Why we say the design vehicle is conceptual? Because it is not real vehicle, it is actually a group of parameters that describe the general characteristics of vehicles within the same category.
Now, let me show you the parameters of a design vehicle that influence roadway design. The first parameter is the height, it influences the vertical clearance. For example, if we design a new bridge cross the road, the height of the bridge should be higher than the design vehicle’s height. The second one is the width: it determines the width of the lane and shoulder. The third one is the length: it’s used to calculate the length of the vehicle storage area, for example, the exclusive left turn lane. And then the configuration: whether the vehicle is single-unit or multiple-units influence its braking distance and turning radius. Is everybody following me so far?
OK. Now think about how many different kinds of vehicles are available in the market. You know we have so many vehicle manufacturers and countless choices of cars. Fortunately, almost all the vehicles can be represented by the four types of design vehicles on the picture: the passenger car, the bus, the truck,