Every year I go to my daughter’s school for the Great American Teach-In, and I explain that engineers Design, Build, Operate, and Maintain just about everything we use in our everyday lives. Then they get to “design” and “build” a marshmallow tower. They “operate”, or play, with it and it starts falling apart. Then it is time to “maintain” it… and that is where I lose them. Most people think of maintenance on anything the same way my teenager feels about cleaning her room; it is a dreaded chore. In terms of highway maintenance, we maintain asphalt pavement through milling/resurfacing and concrete pavement through sealing cracks and replacing slabs. These activities by themselves seem fairly simple and routine, like a chore. However, the Resurfacing, Restoration, and Rehabilitation (RRR) program in Florida is anything but simple.
Since asphalt was first used in the United States in the 1860’s, there has been a need to maintain and prolong its life. Most state Departments of Transportation (DOTs) have a resurfacing program. In the Federal Highway Administration document, Good Practices: Incorporating Safety into Resurfacing and Restoration projects (dated December 2006), discusses how roadway maintenance programs and safety programs are merging and provides guidance on how to do this.
The RRR process in FL starts with “extending the service life” of the pavement and even this can get complicated. Most asphalt pavements are designed for a 15 to 20 year service life and concrete pavement can last up to 30 years. But this expectancy is only if the traffic projections and equivalent single axle loads (ESALs) over the design service life match actual conditions. While more often than not, our estimates and calculations are correct, there are always those special cases when something outside our control or an unknown factor cause the service life to be significantly lower than anticipated. Let me give you just a few examples of projects I have worked on.
On SR 44 in Lake County from the County Line to SR 44.CR 468, the existing pavement was failing and severely rutted. After obtaining traffic data and looking at the current and projected ESAL values, it was determined that the existing asphalt pavement section was structurally deficient or simply not thick enough to handle increased truck traffic on the corridor. Two options to rehabilitate the roadway were reviewed, reconstruction of the entire roadway or add additional structural course to the existing pavement section and raise the profile of the road. Ultimately, adding the additional structural course was the more feasible option. Sounds simple, right? Wrong. In order to provide the required structural number for the projected ESAL data, an additional two and a half (2.5) inches of Super Pave (SP) structural course was added to the roadway. This required all the median openings to be raised and reconstructed, all of the shoulders had to be reconstructed with front slope revisions, and all the driveways had to be re-profiled.
On SR 674 in Hillsborough County, there was settlement or a depression in the roadway just east of the Carlton Branch Bridge that was causing trucks to “bottom out” and scrape the existing asphalt. Several patches or overlays were attempted in this area, but the depression continued to form over time. When it came time for the regular resurfacing of this corridor, additional core data that went deeper than typical cores was obtained. This additional core data revealed that there was an isolated pocket of clayey soil about 5 feet below the base material. Due to the heavy truck traffic on this corridor, the clayey soil were continually compressed. The simple repair would be to just dig down and remove the clayey soil, right. Unfortunately, this project was on a two lane rural roadway, with the only detour option being almost 10 miles long. The solution chosen was to strength the pavement section by installing a woven geotextile in the base material, overbuilding the structural course and raising the profile of the road.
The second part of the RRR process in Florida is to “enhance highway safety”. This starts with a thorough review of the 13 AASHTO Controlling Design Elements: design speed, lane width, shoulder width, bridge width, structural capacity, vertical clearance, grade, cross slope, superelevation, horizontal alignment, vertical alignment, stopping sight distance, and lateral offset (or clearzone). Like most states, AASHTO sets the minimum criteria and FDOT has developed more stringent standards for some of these design elements. We attempt to correct as many deficient elements as budget, schedule, and right of way will allow.
Other safety considerations on RRR projects include the following:
- Intersection operations including signalization needs, pavement markings, turning radii, channelization, and ADA needs
- Drainage concerns where there is a flooding history or potential for hydroplaning
- Pedestrian, Bicycle, and Transit needs
- At-grade railroad crossings
- Aesthetics and Landscaping
- Highway lighting
- Highway Traffic Control Devices
- Bridges and associated design elements of a bridge
- Roadway Safety Hardware such as guardrail
- Ancillary Structures associated with signs, signals, lighting and ITS
This is a lot of design elements to review. The PPM also allows for engineering judgement on when these elements should be corrected with the RRR project or can remain. To supplement the PPM and provide consistent results across the state and among the numerous consultants, FDOT has develop RRR Practical Design Guidelines which have basically develop three (3) lists; items to always correct on a RRR project, items that do not need to be corrected on a RRR project, and items that are left up to the discretion of the FDOT Project Manager. Let me give you an example of how we incorporated safety on a RRR project.
One of the most challenging resurfacing projects I have worked on was along Alternate US 19 (SR 595) from Whisper Lake Road to Harry Street in Pinellas County. This is the main thorough fare that connects the beach communities of Ozona, Palm Harbor, and Crystal Beach. It has heavy pedestrian and bicycle use and at the time of the RRR project did NOT have continuous sidewalk and bike lanes.
The main safety objectives were:
- To “fill in the gaps” in the sidewalk
- Add bicycle lanes
- Make sure all intersections were ADA compliant
- Eliminate areas of standing water that were causing hydroplaning
- Correct intersection deficiencies at DeSoto Blvd and Bee Pond Road
I use this term lightly, but let’s talk about the “easy” stuff first. Bicycle lanes were achieved by utilizing existing paved shoulders, adding paved shoulders when necessary, and by reducing the lane widths in curb and gutter sections. Curb cut ramps, signals, and pedestrian features were upgraded at all intersections. The ponding water and hydroplaning was corrected by correcting the cross slope with overbuild, and cleaning out pipes and swales. DeSoto Blvd originally tied into Alternate US 19 at a 12-degree angle. We were able to realign this roadway within the existing right of way to achieve a 90-degree angle. The challenge came when we tried to “fill in the gaps” in the sidewalk. This is an older beach community where most of the resident and businesses had open driveways along their entire frontage.
How do you get the pedestrians safely across these wide (most were greater than 50 feet) driveways? You don’t! The driveways needed to be modified to bring them into compliance with current access management standards. After reviewing the crash data at these wide driveway locations, it was determined that 15 properties warranted some type of driveway modification. When we started drawing up the modified driveways, it became apparent that a large majority of the properties were actually using the FDOT right of way as their parking lot and without continuing to do so, these properties could not stay in business. FDOT entered into agreements with the properties owners to lease back the FDOT right of way.
The end result not only provided a safe path for pedestrians and bicyclists, it also improved the overall aesthetics of this corridor essentially giving a tired beach community road a face lift.
If maintaining our roadways was simple, we would not have pot holes and there would be virtually no accidents. Unfortunately we are not there yet. On all roads, whether it is resurfacing to extend its pavement life or adding sidewalk for pedestrians, there is always a challenge in the design that makes our jobs as engineers fun and interesting. Now if I could figure out a way to make cleaning her room fun and interesting for my teenager… that would be an accomplishment.