Tag: Roadway

New Changes for Designing Low-Volume Roads

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While staying up-to-date on standards, manuals, guidelines, policies, and specifications can be challenging, the Hoyle, Tanner design teams have welcomed the Second Edition Guidelines for Geometric Design of Low-Volume Roads (Guidelines) recently published by the American Association of State Highway and Transportation Officials (AASHTO). The updated guidelines expand the definition of low-volume which provides greater flexibility to Hoyle, Tanner’s engineers to design the appropriate solution for the challenges our clients face. We’re going to cover some basics of the Guidelines and why it is so welcomed.

In the first edition (2001), low-volume roads were considered to have traffic volumes of 400 vehicles per day (vpd) or less. With the newest release (2019), the Guidelines expand coverage to roads with traffic volumes of 2,000 vpd or less. What does 400 vpd look like? For perspective: If you were to walk down a street, you’d expect to see one vehicle approximately every 3 ½ minutes at 400 vpd. If the same road experienced 2,000 vpd, you’d expect to see one vehicle approximately every 45 seconds.

According to the Guidelines, 80% of the roads in the U.S. are low-volume roads.

To determine if that 80% was applicable to our clients, we reviewed available traffic counts for an “average” New Hampshire town and found a conservative 70% of their road miles met the new definition of low-volume.

The Guidelines still remain focused on very low-volume roads (≤ 400 vpd) but the inclusion of roads with volumes of ≤ 2,000 vpd is greeted with open arms. This provides our design teams an additional resource on more projects; before the latest release we could not use the Guidelines on most of our projects as traffic volumes typically exceeded 400 vpd. However, a majority of past projects had traffic volumes that did not exceed 2,000 vpd.

What’s the benefit to our clients and designers

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The Guidelines apply to both new construction and evaluating existing roadways. Here are a few things designers can consider for the construction of a new low-volume road:

Reduce pavement width allocated to vehicles, narrow the road. The obvious benefit to narrower roads is reduced construction cost. Another benefit is a decrease in environmental impacts. Thinking a little bit further beyond the edge of road, the savings from a narrower road could be invested in pedestrian and bicycle accommodations.

Reduce the design speed, allowing for the use of sharper horizontal curves. This could be used to avoid or minimize impacts to environmentally sensitive areas, an excessive cut, an excessive fill, or negative impacts to abutting properties. Doing any of these could not only reduce construction costs, but also potentially speed up the construction time and reduce the environmental permitting coordination.

Reduce the stopping sight distance, allowing for the use of sharper curves. Similar to reducing the design speed, however, this provides the designer flexibility for both the horizontal and vertical (profile) alignments. This could be used to avoid or minimize impacts to environmentally sensitive areas, an excessive cut, an excessive fill, or negative impacts to abutting properties. Doing any of these could not only reduce construction costs, but also potentially speed up the construction time and reduce the environmental permitting coordination.

Reduce the clear zone, and thus reduce or eliminate guardrail. A little side note, a clear zone is an area that allows a driver to stop safely, or regain control of a vehicle that has left the roadway. Since guardrail is a roadside hazard, costly to install, and costly to maintain when impacted, being able to reduce guardrail or eliminate it reduces construction maintenance costs and potential accidents involving it.

With this increased flexibility the Guidelines provide there is still engineering judgement to be used. For instance, it would be ill-advised to combine a narrow road with sharper curves and reduced stopping sight distance. Remember the intent of the Guideline is to reduce crash frequency and severity while prudently using public funds.

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What about all the existing roads to be maintained?

We have the ability to evaluate how the existing road is performing and if it meets the Guidelines. When something doesn’t meet the Guidelines, that doesn’t mean that it needs to be fixed.

For example, let’s consider a one-mile segment of low-volume rural road in good condition, and we’re looking to resurface it before it becomes worse. We go out to the site, take measurements and notes of existing conditions, and find the following:

  • The average road width is less than the Guideline recommendation.
  • There is a curve that is sharper than the Guidelines minimum radius, has no warning signs, appears multiple vehicles have left the paved surface within the curve but no reported accidents in the last 5 years.
  • There are multiple trees within the clear zone but no signs of impacts or reported accidents.

There are several ways to address each of the issues. Recalling the purpose of the Guidelines is to make improvements at locations where it can be expected to provide substantial crash reduction benefits the design team makes a recommendation. Maintain the existing road width except within the sharp curve, where the pavement is to be widened to the Guideline minimum and the trees within the clear zone are to remain.

Hoyle, Tanner’s transportation design engineers are experts in roadway design, pavement layout, roadway stormwater, and safety for vehicles and pedestrians alike. We research and commit ourselves to learning the newest design guidelines for a safer, healthier community for drivers, roadway designers, and pedestrians. Questions? Call (603) 669-5555 ext. 181 or email me to discuss the latest technology and guidelines in the transportation engineering industry.

Designing Bicycle Box Systems to Keep Cyclists and Motorists Safe

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Everyone knows about bicycles. Like any sport, they have a fandom following, from avid Tour-de-Francers to all those dedicated bike-to-workers. Not to mention, it’s practically a rite of passage to learn how to ride one, and it’s the quintessential comparison when talking about things you never forget how to do once you learn.

Despite their popularity around the world, America still shines with its youthful glow in comparison to many historic countries; we just don’t have the same bicycle-laden streets that other countries have grown to cherish. That’s not to say that America isn’t making strides to enhance its bike-ability. Major cities have hundreds of miles of bike lanes, while New York City tops the list at having 1,000 miles.

Though America has some catching up to do, cities have seen overall betterment in roadway safety when communities define where bicyclists should travel on the roads.

One innovative design that’s gaining traction is the bicycle box. From the NACTO website, “A bike box is a designated area at the head of a traffic lane at a signalized intersection that provides bicyclists with a safe and visible way to get ahead of queuing traffic during the red signal phase.”

Bicycle boxes are innovative because they address many safety concerns at once, such as: increasing visibility of bicyclists, preventing “right-hook” conflicts, provides priority for bicyclists, and groups bicyclists into one obvious area, making it easier for cyclists to clear the area quickly.

Recognizing these benefits, Hoyle, Tanner recently designed a bicycle box system on Farrell Street in South Burlington, Vermont, which will become the first approved installation in the State. As Farrell Street is part of the route of the Champlain Bikeway (a 363-mile scenic loop around the lake), the City is dedicated to improving access and safety in this location and throughout the City. At the Farrell Street/Swift Street intersection, the City was particularly concerned that southbound cyclists looking to make a through or left turn would conflict with vehicles turning right to access US 7 & I-189. A bicycle box was the perfect solution. Hoyle, Tanner worked with the Federal Highway Administration (FHWA) and gained interim approval for the City’s use of this valuable tool, which is required for new traffic control devices that have not yet been formally adopted. Partnering with Howard Stein Hudson, Hoyle, Tanner designed the bicycle boxes which will employ special highly visible green pavement markings and thermal or video bicycle detection to reduce collisions and improve safety at the intersection. With this experience, Hoyle, Tanner will look to aid other municipalities and state agencies with this and other emerging traffic control technologies, with a goal of improving the recreational and commuter transportation experience for all users.

14 Steps for Preserving Steel Structures

Piermont, NH-Bradford, VT Steel Bridge

Preventative maintenance is defined as scheduled work at regular intervals with the goal to preserve the present condition and prevent future deficiencies. On bridge structures, this work is typically performed on structures rated in ‘fair’ or better condition with significant service life remaining. Minor repairs may be necessary to maintain the integrity of the structure and prevent major rehabilitation. Structures that are not maintained are more likely to deteriorate at a faster rate and require costlier treatments sooner than maintained structures; therefore, it is more cost effective to maintain structures to avoid replacement or major rehabilitation needs.

New England’s weather causes extreme conditions for steel bridge trusses, such as flooding, ice and snow. Corrosive de-icing agents are used in the winter, which can accelerate deterioration of exposed bridge elements. Preventative maintenance is critical for steel truss bridges to reach their intended design service life and, therefore, attain the lowest life-cycle cost of the bridge investment. Presented are minimum recommended guidelines for preventative maintenance of steel truss bridges.

Here are 14 actionable maintenance tasks to preserve historic truss bridges:

  1. General: Remove brush and vegetation around structure. Annually.
  2. Bridge Deck & Sidewalks: Sweep clean sand and other debris. Power wash with water to remove salt residue. Annually.
  3. Wearing Surface: Check for excessive cracking and deterioration. Annually. 
  4. Expansion Joint: Power wash with water to remove debris, sand and salt residue. Annually.
  5. Bolted Connections: Inspect for excessive corrosion or cracking of the steel fasteners. Check for any loose or missing bolts. Annually.
  6. Welded Connections: Check for cracking in the welds. Annually.
  7. Truss Members: Power wash with water to remove sand, salt and debris, particularly along the bottom chord. Give specific attention to debris accumulation within partially enclosed locations such as truss panel point connections or tubular members. Annually.
  8. Bridge Seats: Clean around bearings by flushing with water or air blast cleaning. Annually.
  9. NBIS Inspection: Complete inspection of all components of the steel truss bridge. Every 2 years unless on Red List.
  10. Painted Steel: Scrape or wire brush clean, prime and paint isolated areas of rusted steel. Every 2 to 4 years.
  11. Steel Members: Check for rust, other deterioration or distortion around rivets and bolts, and elements that come in contact with the bridge deck which may be susceptible to corrosion from roadway moisture and de-icing agents. Every 3 to 5 years.
  12. Bearings: Remove debris that may cause the bearings to lock and become incapable of movement. Check anchor bolts for damage and determine if they are secure. Every 3 to 5 years.
  13. Exposed Concrete Surfaces: Apply silane/siloxane sealers after cleaning and drying concrete surfaces. Every 4 years.
  14. Bridge & Approach Rail: Inspect for damage, loose or missing bolts, sharp edges or protrusions. Every 5 years.

Actions to Avoid

  • Do not bolt or weld to the structural steel members.
  • Do not remove any portion of the structure.
  • CAUTION! Paint may contain lead.

Additional resources can be found through the New Hampshire Division of Historical Resources website.

Pi vs. Chocolate Cream

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Pi… I did not forget the “e”, I am referring to the mathematical constant, π, for the value 3.141592…, a ratio of the circumference of a circle to its diameter. For some it was junior high and others it was high school, but almost everyone is taught the concept of Pi in geometry class in America. The staggering question asked by so many students over the years is “how do we use this in ‘real’ life?” Well we have answered that question for all of you as it relates to engineering:

When designing bridges many of the structures utilize reinforced concrete to provide the strength necessary to support its daily use by vehicles. For many of our bridge projects, the circle is most often representing the area of reinforcing steel used in the reinforced concrete beam.  We determine the total amount of the (steel) reinforcing to determine the capacity of a structural member such as a beam, deck or slab.

In associated roadway design, Pi is used in a slightly different manner, to calculate curvature. A maximum curvature (minimum radius) is used to ensure adequate sight distance at differing speed limits. This promotes safe vehicular travel by providing a level of comfort and expectation to the driver.

Another application for the mathematical constant is in airfield markings. Their purpose is simple – to safely guide pilots during aircraft take-offs and landings, and while taxiing around the airfield. To create these markings, Pi is utilized when calculating the amount of airfield paint required for runway designation markers, taxiway centerlines and edge lines.

Pi is also used extensively in the calculation of areas of gravity sewers, wastewater force mains, water main pipes, storm drains, drainage culverts and other types of utility pipes. These calculations are used to establish the area of the pipe for the purpose of determining flow velocities and flow volumes as well as other types of hydraulics calculations.

Now that we have proved your mathematics teacher correct, and that someday you may need to know the value of Pi, the obvious question remaining is “what does pi and pie have in common?” My answer is Pi is focused on circles, radius and diameters… and so does pie! If you want a great Chocolate Cream Pie recipe check this out!