Data for Road Detours

Written by Marco Cecala

Created on Saturday, 22 September 2012 17:54

A 923Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE

As our nation's infrastructure continues to be repaired and upgraded, many opportunities are presenting themselves for the contractor. We see freeways being widened and expanded, bridges being replaced and entire town's streets and utilities being redone at one time.

A common thread that runs through these projects is the need for some type of detour. These are temporary and need to perform for a specified period of time. We have built a lot of detour data files for our clients. While these are varied, we look at them in two separate categories. Let's outline the types and specific requirements for each.

High Speed Detours
When a road is being rebuilt or widened, traffic will need to shift out of the work lanes. This is done by making a lane across a median area and moving all traffic to one side of a divided highway, or a temporary lane in the case of undivided routes.

We have found it advantageous to collaborate with contractors as to the placement of this type of detour. The biggest reason for this is to maximize the permanent work being done. When there is white paving and expensive subgrade, it makes sense to maximize the amount of work that can be done at one time.

In this image, I have shown two prospective detour centerlines. The one to the left being longer, requires more work to be done with permanent paving. There is a ditch along the median, and it is shallower on the left. At the right, the detour is more compact, the curve will meet specifications which will be covered later.

What needs to be considered for this detour is how much permanent work can be done on the front side and what will it take to remove the detour. These detours became a wash after re ran the numbers for the work and cost, here's why; the longer detour to the west required coming back in and doing more paving later. This required string line as well as moving the machine and support equipment back to the location when they were already further along the project. The detour to the east could be formed and poured instead of paved; the detour to the east is starting to head up the slope to the new bridge being built, which is what necessitated the work in the first place. A larger culvert would need to be installed as well as dirt intensive haul roads going to the bridge that were going to be a maintenance problem.

High Speed Detour Tips
• All work must conform to AASHTO Specifications, http://www. transportation.org. The speed rating of the detour will let you know what the alignment, profiles and superelevated curves need to look like. Many software programs will design to a speed rating and not let you exceed safe limits.
• The design may not be set in stone. After visiting the location, taking photos, topo shots and maybe even a review in Google Earth you may want to propose a different alignment. We have found as long as parameters are met, it's usually no problem.
• The time the detour needs to operate may allow you to use a lower strength mix for the asphalt. We have proposed this for several jobs and it has been a real boost to the bottom line.

Slow Speed Detours
Small, county roads with a new bridge or straightening section to increase speed rating was the main motivation for this article. There are more details left to the contractor for small jobs that with major highway work. We still can help find some money with the big roads, but you can make the small jobs more profitable in respect to detours.

The most common type of detour for a small road is for the replacement of a bridge. This requires three separate data files; one for the detour, one for the new bridge and road tie in, and the final surface to remove the detour and restore the area to its original state.

The best way to find out how to restore the detour area is with a good initial topo. Go out and make sure you hit all the grade breaks, go back in the office and add breaklines. Review the surface to make sure it looks right and file it away until ready to use. We have found that the restoration of a detour area to original condition not only makes the agency happy, but the locals feel better when the scar of the detour and subsequent work heals nicely.

Many of the small detours will be left up to you, plans are merely a suggestion. We have seen everything from a line with a proposed alignment to an actual road job with plan, profile and typical sections. As with high speed detours, you can adjust to make things easier and usually get it approved, within reason.

I want to review a detour that ends up somewhere in the middle as far as information goes, this is for a bridge replacement on a county road. It is the only access for about 200 families and down time is not an option. Though the traffic count is not high, the route is critical. Let's look at the components, starting with the horizontal alignment;

The horizontal alignment for this detour is drawn to cross the creek upstream from where the new bridge was going. It ran along a wash that would have required two culverts to be installed. We reviewed the detour and made some suggestions. The contractor was able to get a variance from the agency and the land owner, by moving the detour they were able to use a single culvert.

The vertical profile stated to follow the existing ground. We needed to pay attention to the water in the area as this spot gets a lot of rain and did not want flooding on this only road to a large group of homes. With such a small length of road, the dirt quantities were of no concern, we did however make sure that the detour more or less balanced. In order to make the restoration easier, we were mindful to do as little work as possible in the creek crossing. When it comes time to remove the culvert and dig out the fill, minimizing that yardage will be helpful to the bottom line.

The typical section was standard. It omitted the fact that even at 25mph, the detour would need superelevated curves to help with shedding water and maintain driving safety. With the typical section showing what we see here, all that really helped were the lane width and side slopes. A ditch would also be necessary to make sure the area drained.

Another consideration was the possibility of the temporary culvert washing away during construction. The area has its share of heavy rain and flash flooding is a real possibility. With that in mind, we talked to the contractor and they made a recommendation that they install gabion walls upstream of the culvert to discourage erosion. They added that the gabions would be left and repositioned during the stream restoration to help with erosion in the bend of the creek in that area. The proposal and subsequent improvements made to the site gave the contractor points for being resourceful and helping the job to look better than they found it.

With the initial detour road designed, the last thing to take a look was the areas where the detour went back into the main road. Smaller roads like these are not subject to the high cost of thick concrete paving, but value engineering may help some. A look at the design of the detour centerline shows the road going quite a bit away from the proposed bridge. It joined back into the road with no difficulty, but moving it helped several issues.

The green line is the original centerline, the red the proposed change. To the south, the new road allowed the contractor to finish the access to a land owner's property; the red proposed alignment took the driveway out of the traffic flow. The new alignment goes very close to the proposed bridge. This allowed for a smaller disturbance area and the gabion walls for the temporary culvert were close and could be placed before the new bridge for more flood protection.

The contractor was also able to build the road surface with lower cost asphalt, as the new bridge was modular and would install in a week. A change in this alignment meant a better job and lower cost. These and other details allowed the job to move smoothly and be more profitable for the contractor and fewer headaches for the land owners who passed there every day.

How to propose changes to a detour
Yes, every situation is different, here are some tips that can help you succeed in helping yourself and the owner;
• Make a common sense assessment of the conditions. Look at how the detour is designed, if you feel it can be improved, go to the next step;
• Research specifications and requirements of the governing body. These are usually AASHTO standards with local modifications. The best advice is to know the answer to the question before you ask it. With your ideas supported by specifications, and the fact it will make the project cheaper, faster, better; submit the inquiry.
• You may be asked to prove it; the work you submit should reference applicable standards. Any information not submitted can be covered in the review meeting.
• Never estimate the job with value engineering in mind. If there is an opportunity to submit VE, you can put the basics of an improved detour in the proposal. No need for great detail here.
• Every situation may not need or warrant a change to a detour. We have seen some good benefit from looking closely at this often ignored portion of the job.

Marco Cecala is the owner of Take-off Professionals in Arizona and is a nationallyknown expert and teacher of CAD, automated surveying and machine guidance.

A 923Kb PDF of this article as it appeared in the magazine—complete with images—is available by clicking HERE