ü ü ü MN ü ü MS MO ü ü MT ü ü ü ü NE ü ü ü NV ü ü ü ü ü NJ ü ü ü NY ü ü ü ü NC ü ü ND ü OK ü ü OR ü ü ü PA ü ü ü SC ü SD ü ü TN ü TX ü ü UT ü ü ü VA ü ü ü WA ü WI ü

116 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q10 (Cont.) – Please indicate how water collected by the permeable base layers is transmitted away from the pavement. Other: State Response ID Specific transmission system designs are left to the pavement materials engineer when required. ME We use a number of designs that are site-specific and dependent on known water issues and soil/roadway strength calculations. MI MDOT is currently piloting a new ending that is a poured-in-place concrete pad. The pad is 5 ft wide and the length is dependent on the grade of the fore slope. NE Primarily use granular edge drains and daylight every 250 ft. Additional Comments/Clarifications: State Response KS Longitudinal edge drains used to be constructed with porous aggregate backfill and slotted pipe conduits, but this practice was discontinued for several reasons back in the mid-2000s. MI Outlets are spaced at 300 ft maximum. Endings can be steel, concrete, or concrete ring. We have begun experimenting with other ending types. MT We have installed edge drains using various configurations, but they normally don't include a permeable base layer. NC We tie shoulder drains to drainage boxes wherever possible. NJ Underdrainage pipes are typically outlet into existing drainage inlet structures. When no inlet structures exist, then underdrain pipes are daylighted on rip-rap protected slopes. OR Note, answers are for permeable sub-base in certain locations only. Asphalt or concrete is always placed on a dense-graded base. PA Transverse outlets with concrete headwalls in areas of mowing, and unprotected when not exposed to equipment, spaced as per design nomograph. SD Typical for us is to use transverse outlets with concrete headwalls spaced at intervals of 500 ft or as needed for drainage. So, typically greater than 250 ft but it may be reduced in certain circumstances.

Agency Survey Responses 117   Q11 – Please indicate the method(s) used to increase stability of the permeable layer during construction. State Permeable base layers are not used No modifications required A denser gradation is now used A higher fractured face count is now used A minimum resilient modulus is now required Asphalt stabilization of the permeable layer is now required Cement stabilization of the permeable layer is now required Asphalt stabilization of the permeable layer is now allowed at contractor’s discretion Cement stabilization of the permeable layer is now allowed at contractor’s discretion Other Totals 13 20 6 1 0 3 1 2 0 0 AL ü ü AR ü ü ü CA ü CO ü CT ü DE ü FL ü ID ü ü IL ü IN ü ü IA ü ü KS ü LA ü ME ü MD ü MA ü ü MI MN ü MS MO ü MT ü NE ü NV ü NJ ü ü NY ü NC ü ND ü OK ü OR ü PA ü ü ü SC ü SD ü TN ü TX ü UT ü VA ü WA ü WI ü Additional Comments/Clarifications: State Response AL We allow the use of polymer-modified AC if there is a problem with paving on top of the permeable base layer. ID Our standard materials specifications call for a fractured face count for our permeable materials in order to avoid "ball bearings" under construction traffic. IN We have recently started using asphalt-stabilized permeable base under concrete pavement. ME Asphalt-treated permeable base is used on porous pavement sections to stabilize the roadway before OGFC application. MI Cement stabilization has been used on occasion. It serves two purposes: added stability for high-volume routes and stopping leachates when using recycled concrete in the base layer. The gradation for our open-graded drainage course was densified slightly 10-15 years back. MO Our permeable treated base designs have not changed in over 20 years, partly because Missouri has done very little interstate reconstruction and therefore has not been forced to re-examine specification deficiencies. NY Type 1 cement-treated permeable base (CTPB) was not that widely used because it could not be paved over for 24 hours once it was placed. Type 1 cement-treated permeable base (CTPB) has been eliminated altogether. Additionally, CTPB and ATPB have been eliminated for PCC. Type 2 asphalt-treated permeable base (ATPB) is the only treated permeable base allowed and is used only with HMA pavements. WI Practice has been discontinued.

118 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q12 – Please indicate the method(s) used to protect the permeable layer from contamination during construction. State Permeable base layers are not used No specific requirements enforced Construction and/or local traffic restricted prior to final surfacing Construction and/or local traffic prohibited prior to final surfacing Other Totals 14 5 13 5 1 AL ü AR ü CA ü CO ü CT ü DE ü FL ü ID ü IL ü IN ü IA ü KS ü LA ü ME ü MD ü MA ü MI ü MN ü MS MO ü MT ü NE ü NV ü ü NJ ü NY ü NC ü ND ü OK ü OR ü PA ü SC ü SD ü TN ü TX ü UT ü VA ü WA ü WI ü Other: State Response MI Contractors are allowed to drive on the permeable base layer if they provide an additional 2 in. for that layer and then remove those 2 in. prior to paving. The gradation is checked before and after placement. Additional Comments/Clarifications: State Response CO When permeable materials have been placed to intercept seepage or groundwater, they have generally been wrapped with a filter fabric and not opened to traffic beforehand, or not until a layer of protective earth/base has been placed on top of the filter fabric. ME In general, traffic on an unprotected permeable layer is prohibited except in areas where traffic coming out of side roads/residences/ businesses may need to cross over it. NC Traffic is restricted on top of the nonwoven geotextile interlayers we use in lieu of permeable bases. SD Construction and/or local traffic is typically restricted, and the permeable base layer is typically protected (prime and blotter or mag chlorides) prior to final surfacing. TN Would be impossible to finish construction without some construction traffic on the permeable base. But it is kept as low as possible, and the layer is paved over ASAP. WI Practice has been discontinued.

Agency Survey Responses 119   Q13 – Please indicate the method(s) used to prevent clogging of the permeable base layer during service. State Filter layers are not used A standard gradation for aggregate filter layers is utilized Aggregate filter layer particle size and gradation are determined A standard geotextile fabric is utilized Piping resistance of geotextile selected based on soil gradation Clogging resistance of geotextile selected based on soil gradation Other Totals 10 8 2 20 2 5 0 AL ü AR ü CA ü ü CO ü CT ü DE ü ü FL ü ID ü IL ü IN ü IA ü KS ü LA ü ME ü ü MD ü MA ü MI ü ü MN ü MS MO ü MT ü ü NE ü NV ü ü ü NJ ü NY ü NC ü ND ü OK ü ü ü OR ü PA ü SC ü SD ü TN ü TX ü UT ü VA ü WA ü ü WI ü Additional Comments/Clarifications: State Response CT We do use filter layers in the context of subsurface drainage, but we do not design pavements with permeable base layers. IL Dense-graded aggregate separation layer was used on some experimental sections. IN We are using aggregate and geotextile for separation. ME Filter fabrics are sometimes used to prevent migration of fines into the subbase. They are used as needed. MI A thin dense-graded aggregate layer is also allowed between the permeable base layer and the sand subbase. It is rarely utilized. OR Woven fabric is used under all bases placed on soil. In areas near groundwater, nonwoven fabric is used. SC Filter fabrics are typically used in the rare occurrences of drainage layer usage. WA Where the occasional permeable layer has been used, a geotextile was used for separation. WI Practice of a permeable base has been discontinued.

120 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q14 – Please indicate the method(s) used to install longitudinal edge drains to drain water away or to lower the water table. State Longitudinal edge drains are not used Installed during new construction prior to final surfacing Installed during new construction after final surfacing May be retrofitted into existing pavements Were previously used but have been discontinued due to maintenance issues Other Totals 2 29 6 24 3 1 AL ü ü AR ü CA ü ü CO ü ü CT ü ü DE ü ü FL ü ü ID IL ü ü ü IN ü ü IA ü ü ü KS ü ü LA ü ME ü MD ü ü MA ü ü MI ü ü ü MN ü ü MS MO ü ü MT ü ü NE ü ü ü NV ü NJ ü ü NY ü ü NC ü ND ü OK ü ü ü OR ü PA ü ü SC ü SD ü ü TN ü TX ü UT ü ü VA ü ü WA WI ü ü Other: State Response WI Longitudinal edge drains have been used with less frequency due to maintenance and performance issues. Additional Comments/Clarifications: State Response AL Longitudinal edge drains are only used when permeable bases are specified. DE We are working toward discontinuing edge drains as they have not been historically maintained. FL Longitudinal edge drains are used on all concrete pavements in Florida, per Standard. For asphalt pavements, longitudinal edge drains are only used in areas where high groundwater creates issues with the pavement structure. ID This would typically be limited to a short section of critical need within a roadway project. Specific details would be established by the engineer. IL The underdrain can be installed before or after PCC paving. There must be a minimum of 9½ in. of HMA before the underdrain can be installed. MA Permeable base layers were constructed on a prior demonstration project, wrapped in a geotextile filter fabric and constructed prior to paving, but are not currently utilized except under porous pavements. OR For concrete pavement only; only used in cut areas, in areas of known water issues, and for tying into existing edge drains. Draining outside slopes to ditches is preferred. TX Old rigid pavements with flexible pavement shoulders considered for rubblization projects. WA Longitudinal edge drains have been used in cut sections where there is no ditch. Overall, there has been minimal use in WSDOT. WI Practice of a permeable base has been discontinued.

Agency Survey Responses 121   Q15 – Please indicate if performance studies of drained pavements have been conducted. State Have not been conducted Have been conducted and published reports are available Have been conducted and published reports are not yet available Have been conducted and utilized to establish life expectancies Have been conducted and utilized to establish design costs Have been conducted and utilized to establish construction costs Have been conducted and utilized to establish maintenance costs Other Totals 27 8 0 2 1 0 0 0 AL ü AR ü CA ü ü CO ü CT ü DE ü FL ü ID ü IL ü IN ü IA ü KS ü LA ü ME ü MD ü MA ü MI ü MN ü MS MO ü MT ü NE ü NV ü ü NJ ü NY ü NC ü ND ü OK ü OR ü PA ü SC ü SD ü TN ü TX UT ü VA ü WA ü WI ü Additional Comments/Clarifications: State Response FL A performance life study was done in 2013 of all interstate concrete pavements, with the life of well-drained concrete pavements averaged separately. All interstate concrete pavements averaged 17 years to initial rehab, and well-drained pavements averaged 25 years. Well-drained was defined as either initial edge drains or special select embankments. IL https://idot.illinois.gov/Assets/uploads/files/Transportation-System/Research/Physical-Research-Reports/147.pdf. LA https://www.ltrc.lsu.edu/pdf/2008/Report%20117.pdf. https://www.ltrc.lsu.edu/pdf/2008/Report%20073.pdf. https://www.ltrc.lsu.edu/pdf/2009/fr_429.pdf. ME In the past the subgrade design was established and reported on. Current practice is based on those studies, and AASHTO’s recommendations. NY 1970 - Edge Drain Installation 1989 - Use of Open-Graded Subbase TX A substantial concern has existed over the maintainability of the internal drainage systems, including clogging of edge drains through rodent activity or sedimentation, crushing of edge drains, etc. VA VTRC Report 05-R35 Effect of Subsurface Drainage on the Structural Capacity of Flexible Pavement. WA Drainage problems are not generally an issue for WSDOT.

122 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q16 – Please indicate how the expected service lives of drained pavements compare to undrained pavements. State Compared to undrained asphalt pavement, drained asphalt pavements are: Compared to undrained concrete pavement, drained concrete pavements are: Other not expected to have a longer service life to first rehab expected to have a 1-10% longer service life to first rehab expected to have an 11-20% longer service life to first rehab expected to have a 21-30% longer service life to first rehab expected to have a >30% longer service life to first rehab not expected to have a longer service life to first rehab expected to have a 1-10% longer service life to first rehab expected to have an 11-20% longer service life to first rehab expected to have a 21-30% longer service life to first rehab expected to have a >30% longer service life to first rehab Totals 10 3 1 1 4 9 2 0 3 2 14 AL ü ü AR CA ü CO CT ü DE FL ID ü IL ü IN ü ü IA ü ü KS ü ü LA ü ME ü MD ü ü MA ü ü ü MI ü MN ü ü MS MO ü MT ü NE ü ü NV ü ü NJ ü ü NY ü ü NC ü ND OK OR ü PA ü SC ü ü SD ü TN ü ü TX ü ü ü UT ü ü VA ü WA ü ü WI ü

Agency Survey Responses 123   Q16 (Cont.) – Please indicate how the expected service lives of drained pavements compare to undrained pavements. Other: State Response CA Not compared. ID We've not explored this in sufficient detail to quantify our answers above. IL Cost of underdrains is assumed to be equal for both pavement types and is excluded from life-cycle cost analysis. LA Not aware of the statistics for service life benefit. Expected to have longer service life, but don't have the numbers. MA This may be project-specific and related to overall drainage factors. MI We have not quantified the amount. MO We have not quantified it as a percentage of design life. MT We have not tried to quantify a longer service life comparing a drained vs. undrained pavement section. NC For both asphalt and concrete, life extension has not been quantified. OR Curb and gutter streets typically are not drained, but over-excavation of soft soils and added sub-base help offset lack of drainage. PA Unable to determine service life extensions related to drained pavements. SD We do not take undrained versus drained pavement sections into account when performing our life-cycle cost analyses. TX Considered just to meet the design life. VA VDOT does not use drainage as part of life-cycle cost analysis. Additional Comments/Clarifications: State Response CO We have not looked at a performance life impact on pavements to my knowledge. DE We do not have an established expected service life. FL FDOT does not use drained asphalt pavement (no permeable base layers). ME Maine DOT does not do LCAs. The longer life service is based on local knowledge. NY From our Comprehensive Pavement Design Manual: Pavement drainage is critical to pavement performance. The NCHRP Synthesis 239, Pavement Subsurface Drainage Systems, states that based on a national survey, drained and maintained pavements last up to twice as long as undrained pavements. It also found that maintenance and overlays do not greatly improve the life of pavements that do not have good subsurface drainage. WA Data is not available to make an accurate assessment.

124 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q17 – Please indicate the method(s) used to monitor subsurface drainage components. State Inspections are not conducted Visual inspections of outlets/headwalls conducted at: Probing of drainage pipes/conduits to confirm no blocking exists conducted at: On an annual basis At 2- to 3-year intervals At 4– to 5-year intervals At intervals >5 years On an annual basis At 2- to 3-year intervals At 4- to 5-year intervals At intervals >5 years Totals 13 10 3 1 4 1 1 3 5 AL ü AR CA ü CO ü CT DE FL ü ID ü ü IL ü IN ü ü IA ü KS ü ü LA ü ME ü ü MD ü MA ü ü MI MN ü ü MS ü MO MT ü NE ü NV ü ü NJ ü NY ü NC ü ND ü OK ü OR ü PA ü ü SC ü SD ü ü TN ü ü TX UT ü VA WA ü WI ü

Agency Survey Responses 125   Q17 (Cont.) – Please indicate the method(s) used to monitor subsurface drainage components. State Camera inspections of drainage pipes/outlets to confirm that no blocking or collapse exists are conducted: Water flow testing to confirm that water flows from pavement surface to transverse outlets is conducted: Other On an annual basis At 2- to 3-year intervals At 4- to 5-year intervals At intervals >5 years On an annual basis At 2- to 3-year intervals At 4- to 5-year intervals At intervals >5 years Totals 0 1 0 9 0 0 1 4 3 AL AR ü CA CO CT DE FL ID ü IL IN IA KS ü LA ü ME ü ü MD MA ü ü MI ü MN ü MS MO ü MT NE NV ü ü NJ ü NY NC ND OK OR PA ü SC SD ü ü TN TX UT VA ü WA WI

126 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q17 (Cont.) – Please indicate the method(s) used to monitor subsurface drainage components. Other: State Response MI We require video inspection before paving to ensure that pipe has not been crushed from construction equipment/compaction efforts. Inspections of existing pipe may be conducted prior to a project to see if it can be reused or needs to be cleaned. MO We mandate video inspection of a minimum of 10% of the lateral and longitudinal pipe. Beyond that, we have no formal maintenance video monitoring of underdrain pipes. VA Inspection, visual and camera, are performed by the contractor after installation of the system prior to acceptance. Future inspections are identified on an as-needed basis. Additional Comments/Clarifications: State Response AR Maintenance Manual requires inspection of a minimum of 10% of the underdrains with video equipment every 2 years. Also, contracts require inspection of 100% of the underdrains with video equipment on the 10th year of service. Inspection of headwalls and rodent screens are performed on an irregular schedule and/or as needed. CT Most of the inspections occur on an as-needed basis or as part of the evaluation of existing facilities when initiating a rehabilitation project. DE Conducted on an as-needed basis. ID We have no inventory of these systems. Inspections, probing, camera inspections are established by the local maintenance foreman and the district maintenance engineer. IL District operations forces inspect outlets/headwalls regularly. Other inspections are done on an as-needed basis. IN Outlets are inspected and cleaned annually. There is no schedule for video inspection of the drains themselves, but they are done on an as-needed basis. ME Drainage structures are inspected periodically but I am not certain of the frequency for the various types of drainage structures. MS Our maintenance condition surveys are conducted over 2,800 1/10th mile sections annually. In those inspections, if edge drain headwalls are present, the functioning and maintenance of the structure is assessed. The edge drain is deemed deficient if (1) the pipe is blocked or filled with sediment or debris for more than half of its diameter, (2) the end of the pipe or concrete pad is sufficiently damaged to weaken its structural integrity, or (3) the flow capacity of the outflow is impeded by external obstruction such as sediment, rocks, vegetation, or debris. The segment evaluated is assigned an overall percent failed for these structures. MT Some informal inspections are performed by our maintenance staff, but it does not occur very often. NY We do have a special specification for underdrain video inspection (Item 605.99000017). PA Pub. 242 Pavement Policy Manual Chapter 2.3. Design Manual 2 Chapter 10.3.D Pavement Base Drains. http://www.dot.state.pa.us/public/pubsforms/Publications/PUB%2013M/May%202020%20Change%20No.%205.pdf. http://www.dot.state.pa.us/public/PubsForms/Publications/PUB%20242.pdf. http://www.dot.state.pa.us/public/PubsForms/Publications/Pub%2072M/72M_2010_7/72M_2010_7.pdf. Pub 72M Roadway Construction Standards, RC-30M. SD Very sporadic, depending on location. Some are checked annually and some at intervals greater than 5 years. TX Inspections are conducted to investigate localized pavement failures.

Agency Survey Responses 127   Q18 – Please indicate the method(s) used to identify locations of transverse outlets. State Transverse outlets not used No location markers used Paint marks applied on pavement edge/shoulder Delineator posts adjacent to the outlets Other Totals 6 16 7 15 2 AL ü AR ü CA ü ü CO ü ü CT ü DE ü FL ü ID ü IL ü IN ü IA ü KS ü LA ü ME ü MD ü MA ü ü MI ü ü ü ü MN ü MS ü MO ü MT ü NE ü NV ü NJ ü NY ü NC ü ND ü ü OK ü OR ü PA ü SC ü SD ü ü TN ü TX ü UT ü VA ü WA ü WI ü Other: State Response MI ½-in. deep, 4-in. by 6-in. depressions in the shoulder adjacent to outlet locations are required when the pavement is reconstructed or resurfaced. ND Outlet locations have an "O" cast into the concrete pavement. Additional Comments/Clarifications: State Response CO Outlets have been marked in some cases; in others they have not. DE We have recently incorporated a standard to add delineator posts adjacent to outlets. Previously, outlets were unmarked, and we found that many were damaged/destroyed during mowing operations. ID Specifics are set at the project level. We don't have standard criteria. IN Outlet locations are inventoried and stored in our GIS system. MO Since the headwalls are technically “traversable” by design, we don't feel the need to use delineators, which would likely get run over by the first maintenance mower. NY We have eliminated the use of precast headwalls for the outlets. They do not perform well in the field and are often removed by maintenance crews. TX Headwalls are not used.

128 Subsurface Drainage Practices in Pavement Design, Construction, and Maintenance Q19 – Please indicate any problem(s) observed with subsurface drainage components. State Transverse outlet pipes collapsed Longitudinal drainage pipes collapsed Transverse outlets/headwalls buried Transverse outlets/headwalls damaged or missing Transverse outlets/headwalls missing rodent screens Other Totals 27 19 32 28 27 0 AL ü ü ü AR ü ü ü ü ü CA ü ü ü CO ü ü ü ü ü CT ü ü ü ü ü DE ü ü ü ü ü FL ü ü ü ü ü ID ü ü ü ü ü IL ü ü ü IN ü ü ü ü ü IA ü ü ü KS ü ü ü ü LA ü ü ü ü ü ME ü ü ü ü MD ü ü ü ü ü MA ü ü ü MI ü ü ü ü MN ü ü ü MS ü ü ü ü MO ü ü ü MT ü ü ü NE ü ü ü ü ü NV ü ü ü ü NJ ü ü ü ü NY ü ü ü NC ü ü ü ü ND ü ü ü OK OR PA ü ü ü ü ü SC SD ü ü ü ü ü TN ü ü ü ü TX ü ü ü ü ü UT VA ü ü ü WA ü WI ü ü Additional Comments/Clarifications: State Response CO Longitudinal drainage pipes destroyed by mowing equipment. IA Our new outlet design includes a concrete headwall but does not include rodent screens because of the formation of tufa (calcium carbonate) on the rodent screen and blockage of the water flow from the outlet. MI Transverse outlets plugged with debris. MDOT is considering moving to no rodent screens to limit plugging of outlets. OR Unknown. SC None documented to my knowledge. UT No problems observed. WA Outlet pipes are sometimes difficult to find.

Agency Survey Responses 129   Q20 – Please indicate the method(s) used to evaluate the influence of subsurface drainage on the functional and structural capacity of the pavement system. State No evaluations conducted Visual distress surveys to identify moisture- related distress Visual surveys of water flow to assess functionality Falling weight deflectometer testing to assess structural capacity Impact echo testing to assess structural capacity Falling weight deflectometer testing to assess uniformity of support Impact echo testing to assess uniformity of support Ground- penetrating radar testing to assess uniformity of support Other Totals 22 15 7 12 0 6 0 3 1 AL ü ü ü AR CA ü ü ü ü ü CO ü CT ü DE ü FL ID ü IL ü ü ü ü IN ü ü ü IA ü KS ü LA ü ME ü ü ü ü ü ü MD ü MA ü ü MI ü ü MN ü ü MS MO ü MT ü ü ü NE ü NV ü NJ ü NY ü ü ü ü ü NC ü ND ü OK ü OR PA ü ü ü SC ü SD ü ü ü ü TN ü TX ü UT ü VA ü ü ü WA ü WI ü Other: State Response ME GPR testing method for pavement structural analysis is being developed. Additional Comments/Clarifications: State Response AL FWD testing is performed on most projects regardless of the existence of subsurface drainage. DE We have one major corridor where we utilized highway-speed FWD testing to determine the extent of a pavement failure due to the underdrains failing and the pervious pavement layer failing. FL Visual surveys of outlet conditions are made on a regular basis. OR Several sections of CRCP in cuts with edge drains or flat undrained areas have performed worse than CRCP on embankments or with deep ditches. Localized underground springs have caused several documented localized early failures in asphalt pavements. VA VDOT uses visual surveys of pavements to identify areas of potential subsurface moisture issues, which may or may not be in conjunction with subsurface drainage features. In addition, FWD testing may be used to assess the influence of moisture on pavement structures. Recently, VDOT has been using GPR to identify anomalies within a pavement section and identify coring/boring locations to aid in identifying pavement issues such as those associated with moisture.

Abbreviations and acronyms used without denitions in TRB publications: A4A Airlines for America AAAE American Association of Airport Executives AASHO American Association of State Highway Officials AASHTO American Association of State Highway and Transportation Officials ACI–NA Airports Council International–North America ACRP Airport Cooperative Research Program ADA Americans with Disabilities Act APTA American Public Transportation Association ASCE American Society of Civil Engineers ASME American Society of Mechanical Engineers ASTM American Society for Testing and Materials ATA American Trucking Associations CTAA Community Transportation Association of America CTBSSP Commercial Truck and Bus Safety Synthesis Program DHS Department of Homeland Security DOE Department of Energy EPA Environmental Protection Agency FAA Federal Aviation Administration FAST Fixing America’s Surface Transportation Act (2015) FHWA Federal Highway Administration FMCSA Federal Motor Carrier Safety Administration FRA Federal Railroad Administration FTA Federal Transit Administration GHSA Governors Highway Safety Association HMCRP Hazardous Materials Cooperative Research Program IEEE Institute of Electrical and Electronics Engineers ISTEA Intermodal Surface Transportation Efficiency Act of 1991 ITE Institute of Transportation Engineers MAP-21 Moving Ahead for Progress in the 21st Century Act (2012) NASA National Aeronautics and Space Administration NASAO National Association of State Aviation Officials NCFRP National Cooperative Freight Research Program NCHRP National Cooperative Highway Research Program NHTSA National Highway Traffic Safety Administration NTSB National Transportation Safety Board PHMSA Pipeline and Hazardous Materials Safety Administration RITA Research and Innovative Technology Administration SAE Society of Automotive Engineers SAFETEA-LU Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (2005) TCRP Transit Cooperative Research Program TDC Transit Development Corporation TEA-21 Transportation Equity Act for the 21st Century (1998) TRB Transportation Research Board TSA Transportation Security Administration U.S. DOT United States Department of Transportation

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