Why the sudden interest in the classification of bikes?
The AASHTO Green Book (ref. 831) says that:
Key controls in geometric highway design are the physical characteristics and the proportions of vehicles of various sizes using the highway.
“the bicycle should also be considered as a design vehicle where bicycle use is allowed on a highway”
The Los Angeles bicycle plan, technical design handbook (ref. 917) has this to say on the subject:
Similar to motor vehicles, bicyclists and their bicycles come in a variety of sizes and configurations. This variation can take the form of a conventional bicycle, a recumbent bicycle, a tricycle, or the behavioral characteristics and comfort level of the bicyclist riding the device. Any bikeway undergoing design should consider the various types of bicycles that may be expected on the facility and design with that set of critical dimensions in mind.
Whilst a UK document on cycle infrastructure design (ref. 745) says:
… there is a great variety of types (of bicycle) in use. Designers should anticipate the use of nonstandard cycles, particularly in areas with high levels of utility cycling, on recreation routes and on routes serving schools and nurseries. Designing to accommodate tandems, tricycles and trailers opens up cycle routes to families with children and users of handcranked cycles.
The argument is then that, to design roads for bikes an engineer needs to know the size of bikes, and that the size of bikes varies with the type (or class). For example, a standard bicycle may be 1.78m long, but a bicycle with child trailer can be 3.05m long (see table 1).
Can bikes be larger than cars?
It can be a mistake to think that bikes are smaller than cars. For example, the length of a bicycle with child trailer may be 3.05m, but the length of Toyota’s iQ is only 2.985m. Table 2 compares the dimensions of a VW Golf car with different types of bike. It shows that bikes can be longer and higher than cars.
Driver eye height
Sight distance is one of the important parameters used in highway design. It is dependent (amongst other things) on the height of the driver’s eye above the road surface. The higher the driver eye height is, the better is his sight distance. Table 3 shows that whilst the eye height of a bicyclist on a standard bike is higher than the recommended figure for a car driver, the eye height of a recumbent bicyclist is lower – and for the rider of a velomobile, it can be quite a bit lower (a velomobile is the bike world equivalent of a sports car).
Another way to classify bikes – by function
The AASHTO reference establishes “four general classes of design vehicles”: (1) passenger cars, (2) buses, (3) trucks, and (4) recreational vehicles. It then gives dimensions for 20 design vehicles within these general classes. One German reference(ref. 622) gives dimensions for 4 classes of vehicle (private cars, lorries, buses and refuse vehicles) with a total of 13 design vehicles for these classes. These two references classify motor vehicles by function (buses, goods vehicles etc). Perhaps bikes can also be classified by function.
622 – Germany, Bemessungsfahrzeuge und Schleppkurven zur Überprüfung der Befahrbarkeit von Verkehrsflächen; fgsv (2001)
745 – UK, Local transport note 2/08 “Cycle infrastructure design”, DTp (2008)
831 – USA, AASHTO, A policy on the geometric design of highways and streets (2011)
917 – USA, Los Angeles 2010 Bicycle Plan, technical design handbook, USA (2011)