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HomeMy WebLinkAboutA001 - Council Action Form dated March 24, 1992 COUNCIL ACTION FORM Item # C Date: March 24, 1992 SUBJECT: Establishing new street construction standards. BACKGROUND: Last fall staff presented a proposal for upgrading the street thickness standards so that the pavement breakup problems that we have been experiencing will be lessened. The proposal called for various changes in the street design widths and thicknesses based on expected traffic genera- tion over the life of the pavement structure. The changes are summarized on the attached staff report. Following the presentation to Council, the development community was informed of the proposals and asked to comment. One detailed comment was received from an area consulting firm and was responded to with respect to technical analysis of the pavement design process. No other comments were received. In addition, a meeting was held to further dis- cuss the proposals. Developers, engineers, and business representatives were invited. Two developers attended the meeting to discuss the stan- dards. Their concern related to the increased cost that would be passed on to the property buyer. Staff pointed out that the increased first cost for the street would eventually be offset by the reduction in long term maintenance costs. Implementation of these proposals mean increased costs on the front-end stages but will result in longer street pavement life with less long term maintenance costs. It should be noted that these costs for street con- struction should not put the Ames development community at a disadvan- tage, since the new standards are similar to other community standards around the state. If traffic volumes require additional width or pavement thickness to meet the needs of the community as a whole, in addition to meeting the require- ments of the surrounding development, the City will pay those extra costs as is the current policy. The proposed changes, if accepted, should take the form of an amendment to the subdivision ordinance. ALTERNATIVES: 1. Approve an ordinance adopting the proposed street design standards, to be effective for any construction that involves development of Administrative Plats filed after the subdivision ordinance is amended. 2. Reject the new street design standards and continue to expect addi- tional short term short maintenance cost increases. MANAGER'S RECOMMENDED ACTION: It is recommended by the City Manager that the City Council adopt the new street standards and begin implementation on any development project that files an Administrative Plat after the subdivision ordinance is amend- ed. COUNCII. ACTION• PW:Revl STREET DESIGN STANDARDS Over the past couple of years the staff has been considering our street design standards with respect to street width, thickness of pavement, presence of on-street parking, and city payment for extra width and extra thickness. The concern over the standards relates to the exten- sive pavement problems that are accelerating around the community. One of the problems that accelerate pavement breakup is excess water in the pavement and the subgrade under the pavement. Current technolo- gy calls for controlling the water by installing a granular (sand) subbase and tile drains to remove the water from the pavement area. If this construction technique is employed, the pavement life is extended considerably. With any change in design standards, a change in costs will be forth- coming. Several philosophies must be balanced as the costs of street construction are evaluated. The first relates to evaluating which should be the main point of emphasis, the first cost as the street is constructed or the long term maintenance costs. Higher design standards will result in higher first costs and lower long term maintenance. Lower standards result in lower costs initially and higher maintenance and rehabilitation costs. This is the proverbial "Pay me now or pay me later" philosophy. It is important to evaluate the design standards to provide a sufficient pavement structure to meet the needs of the street. It is also important to note that the design standards have to remain relatively competitive with area communities so that the development community is not placed at a cost disadvantage. The more stringent the standards are, the higher the unit cost of development. Currently the City's standards involve the following: 1. Local streets with daily traffic less than 750 vehicles. Width - 27' to 31' Thickness - Asphalt = 7" Concrete = 6" No subbase or subdrains required. Parking allowed one side. 2. Local streets with daily traffic between 750 and 2,000 vehicles. Width - 31' to 39' Thickness - Asphalt = 7" Concrete = 6" No subbase or subdrains required. Parking allowed on one side if 31' wide; two sides if 39' wide. - 1 - 3. Collector streets with traffic between 2,000 and 5,000 vehicles per day. Width - 31' to 45' Thickness - Asphalt = 7" Concrete = 6" No subbase or subdrains required. Parking dependent on volumes/width combinations. 4. Collector streets with traffic between 5,000 and 10,000 vehicles per day. Width - 45' to 49' Thickness - Asphalt = 8" Concrete = 7" No subbase or subdrains required. No parking allowed. 5. Arterial streets with daily traffic above 10,000 vehicles. Width - 45' to 70' (left turn lanes) Thickness - Asphalt - 9" Concrete - 8" Subbase and subdrains required. No parking allowed. The above standards are modified for Cy-Ride routes no matter what the street classification. Thickness is 9" of asphalt and 8" of concrete with subdrains and subbase required. For street construction in new subdivisions, the City has paid for extra width above that which is needed for the development (31' for residential areas and 41' for commercial areas). In addition, the City has negotiat- ed with developers for construction of off-site improvements that gener- ally has resulted in 50-50 cost sharing arrangements. In order to determine what other Iowa communities were using as stan- dards, a survey was completed. Fifteen cities were identified with 12 returning their surveys. The cities responding included Bettendorf, Davenport, Council Bluffs, Cedar Rapids, Iowa City, Sioux City, Marion, Ankeny, Des Moines, Clinton, Marshalltown, and West Des Moines. The survey information is summarized as follows: 1. Local streets with less than 750 ADT (Average Daily Traffic). a. Width. The width varied from 25' to 31' with 31' being the most utilized width. b. Thickness. Asphalt. Thickness varied from 7" to 9111 with 8" required most often. Concrete. Thickness varied from 6" to 7" with equal numbers of cities using each. - 2 - C. Subbase and Subdrains. Three cities required subbase and subdrains; one required subbase only; one required subdrains if wet conditions existed; and 7 did not have any requirements for subdrains or subbase. d. Parking. Three allowed parking only on one side and nine allowed it on both sides. Summary In the surveyed cities, the most frequent responses were: Width is 31' with either 8" asphalt or 6" or 7" concrete with no subdrains or subbase and parking is allowed on both sides. 2. Local streets with traffic between 750 and 2,000 ADT. a. Width. Varied from 26' to 35' with most cities requiring 311. b. Thickness. Asphalt. Varied from 7" to 91" with most cities requiring 811. Concrete. Equally split between 6" and 7" C. Subbase and Subdrains. Exactly the same as for local streets with less than 750 ADT. d. Parking. Five allowed parking on one side with seven allowing it on both sides. Summary In the surveyed cities, the most frequent responses were: Width is 31' with either 8" of asphalt or 6" or 7" of concrete with no subdrains or subbase and parking is allowed on both sides. 3. Collector street with traffic volumes between 2,000 and 5,000 vehicles per day. a. Width. Varied from 28' to 45' with 31' and 41' wide being re- quired by the most cities. b. Thickness. Asphalt. Varied from 7" to 12" with 91" being the most frequent requirement. Concrete. Varied from 6" to 9" with 7" to 8" the usual thickness. c. Subbase and Subdrains. Exactly the same as for local streets. d. Parking. Five cities allowed parking on one side and five cities allowed parking on both sides. Three cities did not allow any parking. 3 - s Summary In the surveyed cities, the most frequent responses were: Width is either 31' to 41' wide with 9,j" asphalt or 7" or 8" concrete. The amount of parking varied depending on the width and traffic volume combinations. No subbase or subdrains required. 4. Collector streets with traffic greater than 5,000 but less than 10,000 ADT. a. Width. Varied between 31' and 53". b. Thickness. Asphalt. Varied from 6" to 9Z" with 8" being the most frequent requirement. Concrete. Varied from 7" to 10" with 7" being the thick- ness most often required. c. Subbase and Subdrains. Four cities did not require anything while five required both subbase and subdrains. One city required subdrains if the area was wet. Two cities did not answer. d. Parking. Seven cities did not allow parking while two allowed it on one side and three allowed parking on both sides. Summary In the surveyed cities, the most frequent responses were: Width is 45' wide with an asphalt thickness of 8" or a concrete thickness of 711. Subdrains and subbases are most often required. Parking is not allowed. 5. Arterial streets with traffic volumes greater than 10,000 vehicles per day. a. Width. Varied from 37' to 70' with 45' or 49' being required by most cities. b. Thickness. Asphalt. Varied from 8" to 13" with 9" being the most often required. Concrete. Varied from 71" to 10" with 8" required by most cities. c. Subbase and Subdrains. Required by 7 cities, subbase only required by one city with two not requiring any special treat- ment. Two cities did not answer. d. Parking. Not allowed by any of the cities. Summary In the surveyed cities, the most frequent responses were: Width is either 45' or 49' wide with 9" of asphalt or 8" of concrete. Subbase and subdrains are required and no parking is allowed. - 4 - With respect to extra width and thickness, all cities paid for extra width over their standard residential or commercial street as appropriate. All but two cities paid for extra depth over that required by the development. Comparing the City of Ames' design standards to the consensus of the other community standards indicates that our pavement structure is not as thick in the three street classifications involving traffic less than 5,000 vehicles per day. In addition, it is apparent that most cities are installing subbase rock and subdrains on collector streets with traffic volumes be- tween 5,000 and 10,000 vehicles. Examining the differences between the state consensus and the city's standards would lead to the conclusion that we should be experiencing problems with our higher volume (750 to 2,000 vehicles per day) local streets and the collector streets. In reality, this is where we do face our most urgent need for major maintenance and rehabilitation. It is important to note that our current design standard are not providing a twenty year life prior to major rehabilitation. The twenty year life is the minimum that should be expected. With the above information, it is important to evaluate the street design standards. Based on extending the pavement life before major maintenance or rehabilitation is needed, a review was completed using the American Association of State Highway and Transportation Officials (AASHTO) stan- dards, which are the industry standards. The following changes are recommended: 1. Local streets ADT<750 Add 1" of asphalt thickness to 8" from the current 7" or z" of con- crete thickness to 61" from the current 6". 2. Local streets 750> ADT <2,000 Add 2" of asphalt thickness to 9" from the current 7" or 1" of con- crete thickness to 7" from the current 6". 3. Collector street 2,000> ADT <5,000 a. Add 2"' of asphalt thickness to 9"' from the current 7" or I"' concrete thickness to 72" from the current 6". b. Require subbase and subdrains if water and soil conditions indicate. 4. Collector streets 5,000 ADT <10,000 a. Add 2" of asphalt to 10" from the current 8" or 1" of concrete to 8" from the current 7". b. Require subbase and subdrains. 5. Arterial streets ADT >10,000 Add 2" of asphalt to 11" from the current 9" or 1" of concrete to 9" from the current 811. 5 - Implementation of these changes would mean that the development communi- ty could pay increased street construction costs. As an average, this additional cost could be $500 per lot based on the proposed local street standards and lots with 80' frontage. It must be noted however, that these costs will not put the development community at a disadvantage since the new standards would be similar to other community standards around the state. For streets with projected traffic volumes of less than 750 vehicles per day, no additional costs would be seen. The narrower 27' street, although with thicker pavement, does not cost any more than the old 31' width standard. If traffic volumes require additional width or pavement thickness to be built, the City has paid these costs. As noted earlier, the consensus across the state is that communities do pick up costs for extra thickness required. Extra width requirements are not proposed to change. At the present time the street width standards are appropriate. Costs for the extra width would stay the same as currently experienced. If streets are designated as bus routes, the pavement design is developed using arterial street standards no matter what the street would ordinarily be classified. This extra cost totals approximately $23,000 for a 500 foot length of street. The cost of this extra requirement has been paid for by the City. Discussions with Cy-Ride officials have begun to determine if smaller buses can be utilized on some of the routes to limit the amount of street that needs to be built to higher standards. - 6 -