String music

May 17, 2002

Design, or the documentation of an evolving concept, is without fail at the mercy of changing times, trends and technology. Over the past few decades, the techniques of design have been scrutinized, standardized and computerized by groups of people who want to epitomize the process into a neat package that serves the needs of many industries. And yet, there is always an exception to the rule.

Design, or the documentation of an evolving concept, is without fail at the mercy of changing times, trends and technology. Over the past few decades, the techniques of design have been scrutinized, standardized and computerized by groups of people who want to epitomize the process into a neat package that serves the needs of many industries. And yet, there is always an exception to the rule.

Wrapping roadway design into a nice little manageable parcel would be the ideal target for any civil engineer. However, transportation design is a hound of a different breed. Forces buffet around a roadway project like bugs circling a porch light on a summer’s eve. From environment issues to traffic flow to fluctuating state budgets and funding, there are factors both visible and unforeseen that can prolong a transportation project from a few years to a decade. In a nutshell, sometimes the tail wags the dog. 

Then you stir evolving technology into the mixture.

Over prolonged periods of time there becomes a disparity between the lifecycle of a software program and the design data derived from those systems. Think about all of the old versions of text files, accounting formats and backups you may have on your home computer. The data compatibility issue is even more pronounced when using versions of computer-aided design (CAD) systems that have been updated every year or two. The data dilemma continues to grow as new automation innovations and the advent of 3-D CAD software tools have been introduced to raise levels of precision, visualization and productivity. In the case of transportation design projects where duration is a question mark, the function of preserving, refining and expanding roadway design has been forced to adapt to the inevitable changes in technology. But the discipline also reaps big benefits along the way.

Setting the scene

A prime example of an evolving roadway project takes place in the northwest corner of New Hampshire. Almost 9 miles of road stretch along U.S. Route 302 and snakes through three small towns . . . from Bath to Landaff to Lisbon. At first glance, Route 302 is really Main Street U.S.A. for these rural burgs, and the miles between are beautifully rustic. The whole region shoulders the mountainous topography of the White Mountain National Forest.

The original thoroughfare was constructed in the 1930s along a course that follows the small settlements along the Ammonusuc River. Today, those towns are hampered by logging trucks, 16-wheelers and tourist buses visiting the local museum and taking in the local color. The area has several historical properties and structures that take a beating from the vibration of the truck traffic, not to mention the exhaust and other hazards delivered by in-town traffic. In particular, the town of Bath has a number of historic homes with unique architecture. The town also contains six properties listed on the National Register, including three covered bridges.

2-D is too old

In 1992, the New Hampshire DOT (NH DOT) publicized an RFP (Request for Proposal) for the development of preliminary designs, aerial mapping and corresponding services to get the effort under way. The project began with aerial mapping, topological maps and careful onsite analysis of the local vicinities. Initially, civil engineers would assess the needs of the local communities and drivers, with major considerations being traffic delays, safety and curtailed access to businesses, which hurts the local economy. Soon a number of natural and cultural resources, including cemeteries, landmarks, older bridges and wetlands, would be added to the list of concerns. Each issue would be weighed as concepts were transformed into workable preliminary designs with the least impact on local business and traffic flow.

Louis P. Caron, P.E., a veteran civil engineer at SEA Consultants, Concord, N.H., has supervised the project from the very beginning. “The original design alternatives and alignments were created in a much older version of AutoCAD, a CAD system we were using at the time. The designs were created with a template method  (2-D cross-sectional views), a standard way of representing roadway elements at the time.”

Preliminary design alternatives were completed in the following two years. The main component of the proposed new route would cut a beeline on the outskirts of Bath and Landaff to adjoin two sections of existing roads. This plan would provide the least amount of imposition on the townspeople and would preserve the integrity of the downtown areas. The new artery would travel through mountainous terrain and involve large cuts and fills requiring extensive temporary erosion control measures. New intersections and bridges also would be factored into the plan. In summary, the undertaking would be a sizeable challenge for any civil engineering team and push the envelope on the CAD software tools.

The evolution of the Route 302 plan proceeded to 1998. The results of the environmental and engineering studies were reported in an environmental assessment (EA). While in the draft form, the EA was reviewed by local residents, state and federal authorities. Based on their feedback, the EA was revised and distributed as a final environmental assessment. The document provided the history of the project development and is the base document and resource that defines the finished roadway project.

Primed and ready

In 1999, the New Hampshire DOT posted an RFP for the final design and preparation of construction plans for the reconstruction of 5.5 miles of Route 302 in the towns of Bath and Landaff. The work would entail improvements to the engineering designs, the widening of an existing bridge, construction of three new structures, right-of-way impact plans, stormwater management, wetland impact plans, Army Corps Wetland Permit exhibits and wetland mitigation site plans. The project construction costs were estimated to exceed $30 million and involved 2 million cubic meters of earthwork.

SEA Consultants was chosen as the prime consultant and the head of a multi-disciplinary team. The firm excels in infrastructure projects with diverse engineering tasks and offers expertise in transportation engineering, bridge and structural design, water resources, trenchless technologies, civil engineering, environmental services, architectural planning and building engineering.

The project would commence with another round of aerial mapping, but photographed at a much lower altitude. SEA would conduct supplemental field surveys and site wetland delineation and mapping. The SEA team also would prepare base plans and traffic control plans and detours, as Route 302 would have to stay open during all the construction phases.

Tying in strings

In 1999, the New Hampshire DOT modified their CAD guidelines and SEA standardized on MXROAD and MXRENEW (Infrasoft Corp., Beverly, Mass.) design software and Microstation (Bentley Systems, Exton, Pa.). Thus the original design data created in ’92-’93 would need to be imported into the new CAD systems. The MXROAD software would deliver a whole new approach to transportation design with 3-D strings technology. This system is in stark contrast to template systems based on antiquated 2-D methods duplicating manual drafting techniques. Road designs based on 3-D models are precise representations of their real-world counterparts.

“With MX software, we have no data translation problems with the NH DOT, not to mention that we meet our customer’s needs,” stated Caron. “The software is great for generating many preliminary alternative designs. It also enables us to rapidly transfer ideas onto paper and into deliverables for project reviews. For this phase of the Route 302 project, we had to take the alignments developed years before in AutoCAD and convert the coordinate system from English to metric to meet the new specifications from the NH DOT. We imported the 2-D alignment work and started with a brand new line model in MXROAD.

“Initially, we had to compare the alignment and topography developed in 1992 with a very accurate survey and low-level flight maps developed in 1999. A team went out and ground surveyed the obscured cross-country areas. We found some significant differences and had to look at alternatives because of the terrain changes. Would the alignment look different now with a new ground line? In some cases it did, and in some cases it did not,” concluded Caron.

Due to the imposing slopes surrounding the new road, truck climb lanes consisting of a 12-ft lane and 4-ft shoulder were proposed for the area. Instead, the NH DOT decided to go with a 12-ft shoulder and reduce the environmental impact and associated costs. These roadway design elements also had to be remodeled. Adjustments to an adjoining intersection also appeared on the to-do list.

In the real world

Migrating from 2-D to 3-D CAD systems was a formidable task for SEA civil engineer and CAD specialist Cecil Luckern, but the effort would pay off in a dramatic way. Using input files in MX, a user can capture and archive 3-D design data, coordinates and command lines into associated files and use them at a later date for modifications.

“You can modify intersections through input files,” said Luckern. “Designing complex intersections has always been problematic using a template-based system and very labor intensive. It would take me 9- to 10-times longer to make a change in a template-based system, as opposed to a strings-based system, for a simple intersection. This is where the real power of the 3-D software lies. There is a huge time savings when you try to automate the labor that goes into 2-D cross sections, not to mention it is not a precise replication. 3-D strings models are mathematically correct replications of the real world. Thus, the task of producing elevation drawings describing the grades along the mountain areas also is more accurate and expeditious.

“Troubleshooting is easier with 3-D strings technology. For example, in a superelevation condition, if you elevate the high side there are points critical for drainage. The software program can plot the break in the shoulder so the engineer can immediately see if the superelevation is right,” resolved Luckern.

Luckern’s main challenges were to hit the grades, put in temporary road designs and develop drainage systems in areas of steep grades. “I can also change horizontal or vertical alignments or offsets using input files. When I start a design, I use MX for the design and alignment phase. I capture those commands into input files. If I need to flatten a curve on a design, I can simply change the input file and rerun the design. That’s the beauty of the software.

“In template systems, the road width stays the same for one template so if I want to widen the road I need a different template for each width. You are very limited with templates and quickly run into problems with intersections. Today, if I want to widen the road I do it easily with strings. I can use a style set to put, for example, a guard rail into the model. Once that is done, if I widen the road the guard rail is automatically part of that widening,” said Luckern.

As a part of the Route 302 project, SEA needed to compute quantities and estimate probable construction cost.

“For this task, SEA uses MX to great advantage,” cited Luckern. “Using input files, SEA can select materials, such as gravel or stone, and automatically estimate the amount of materials required for any part of the job. That’s just another way we enjoy time savings.”

Three-dimensional models also have improved collaboration and communication for the civil design team.

“We use 3-D model visualization in-house to see what the impact of a design change will be,” stated Caron. “For myself, because I have been in the industry for many years, I can add that third dimension in my mind. However, you are always looking at two dimensions. You are either looking at a profile (Y and Z coordinates), or the plan view showing X and Y coordinates. With a 3-D design system, you can now easily see all three dimensions together and look at the design from different angles and perform drive-throughs.”

Stay tuned

The final design of the Route 302 Bath-Landaff project is currently on hold awaiting further subsurface soils analysis. A roadway segment in Landaff was completed in 2001 and is ready to plug into the new road system. SEA will prepare contract plans and specifications for four separate construction projects within the 5.5-mile zone.

As the last modifications were added to the CAD designs, it looked as if the project would be on its way. However, a new dilemma presented itself to the transportation design project. An environmental team was sent in to test the soil in the elevated areas. The geotechnical reports revealed the soil was weak in areas requiring substantial grade changes. Thus a new round of design changes are likely to facilitate this additional contingency. Cut sections with substantial grading up to hundreds of feet into the mountainside may need to be reworked.

SEA projects construction on this project will likely begin in 2004 . . . unless, of course, the tail wags the dog.

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