1. Reducing Engineering standards: GOOD OR Bad?
AASHTO Subcommittee on Design
July 14, 2008
David C. O’Hagan, PE
Florida DOT State Roadway Design Engineer
Reducing Engineering standards: GOOD OR Bad?

2. AASHTO vs ppm SITUATION FDOT Plans Preparation Manual (PPM) GOAL
AASHTO ”Greenbook”
FDOT Plans Preparation Manual (PPM)
GOAL
To reduce the cost of DOT projects without sacrificing safety and operational/functional characteristics.
ANALYSIS
DOT’s Costs: Pre-construction, right of way, construction, maintenance.
Maintenance: Insignificant differential.
User Costs: Safety
SITUATION:
Federal rule requires that the design of National Highway System roads conform to AASHTO “Greenbook” criteria, which generally provides a range of design values for various design elements. The Department’s PPM criteria implicitly places an emphasis on safety and are generally based on the high side of AASHTO ranges deemed practical for Florida conditions as observed through experience. The Executive Committee commissioned a study to evaluate the cost of using PPM criteria versus minimum AASHTO criteria.
GOAL:
As composed by the task team, the goal is to review FDOT design criteria against AASHTO requirements and determine which FDOT criteria should be revised to reduce costs without sacrificing safety and operational/functional characteristics.
ANALYSIS:
The cost of DOT’s road design criteria has 4 components – pre-construction, construction, right-of-way, and maintenance. Assuming that pre-construction costs are nearly identical despite the criteria used, our study has concluded that criteria that significantly effects cross-section width has the largest impact due to right-of-way costs impacts, followed much less significantly by construction impacts and then maintenance costs. However, reduced criteria also have potential safety impacts to our customers which are now more quantifiable and in the cases studied be of the same magnitude as right-of-way costs.

3. AASHTO VS PPM
OPTIONS
Maintain Status Quo: Use Variations Process to justify reduced criteria
Reduce PPM Criteria: Eliminates need for some Variation submittals
Revise Variation Requirements: Include a safety analysis to quantify impacts of reduced criteria.
OPTIONS:
There are three options for consideration as follows:
Maintain Status Quo: Currently, the Districts may use the Variation Process to reduce PPM criteria but stay within the AASHTO criteria minimums. This option works as demonstrated in a thorough review of two District 7 rural widening projects.
Revise PPM Criteria: By revising our published criteria, especially that which significantly reduces cross-section width, the Districts would avoid many Variations they are now documenting.
Revise Variation Requirements: Currently, a safety analysis is only required for Exceptions. Adding a safety analysis to certain Variations, gives the EOR more comfort with his assignment to use Variations to reduce project costs.

4. AASHTO VS PPM RECOMMENDATION JUSTIFICATION
Option 3: Require a safety analysis with Design Variations for all new and reconstruction projects when reductions in critical design elements are being considered.
JUSTIFICATION
Variations Process already working well.
Means to quantify safety impacts of cross-section decisions.
Consistent with including non-DOT costs in our decisions (user costs in pavement-type selection).
RECOMMENDATION:
The Task Team recommended that the Department retain current PPM criteria and revise its Variation Procedures to include a safety impact analysis for new and reconstruction (not 3R) projects. The forthcoming AASHTO Highway Safety Manual will be an excellent tool that can either be used as is or eventually calibrated to meet the FDOT’s crash data.
JUSTIFICATION:
There are quantifiable means of estimating safety impacts for most roadway design decisions. Maintaining the status quo could be viewed as the Department is making criteria decisions more based on its costs than on public safety. By revising our criteria at this time to reduce cross-section width without a safety analysis could be interpreted similarly.

5. AASHTO vs. PPM 2007 Study by Roadway Design Office
Construction Cost Differences Only
Interstate Widening (1.2%)
New Rural Freeway (8%)
New Rural Arterial (7%)
New Urban Arterial (10%)
New Overpass (21%)
In 2007, the FDOT State Roadway Design Office performed an initial investigation of the cost impacts our PPM criteria have on construction when compared to an identical project constructed using lower values from the AASHTO Greenbook.
This study, did show savings in construction costs on new construction that ranged from 7 to 21%.
However, the cost estimates obtained from the our Long Range Estimate program on these imaginary projects did not include many elements, especially right-of-way.
The study was also criticized for not looking at more typical DOT projects like widenings. .

6. AASHTO vs. PPM 2008 Study by Roadway Design Office:
Include right of way and maintenance costs with construction costs.
Rural Arterial Widening
Urban Arterial Widening
Interstate Widening
New Overpass Construction
The new Task Team met in August of last year and created a Statement of Purpose (the “Goal” stated earlier).
The team also charged the Roadway Design Office to collect actual projects from the districts and review the cost impacts of design criteria differences in the projects’ construction, right-of-way and maintenance costs.
Ideally we were hoping to review representative projects for urban and rural arterial widening as well as interstate widening and new overpass structures.
To date we have looked at two rural arterial projects.
The urban arterial projects we received were very complex and we have not yet reviewed an interstate widening project.

7. SR 43 (US 301): Balm Rd to Gibsonton Dr.
Hillsborough County, 6.16 miles
Currently: Two-lane rural
New Design: Six-lane rural with sidewalk and shared-use path.
Design at 90% Complete when studied
Several Variations to eliminate ROW acquisition for typical section
The first Rural Arterial Widening Project we investigated was SR 43 from Balm Rd. to Gibsonton Drive.
This is a 6.16 mile long project in Hillsborough Co. that is being widened from two to six lanes.
It also contains sidewalk and share-use facilities.
The plans were at 90% complete when we studied the project.
In this case, District 7 had already done several design Variations on the project to keep it within the existing right-of-way.
SRDO took these plans and created a new PPM-compliant typical sections and calculated new quantities as well as construction and ROW costs.

8. Here you see two typical sections for the project.
The one at the top is what will be constructed and the one at the bottom is what the PPM criteria normally requires.
“Clouded” items are those that differ between the two typicals and include:
Median width (22’ vs 40’) and type (depressed vs. raised).
Side Slopes 1:4 vs. 1:6.
Assuming the same facilities are provided by the sections we end up with 30’ more ROW width.

9. SR 43 (US 301): Balm Rd to Gibsonton Dr.
As designed
PPM Design
Construction: $82,200,000
Right of Way: $10,200,000
(Ponds)
DOT Costs: $92,400,000
Crash (20 yr): $95,600,000
DOT+User Costs (20 yr): $188,200,000
Construction: $82,800,000 (+0.7%)
Right of Way: $26,300,000 (+158%)
DOT Costs: $109,100,000 (+18%)
Crash (20 yr): $88,000,000 (-8%)
DOT+User Costs (20 yr): $197,300,000 (+5%)
Looking at actual cost differential we can calculate the following:
Construction costs are not that much more 0.7% but this is principally due to the increased amount of fill and curb and gutter necessary to construct the narrower raised median. This greatly lessened the impact of the increase fill from the slope steepening from 1:6 to 1:4.
ROW costs are $16.1M higher ($2.6M/mile) when using the PPM section. This is 158% higher than as designed.
Potential crash costs are an eye-opener. By constructing our normal rural median and 1:6 front slope, crash costs could have been reduced by 8%. But look at the liability to our users either way – about $750K per mile per year.
Maintenance costs for this 30’ increase in ROW were about $60K over 20 years and therefore not considered significant.
Thus, the DOT Costs on this project are expected to be about $92M but if the project had been constructed without variations, the cost would have been $109M – an 18% increase.
However factoring in user costs over 20 years, the percentage gap narrows to only 5%.

10. SR 50: US 19 TO CR 587 Hernando County, 3.73 miles
Currently: Four-lane rural
New Design: Six-lane rural with sidewalk and shared-use path.
Design at 30% Complete when studied
Several Variations to eliminate ROW acquisition for typical section
Closed conveyance drainage system
The second rural arterial widening project we reviewed is a 3.7 mile stretch of SR 50 in Hernando County. This is a widening from 4 to 6 lanes with added sidewalk and shared use facilities. The project was only at 30% when we received it for analysis. This project was selected not only because of its need for Variations, but also because the SR43 project’s construction cost differential was heavily diluted by the use of a raised median. This project was also unique as D7 was able to reduce ROW acquisition with the use of a closed drainage conveyance system which greatly reduces ditch depth (and width).

11. Here again are the two cross-section investigated
Here again are the two cross-section investigated. The top is what is currently under design and the bottom one is a more typical PPM-compliant design. Note these clouded differences in criteria:
Median width was reduced from 40’ to 30’.
Outside shoulders were reduced from 10’ to 8’ and
Front slopes were increased from 1:6 to 1:4.
Note that both sections still fit within the ROW so ROW costs do not influence this analysis (similar to the 2007 study) because both typical sections assume Closed Conveyance drainage. However, the PPM section requires numerous retaining walls to keep within the ROW. Had the fully compliant PPM section been used without both the closed conveyance drainage system and the retaining walls, the District estimated about $33M in ROW would have needed acquiring.

12. SR 50: US 19 TO CR 587 AS DESIGNED PPM DESIGN
Construction: $49,200,000
Right of Way: $0
DOT Costs: $49,200,000
Crash(20 yr): $85,600,000
DOT+User Costs (20yr): $134, 800,000
Construction Cost: $58,100,000 (+18%)
(Walls were +17%)
Right of Way: $0*
DOT Costs: $58,100,000
Crash(20 yr): $79,100,000 (- 8%)
DOT+User Costs (20yr): $137,200,000 (+2%)
* $32,800,000 if open conveyance & excluding business damages.
By reducing shoulder and median widths and increasing front slopes, District 7 was able to reduce construction costs by 18%. But $8.4M of this cost was in retaining walls that would need to be constructed adjacent to the sidewalk and shared use facilities to keep the project within the right of way – still a good decision based on the $33M cost of the ROW. The actual net cost of the additional median, shoulder and front slopes was only $500K or about 1% of the increased construction cost.
Regarding right of way, there was no difference as again D7 kept within the existing ROW. Had District 7 used our typical criteria (and not included walls), an additional $32,800,000 of ROW would have been necessary.
Using the PPM criteria, crash costs to our users are reduced by 11% from $86M to $79M. When run separately, the crash cost for the reduced median was only $500K for 20 years; and for the increased side slope was $6M. Interestingly enough, according to the HSM there is not enough information know to judge the predicted safety impact of shoulders greater than 8’. Further study is being conducted on that.
In conclusion, this analysis showed that although the District saved $8.9M in construction costs, the users over the next few years are predicted to incur $6.5M more in crash costs. The net savings in using reduced criteria on this project was about 2%.

13. SAFETY IMPACT DIFFERENCES
SR 43 (Hillsborough)
Side Slope:
HSM: +$6.6M
RSAP: +$9.4M
Median Width:
HSM: +$1.0M
DOT Research: +$3.0M
Combined:
HSM: +$7.6M
SR 50 (Hernando)
Side Slope:
HSM: +$6.0M
RSAP: +$9.7M
Median Width:
HSM: +$0.5M
DOT Research: +$0.5M
Combined:
HSM: +$6.5M
Now as most of you know, there are other safety impact estimating tools out there, chief among them the AASHTO Roadside Safety Analysis Program (RSAP).

14. Accident Modification Factors
Undivided
Divided
Of great interests to designers and planners are the table the HSM provides to show you the Accident Modification Factors for the design decisions they may be required to make , especially to stay within the ROW.
For instance….
Thus designers and engineers now have a better idea what impacts each trade-off they consider has. Up to now they have not had this ability in one document.

15. CONCLUSIONS Rural Widening: Additional Work:
Cost Savings are in ROW not construction.
Variations procedure working well.
AASHTO minimum criteria has significant safety impacts.
Recommend including typical section safety analysis in Variation process for non-3R projects.
Additional Work:
Study Urban & Interstate Widenings
Study Overpasses
Review crash data of AASHTO-only states & compare to Florida