Though I haven’t written much in the past year, I’ve been logging away thoughts (engineering, and otherwise). One in particular kept resonating with me last summer when looking over some road designs: how can you design a road for all vehicles without having driven them?
Designers rarely refer to books alone, but utilize experiences that back up the numbers. You’d be hard pressed to find a transportation engineer in the United States that has never driven a car; it’s the most prominent personal transportation method here. But you might more easily find transportation engineers that have never driven a motorcycle. Or an FHWA Class 8, four-axled truck and trailer. Yet we design roads daily, sometimes with the use of simulations, sometimes with nothing more than a reference guide and our engineering judgement. But there’s a disconnect there. Last October, I aimed to remedy one part of this problem and have some fun doing it: learn how to ride a motorcycle.
The MSF Course
I highly recommend the MSF Beginner Rider Course. In three days they have you prepped to pass the DMV rider test, without having ever ridden a motorcycle. Kim and I took the course together for fun and we had a blast. Click here to find a course near you.
Lets look at a standard road curve. While many characteristics of road design have remained for years, roadway curves changed drastically with the invention of the automobile. Super-elevated roads, for example, were inspired by cant railways, where the two rails are designed at different elevations to accommodate a “banked turn”. As a road designer, it’s easy to check the Green Book to find super-elevation guidelines, but they mean so much more with a bit of experience behind the wheel; anyone who has driven a vehicle faster than 30 miles an hour can recognize the importance of a banked turn. Superelevation can be even more important to motorcycle riders. Leaning on a motorcycle is a fantastic way to appreciate how banked turns work to your advantage and the turns reinforce the importance of getting your spirals, runoff, and runout lengths correct.
Road designers also immediately appreciate other successes and deficiencies of road design while riding a motorcycle. Adequate drainage for sheet flow during a storm, stopping and decision sight distances, pavement cross slopes, the condition of the pavement, and locations of road debris accumulation all become much more apparent. The affect of ANY road condition that could develop into a traffic safety hazard magnifies a hundred-fold, as do the consequences of a collision. Experiencing these road conditions on two wheels can be both humbling and horrifying.
For those more interested in the physics side there is a whole subject on the mechanics of bicycle and motorcycles which explains leaning and counter-steering at high speeds. These, along with the center of gravity of the bike, can be used to calculate the maximum degree of lean possible.
Credit is rarely placed on the experiences many take for granted, so designers and engineers should always be looking for new experiences that share insight into their designs. I highly recommend the experience I’ve had, and I’ll be looking into a class on semis in the future. Perhaps a bit of time behind the wheel of a semi will lead to a better understanding of maneuverability on roads designed without trucks in mind. I encourage other road designers to do the same.
Challenge: Put together a preliminary design layout of a roundabout for the intersection of one-way streets being converted to two-way streets. Keep all lanes at 12′ widths, avoid right-of-way conflicts by keeping the design within the current curb-and-gutter boundaries.
Done before lunch. Who at your firm takes these challenges with this kind of excitement? Click through for full resolution graphics.
I was a huge fan of the roundabout installation on Hillsborough St. near the NC State Bell Tower. It was well thought out, it reduced delay, and it was a pleasure to drive in. For a traffic engineer.
Unfortunately, everyone else had a collision in it. A little over a year ago, I personally wrote my recommendations here on my blog when numerous collisions were reported. I still stand by many of my points, especially the point on safety. No amount of fender-benders equal a fatality in my eyes, so I still say the intersection is safer than a four-way signalized intersection.
City and State engineers have done all they could to improve the design. Signage, pavement markings, flyers, flags, you name it. But downtown Raleigh drivers simply can’t afford the time to drive carefully in an unfamiliar design. With roundabouts being such an uncommon occurrence in North Carolina, I cede and will say that a two-lane roundabout of this size is too unfamiliar for uneducated drivers.
What changed my mind? I recently had lunch with Reza Jafari, President at Road Safety and Transportation Solutions, Inc. We talked at great length about driver education and the roundabout. He convinced me that the diameter is just too small for unfamiliar drivers, drivers that have never driven multi-lane roundabouts and are prone to change lanes (or disregard lane markings entirely) while navigating one. The point is fair.
We shall see how well a one-lane roundabout manages the traffic. Anything is better than a signal.
Reza Jafari is the President of Road Safety and Transportation Solutions, Inc. located in Cary, NC. He is a terrific resource on traffic safety and I would go to great lengths to recommend him and his company for a safety study.
So it seems there were a few damages from the Virginia earthquake earlier this week. The biggest damages on the news? The National Cathedral and the Washington Monument. The Washington Monument suffered some cracking at the very top and has since been closed indefinitely to the public until damages can be assessed. As for the National Cathedral, gargoyles, spires, buttresses, and walls cracked, shifted, or fell and shattered. Other homes and businesses near the epicenter were damaged as well.
While damages under 6.0 earthquakes are rare, they do indeed occur, especially in a region less known and under-designed for quakes. In fact, the area falls in a zone of very small seismic risk (see the 2012 International Building Code Map, courtesy of USGS), which is a big part of the problem. Another part of the problem is the age of these structures. Newer buildings and building methods are much safer than they used to be in this regard, but many older buildings will suffer problems, especially since there is little desire to improve them and little funding to do so.
Figure 1: Building Motion During an Earthquake (1). Click to Enlarge
What causes these damages? The lateral forces caused by the accelerating displacement of the ground. When an earthquake occurs, the acceleration of the ground will cause the building to move sideways at the base of the building. It is, after all, firmly attached to the ground in most cases, causing a lateral load and an equivalent shear force at the base (see Figure 1). The building will then begin to swing to and fro, according to the change in direction of the ground.
Familiar with Newton’s law of force? You could very simplistically apply it here to calculate the forces on the building: F = M(A), or force equals the mass multiplied by the acceleration. What may not be immediately obvious is that the higher the mass of the building, the higher the force on the building. But we CAN control the acceleration, which gives us an advantage if we play our cards right. The acceleration can be affected by the natural period of the building, or a complete oscillation, which is dependent on the building stiffness.
Supposing we could create a building that was perfectly stiff, it would match the acceleration of the ground perfectly and it would not oscillate and not experience force. This, unfortunately, is an impossibility for any material, and the slightest deformation would cause large forces due to short natural periods. So contrary to instinct, we do not want to make the stiffest buildings possible, what we want are flexible, long natural periods in our buildings. We need them to sway.
Steel buildings have certainly come a long way, but a large part of the problem with older buildings is their dependence on stone, under-reinforced concrete, unreinforced masonry, and designs incapable of holding even the most moderate earthquake and wind loads. Many of these buildings were built at the turn of the 20th century and are still being used today.
Stone and concrete hold well under compression, but not under tension. Without an element of tension, these older stone buildings simply crumble. Newer concrete structures today are reinforced with steel, doing wonders for flexibility. When allowed to, the steel in reinforced concrete catches tension loads and transfers them. Steel is ductile, and the greater the ductility of a building, the better forces can be absorbed. When designed correctly, even after structural failure, warning signs in reinforced concrete structures are easily apparent, often allowing people to clear from the site before catastrophic failure. After all, people are more important than the buildings.
Figure 2: Deformation Components of a Reinforced Concrete Column (2). Click to Enlarge
While working on a graduate research project during my time at the Constructed Facilities Lab at NC State, I worked on a thesis by Pablo Robalino (2). We tested lightweight concrete columns for seismic lateral forces to see flexural and shear deformation. Notice in Figure 2 how the flexural damage occurs on the side of the lateral force, while the shear damage occurs throughout the column towards the ground. The combination of these effects must be considered when designing columns for the lateral loads associated with earthquakes.
Figure 3: Column Specimen From Seismic Test
Figure 3 is a chunk of a column we tested. Notice the lines drawn with permanent marker. These lines follow cracks in the concrete caused by forces on the column. As we tracked their progression, they naturally followed similar trajectories as those depicted in Figure 2.
These aren’t difficult concepts to understand, but even with the best methods of absorbing forces, costs often limit the investment we can place in a structure to prepare for the worst. While we can’t feasibly prepare for earthquakes of every magnitude, we can use physics, properties of materials, and our growing understanding of these natural disasters to build structures capable of sustaining many of the forces that seem beyond our control.
Hot on the heals of budget deals, deficit raising, and spending cuts in Washington comes a report from the American Society of Civil Engineers saying that our failing infrastructure will impact the US Gross Domestic Product by 2.7 trillion dollars by 2040. All due to funding gaps between what we use and what we actually pay to maintain. This will cause 400,000 lost jobs, lower incomes, lower spending, and lower exports, worsening the US trade position. Transportation is quite possibly the MOST important infrastructure to a first world economy, it would be a shame to have made decades of investment to watch it crumble. Care about your transportation systems? Vote accordingly and write your congressmen, both local and national.
Left turns are terrible. When they aren’t extremely hazardous for drivers, they cause significant delays for other movements in the intersection because of dedicated left turn phases. Engineers have been plagued with this problem for years and have come up with many solutions, but usually the public doesn’t want anything to do with them. Even when they work exceptionally well, the Jughandle, the Michigan Left, and the all-powerful SPUI (single point urban interchange) all took time to introduce to the public. Even the roundabout is feared in areas where drivers don’t use them often, and the super-street causes uproar over driveway access to businesses. A personal favorite of mine, one I studied extensively in an unconventional intersection design course, is the Diverging Diamond Interchange. I designed a hypothetical DDI for Raleigh back in undergrad. It’s neat, but it’s been a hard press on the public to try something as different as driving on the wrong side of the road.
But out of left field comes a fantastic article from Slate, and it made the rounds on the internet this week from departments of transportation and other users on twitter, to an article in Infrastructurist. I was very excited to see something so fantastic shown in promising light because good publicity could be exactly what this idea needs to see more widespread adoption. The intersection does many things well. First and foremost, it removes left turns by placing left-turning vehicles on the opposite side of the road (on or under an overpass) before their turn, allowing them to make free-flowing turns. But it also removes a whole phase from two signals, reducing delay time and easing congestion for through vehicles, while reducing conflict points and making a safer and more efficient journey through the intersection.
Will these see wide spread adoption? Will it replace the traditional intersections we see today? It may replace a few diamonds, but not many cloverleafs; its power is best used on roads of different functional classes. If it can prove it’s worth in the ring of battle, it may see a limited adoption at problem locations. By and large, innovations such as the DDI help alleviate traffic in cat-and-mouse games of congestion, but as we continue to build suburb after suburb without rethinking sprawl, land use, and public transportation, count on seeing and learning to use even wackier intersections in the future. If you want to reduce travel time and congestion, anyway.
A new transportation bill is going to decide how the United States spends money on transportation for the next six years. Unfortunately, those to whom this legislation has the most impact have the smallest voice. According to the Leadership Conference on Civil and Human Rights report “Where We Need to Go: A Civil Rights Roadmap for Transportation Equity“, most funds only cover highways and very little public transportation. Millions of poor and working-class people are cut off from being able to go anywhere because the average cost of owning a car is around $9,500 a year and the current poverty level is at $22,350. I’ve long been a proponent of public transportation for it’s efficiency but it’ll never work as well in the United States as it does in countries in Europe due to our population density. This does NOT mean we don’t need it. We sprawled ourselves out much too far and built too many roads out to suburbs, roads that require upkeep and gas taxes to maintain. Now we pay the price for making the wrong investments without seeing the true cost of a highway system that squeezes every dollar out of American transportation funding.
Public transportation is very important in urban areas, and without it, many can not get to the job they need to live the American dream. It seems that the millions of Americans who have always had access to a personal vehicle don’t understand the lives of people who don’t, and don’t want to pay for them to have an opportunity to work and contribute to society. As a country we need to rethink our transportation policies, so that highway drivers understand the real cost of an American transportation system, and mass transit is finally given the funding it needs to become useful to Americans in highly populated areas.
Someone shared this video with me recently and I wanted to post it. It’s a video showing numerous contained demolition experiments for graduate student projects at the NC State Constructed Facilities Laboratory. I worked in this lab in the summer of 2006 on many graduate theses, and at least one of these experiments I recognized from actually standing nearby when the beam exploded. Others I recognize from projects I worked on, but I may not have been present for, such as the experiment on adding FRP (fiber reinforced polymer) strips to steel beams to increase their strength.
Two weeks ago, an unfortunate collision occurred at a railroad grade crossing in Maine. Reuters reports that a dump truck was hit by an Amtrak train and the driver was fatally wounded. Four passengers aboard the train were injured as well. Terrible. At-grade railroad crossings are some of the most dangerous intersections we have on our road system and they should be avoided whenever possible. Fortunately, many public agencies are fully aware of hazards associated with them and are taking steps to fix them. Here is a list of policies in the United States associated with at-grade crossings, published by the Federal Highway Administration. If you live in North Carolina, rest assured that NCDOT can and will use its power to remove, abandon, close, or regulate all railroad grade crossings. That is, if politicians don’t try to stop the sensibilities of the engineers there.
You might also be interested to know that railroad companies are also very aware of these hazards. CSX, for example, is “firmly opposed” to at-grade crossings and supports policies in place by the USDOT and state agencies to limit their use. You can read more about their leadership in this area on their website.
It’s a shame to see collisions on train tracks. Look both ways when you have to cross tracks and don’t, under any circumstances, try to “beat” the train or drive around protective barriers. It’s not worth it.
I was reading this News & Observer article today about the new roundabout on Hillsborough St in Raleigh, NC. Raleigh Police have cataloged more than 40 collisions at a new roundabout installation at it seems at least a few people have some ruffled feathers.
At first this number seems high, but it’s important to remember a few key thoughts about the safety, design and installation of new traffic patterns:
New patterns can cause collisions
It’s a fact, and one that is difficult to adjust for. New traffic patterns will confuse motorists and can cause collisions. It’s to be expected. While forty seems like a rather high number, high rates during a learning period are why safety engineers do not normally begin their investigation for at least 12 months after a new traffic pattern.
Reduction in conflict points
Roundabouts drastically reduce the conflict points at an intersection. While less conflict points do not necessarily reduce collisions, there are less places vehicles can collide, one of the large advantages of roundabouts.
Reduction in conflict speed
Roundabouts also reduce the speed of incoming traffic. When drivers approach a roundabout, they approach a yield as well as a significant turning radius to enter the circle. This reduction in speed reduces the severity of collisions in the roundabout. The magic of the roundabout is that all of this is done while still reducing delays and increasing the flow of traffic!
Collision severity tradeoffs
When evaulating safety, the number of collisions is not the only metric analysts are concerned about; severity is a metric which should be considered at great length. Without looking at detailed traffic collision reports for the area, it is impossible to determine the safety of the previous intersection. However, it should be noted that roundabouts do not normally have head-on collisions. Because of this, almost all collisions at roundabouts will be of a much lower severity than at a standard 4-way signalized intersection. In fact, only one of the over 40 reported collisions had a severe injury and it involved a motorcycle.
Of course, you should be comparing to injuries and fatalities with the previous design. But how many fender benders are equivalent to severe injuries? Or fatalities? It’s difficult to draw a line here. The following is known by many as “The Old Kentucky Formula”, an easy to use equation for an Equivalent Property Damage Only index (EPDO) based on the data provided by a field officer on the scene of a reported collision:
EPDO = 9.5 (F + A) + 3.5 (B + C) + PDO
F = Fatality: Collisions resulting in one or more.
A = Ambulence: Injury severe enough for an ambulence to be called to the scene.
B = Bruise: A visible, but non-emergecny injury
C = Complaint: Officer cannot visably see the reported injury.
PDO = Property Damage Only: No persons report an injury on scene.
A city safety analyst seems to be keeping tabs and will conduct an investigation after the roundabout has been in use for a full year. I think they should throw out, at the very least, the first six months of data plus the months of construction and signage installation time. The study may very well show areas that can be improved such as driver education, signage, pavement markings, lighting, etc. But judging from my own paths through the intersection and the severity of reported collisions mentioned in the article, there is no doubt in my mind that the roundabout was the correct treatment for the intersection, and while a few comments on the article from readers show a few disgruntled folks, many more applaud it for it’s efficiency. Give it some time and the frequency of the fender benders will reduce.
Mike Roselli is a graduate of the NC State University Civil Engineering Department. He works for the North Carolina Department of Transportation. The views expressed in this post reflect the judgement of the author and do not necessarily reflect the views, opinions, or judgement of NC State or NCDOT.
Mike Roselli is a Civil Engineer and consultant, licensed in the States of NC, SC, GA, and FL, and is focused on providing land development services to clients building in the Triangle Area. He currently resides in Cary, NC.