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Episode 39 – Trucks
Topics: Trucks
Websites and Citations:
Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com
Hello and welcome to another edition of Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talking traffic dot org. Today is Monday, June 27, 2011. This is episode 39 of Talking traffic.
Today’s topic is about trucks. All kinds of trucks. But before I dive into the nebulous term that is “trucks” let me throw some engineer-speak at you.
When we are designing or analyzing roads, we talk about the “Design Vehicle”. The design vehicle is the largest type of vehicle that is most likely to use that road. For example, if I’m working on a residential subdivision, I dont’ need to design the road to allow a tractor-trailer to turn around in a cul-de-sac. No, a typical large vehilce for a subdivision would be a UPS or FedEx truck. Now, the occasional tractor trailer might come into that roadway, maybe a moving truck, but it only happens occasionally, and the inconvenience caused by having to back up a tractor-trailer to turn it around is small compared to the inconvenience of designing the subdivision to allow the truck to drive around as if it were an interstate.
It’s important to determine at teh very beginning what your design vehicle is because it will affect many different things in your roadway project.
Now, let’s talk about trucks. When I, as a traffic engineer say “truck”, I mean some specific types of vehicles. I’m not talking about pickups or SUVs or dooleys or anything that you migt see in a Ford commercial. I’m talking about larger vehicles that are intended to carry freight. These trucks break down into two cateogries. Single Unit trucks, and Multi Unit trucks.
Single Unit trucks are trucks that don’t articulate, that have a single frame to which the wheels are attached. UPS and FedEx trucks are good examples of these. dump trucks and garbage trucks and smaller moving trucks are all examples of the single unit truck.
Multi-unit trucks include the typical tractor-trailer combination that you see everywhere. These come in various sizes measured from the center of the front axle to the center of the rear most axle. So, when I’m throwing engineering speak at people. I would refer to the WB-62 design vehicle, which means a multi-unit tractor-trailer combination that has a 62 foot wheel base. This truck is actually about 69 feet from nose to tail. There are also the WB-40 and the WB-50 and the WB-65. For trivia purposes, the WB-65, which is 74 feet from nose to tail, is the vehicle used when designing interstaets and interstate ramp terminals.
The importance of the design vehicle becomes clear when you start putting together the design of intersections and sharp curves. Larger trucks need more room in order to make turns. The rear wheels of a truck–well, of any vehicle, really–will run to the inside of the front wheels. This wider path made during a turn is called overtracking, and its why you see large trucks swing out really wide when they’re making right angle turns at intersections. The distance and width needed to ensure that the rear wheels of the design vehicle stay off the edge of pavement, or out of the adjacent lanes, can add a lot of cost to a design project.
Next time you’re walking in an area that has curbs and you come to an intersection, look at the corners. Do you see tire tracks up against the curb faces? Do you see tire tracks on top of the curb, or on the sidewalk? Are the corners, maybe including the pedestrian ramps, broken and cracked? If any of these are true, it means most likely that truck drivers are running their rear wheels up and over the curbs when they’re trying to make turns. This could be becuase the driver isn’t very good, but more likely it’s because there’s not enough room for the trucks to clear when taki[...]
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By Topics: Trucks
Websites and Citations:
Theme Music: Five Star Fall, Mercurial Girl, Magnatune.com
Hello and welcome to another edition of Talking Traffic. My name is Bill Ruhsam and I host this podcast and its sister website, talking traffic dot org. Today is Monday, June 27, 2011. This is episode 39 of Talking traffic.
Today’s topic is about trucks. All kinds of trucks. But before I dive into the nebulous term that is “trucks” let me throw some engineer-speak at you.
When we are designing or analyzing roads, we talk about the “Design Vehicle”. The design vehicle is the largest type of vehicle that is most likely to use that road. For example, if I’m working on a residential subdivision, I dont’ need to design the road to allow a tractor-trailer to turn around in a cul-de-sac. No, a typical large vehilce for a subdivision would be a UPS or FedEx truck. Now, the occasional tractor trailer might come into that roadway, maybe a moving truck, but it only happens occasionally, and the inconvenience caused by having to back up a tractor-trailer to turn it around is small compared to the inconvenience of designing the subdivision to allow the truck to drive around as if it were an interstate.
It’s important to determine at teh very beginning what your design vehicle is because it will affect many different things in your roadway project.
Now, let’s talk about trucks. When I, as a traffic engineer say “truck”, I mean some specific types of vehicles. I’m not talking about pickups or SUVs or dooleys or anything that you migt see in a Ford commercial. I’m talking about larger vehicles that are intended to carry freight. These trucks break down into two cateogries. Single Unit trucks, and Multi Unit trucks.
Single Unit trucks are trucks that don’t articulate, that have a single frame to which the wheels are attached. UPS and FedEx trucks are good examples of these. dump trucks and garbage trucks and smaller moving trucks are all examples of the single unit truck.
Multi-unit trucks include the typical tractor-trailer combination that you see everywhere. These come in various sizes measured from the center of the front axle to the center of the rear most axle. So, when I’m throwing engineering speak at people. I would refer to the WB-62 design vehicle, which means a multi-unit tractor-trailer combination that has a 62 foot wheel base. This truck is actually about 69 feet from nose to tail. There are also the WB-40 and the WB-50 and the WB-65. For trivia purposes, the WB-65, which is 74 feet from nose to tail, is the vehicle used when designing interstaets and interstate ramp terminals.
The importance of the design vehicle becomes clear when you start putting together the design of intersections and sharp curves. Larger trucks need more room in order to make turns. The rear wheels of a truck–well, of any vehicle, really–will run to the inside of the front wheels. This wider path made during a turn is called overtracking, and its why you see large trucks swing out really wide when they’re making right angle turns at intersections. The distance and width needed to ensure that the rear wheels of the design vehicle stay off the edge of pavement, or out of the adjacent lanes, can add a lot of cost to a design project.
Next time you’re walking in an area that has curbs and you come to an intersection, look at the corners. Do you see tire tracks up against the curb faces? Do you see tire tracks on top of the curb, or on the sidewalk? Are the corners, maybe including the pedestrian ramps, broken and cracked? If any of these are true, it means most likely that truck drivers are running their rear wheels up and over the curbs when they’re trying to make turns. This could be becuase the driver isn’t very good, but more likely it’s because there’s not enough room for the trucks to clear when taki[...]