Chapter 3 - Design Controls

3.2. Design Vehicles

The Federal Highway Administration (FHWA) Manual on Uniform Traffic Control Devices (MUTCD) defines a design vehicle as “the longest vehicle permitted by statute of the road” (2003). The type of design vehicle, with representative weight, dimensions, and operating characteristics is thus used to establish highway design controls.

3.2.1. Design Vehicle Types

The four general classes of design vehicles as defined by AASHTO are:

• Passenger Cars - Passenger automobiles of all sizes, including cars, sport/utility vehicles, minivans, vans, and pick-up trucks
  
• Buses - Intercity (motor coaches), city transit, school, and articulated buses
  
• Trucks - Single-unit trucks, truck tractor-semi-trailer combinations, and truck tractors with semi-trailers in combination with full trailers
  
• Recreational Vehicles - Motor homes (including those with boat trailers and pulling an automobile), automobiles pulling a camper trailer or a boat trailer

Refer to the current AASHTO Green Book, Chapter 2. Design Controls and Criteria, for further discussion on use of design vehicles and for detailed dimensions of design vehicles.

Table 3.1. may be used as a general guide for selecting the appropriate design vehicle. Design vehicle dimensions are defined in the AASHTO (2004) Green Book, Exhibit 2-1. Design Vehicle Dimensions.

Table 3.1 Design Vehicle Criteria
Highway Type	Design Vehicle	Design Speed (mph)
Rural
Interstate / Freeway	WB-50 / WB-65*	70
Ramp
Free-Flow	WB-50 / WB-65*	35 (minimum)**
Entrance / Exit	WB-50 / WB-65*	35 (minimum)**
Loop	WB-50 / WB-65*	35 (minimum)**
Primary Arterial	WB-50 or WB-40	65
Minor Arterial	SU	65
Collector	SU	55
Local Road
Paved	S-BUS36	45
Gravel	S-BUS36	35
Urban
Interstate / Freeway Ramp Terminal	WB-50	65
Ramp
Free-Flow	WB-50 / WB-65*	35 (minimum)**
Entrance / Exit	WB-50 / WB-65*	35 (minimum)**
Loop	WB-50 / WB-40	35(minimum)**
Primary Arterial	WB-50 or WB-40	55
Minor Arterial	WB-40 or BUS-40	45
Collector	BUS-40 or SU	35
Residential / Local Road	SU or P	35
*WB-65 recommended for facilities that provide access to freight terminals and other commercial truck facilities ** Refer to Section 3.3.3 Freeway Ramps. Design Vehicle Type Symbols:  BUS=Intercity Bus/Motor Coach, P=Passenger Car, S-BUS=School Bus, SU=Single-Unit Truck, WB=Semi Trailer