Public Street Standards
D~~~E
~<Æ~
MEMORANDUM
July 12, 2004
TO:
The Honorable Mayor and City Council Members
FROM:
Michael C. Van Milligen, City Manager
SUBJECT: Public Street Standards
Acting Public Works Director/City Engineer Gus Psihoyos is providing information on
the City's specifications and standards for minimum thickness and composition for
asphalt and concrete surfaces. Within 90 days the Engineering Division will review and
provide recommendations.
fìLJJ í:~ ¿
Michael C. Van Milligen
MCVM/jh
Attachment
cc: Barry Lindahl, Corporation Counsel
Cindy Steinhauser, Assistant City Manager
Gus Psihoyos, Acting Public Works Director/City Engineer
¡ 0 °C¡ \\'<J C! ""'¡riD
D~
~ck~
MEMORANDUM
July 12, 2004
FROM:
Michael C. Van Milligen, City Manager
Gus Psihoyos, Acting Public Works Director ~Q
TO:
SUBJECT:
Public Street Standards
INTRODUCTION
On June 21, 2004, the City Council approved the preliminary plat for Paradise Hills 2nd
Addition without the street standard waiver. In this approval process, the developers
(Roger and Lois Schueller) requested two private streets to be built with 4 inches of
asphalt over 14 inches of base stone (original request was for 2 inches of asphalt over 6
inches of base stone). With the vote of 4-3, City Council approved the preliminary plat
for Paradise Hills 2n Addition without the street standard waiver (7 inches of asphalt
over 4-1/2 inches of base stone).
During Council discussion, Engineering indicated it would review the asphalt pavement
thickness standards proposed by the Center for Transportation Research and Education
(CTRE). CTRE, the focal point for transportation at Iowa State University, performs
transportation research for public and private agencies and companies, manages its
own education program for transportation students, and conducts local, regional, and
national transportation services and continuing education programs.
DISCUSSION
Exhibit A provides a comparative analysis of minimum asphalt thickness and
composition among the: the City of Dubuque; CTRE (as noted in its Statewide Urban
Design and Specifications (SUDAS) manuals; and the American Association of State
Highway & Transportation Officers (AASHTO).
The SUDAS Hot Mix Asphalt (HMA) Committee is currently reviewing the applicable
SUDAS design and specifications (6" base with 8" asphalt). Since most pavements are
constructed with a granular subbase, the Committee recommended that if 6" or more of
crushed stone subbase is used, the total depth of the HMA may be reduced by 2".
Therefore, if 6" of crushed stone base is used, the total depth of the HMA for local
residential streets may be reduced to 6". This recommendation has not been approved
and will be presented to the District Committees and the Board of Directors in the near
future. (See attached e-mail from Larry Stevens, SUDAS Director.)
As Larry Stevens noted in the attached e-mail, the City of Dubuque standards are
comparable to the standard asphalt thickness recommended by SUDAS.
Exhibit B provides a comparative analysis of asphalt and base thickness standards in
major tri-state cities. As noted, base thickness varies from 0" to 10", while asphalt
thickness varies from 3" to 9".
RECOMMENDATION
The Engineering Division within the 90 days will review and provide recommendations
to the City Council for both the City's specifications and standards for minimum
thickness and composition for asphalt and concrete surfaces.
Page I of I
From: Larry Stevens [Istevens@iastate.edu]
Sent: Friday, July 09,20041 :15 PM
To: gpsihoyo@cityofdubuque.org
Cc: brich@iastate.edu: pcconc@iastate.edu
Subject: Asphalt Paving depths
Gus,
Per our discussion this morning, the SUDAS hot mix asphalt depth requirement for local residential
streets is 6" of basel intermediate and 2" of surface, for a total thickness of 8". This thickness is based on
placement on a uniform natural subgrade.
The SUDAS Hot Mix Asphalt Committee is currently reviewing the applicable SUDAS design and
specifications. Since most pavements are constructed with a granular subbase, the Committee
recommended that if 6" or more of crushed stone subbase is used the total depth of the HMA maybe
reduced by 2". Therefore, if6" of crushed stone base is used the total depth of the HMA for local
residential streets may be reduced to 6". This recommendation has not been approved and will be
presented to the District Committees and the Board of Directors in the future.
It is my understanding that Dubuque's standard is 7" ofHMA over 4 1/2 inches of stone base. On an
equivalent strength basis, this would be approximately equal to the current SUDAS requirement of 8" of
HMA on natural sub grade and the 6" stone with 6" HMA recommended by the HMA Committee.
If you need any additional information, feel free to contact me.
Larry
Larry Stevens
SUDAS Director
Center for Transportation Research & Education
2901 S. Loop Drive, Snite 3100
Ames,]A 50010-8632
Phone: (515) 294-0419
Fax: (515) 294-0467
Email: lstevens@íastate.edu
WWJI'.ÍQ"W.asuc!:lS.org
07/09/2004
EXHIBIT A
MINIMUM ASPHALT THICKNESS & COMPOSITION FOR STREETS
CITY OF DUBUQUE CTRE AASHTO
Street Base* Asphalt Structural Base* Asphalt Structural Base* Asphalt Structural
Classification No. (SN)** No. (SN)** No. (SN\**
Local 4.5" 7" 3.71 6" 8" 4.36 14" 4" 3.72
Current
I 6" 6" 3.48 t I
Proposed
Base: Crushed (Graded) Stone
Structural Number: Strength per Inch of Asphalt. There is an indefinite number of combinations of base stone to
asphalt thickness; key factors for base/asphalt thickness are the subbase (soil) stability and constructability (the
minimum thickness of base stone to sustain construction traffic). The greater the structural number, the greater the
strength of the composite roadway. Expense increases as the asphalt thickness increases.
EXHIBIT B
Pavement
Comoarison Base Thickness ACC Thickness
Ames 0 9
Cedar Rapids 6 8
Champaign 0 9
Des Moines 0 8
Dubuque 4.5 7
Madison 10 3.25
Rockford 3 8
Sioux City 6 8
Waterloo 4 7.5
LaCrosse 6 3
Iowa Standard 0 8
12
10
j 8
6/20/2003
ASPHALT PAVEMENT COMPARISON CHART BY CITY
Local Street Standards
16
14
4
0
,{þ.11' >.~ 0"",0,p',.1>.§:'1 00..,0.1>
~~ q!'<' Q" ~èf' ff'" I§' ",,0 ~(j ¡¡fÞ~ .tY' ~If
.t>~ ,<!-of fA' <:/, ~" q;.<f c;,"f' ~ 'v<iP <iJ!i'
if (j <J ,.¡'I>
Average Structural Number 4.37
Dubuque Structural Number 3.62