There are many different kinds of bicycle trailers available on the market today, they can be divided into two main categories determined by end use. These two are trailers to carry people and trailers to carry cargo.
Trailers to carry people can be divided into three categories: Single child trailers, double child trailers, and adult trailers.
Single bike trailers are typically 4 or 5 inches narrower than double trailers. They are easier to maneuver when used as strollers and do not present as large a presence on sidewalks compared to double strollers. They are slightly more prone to tipping over when riding to fast due to their narrower wheelbase. Many transit systems do not allow double strollers to ride on buses and this is usually not the case for single strollers. If you live in a tight urban space, only intend to carry one child, and use public transit then you should consider a single bike trailer. Upgrades might be available to convert you trailer to a stroller or jogger.
Double child trailers are much more popular than single child trailers. Most double trailers can position one child in the center if riding alone. Some brands fold faster than others, some models have suspension, and some have durable plastic floors.
Adult bicycle trailers accommodate taller people and are heavier built than regular child trailers. They require greater distance to stop and more care when riding your bicycle.
Trailers to carry cargo vary according to end use and capacity: Grocery getters, pet trailers, boat trailers, work trailers, golf trailers, and vending bike trailers.
Grocery trailers help households operate in a urban environment without a car. The capacity is usually about 75-100 lbs which is suitable for weekly trips to the supermarket or farmer market. Some cargo bike trailers easily convert to a shopping carts so you can take them into the supermarket. A typical grocery getter will carry the load of 4-6 panniers. They are usually easier to load than panniers
Pet trailers differ from child trailers in that their wheels are more in the center of the base platform. They do not have seats and the floor is usually padded. Some pet trailers simply accommodate a kennel on a base frame.
Boat trailers are single purpose bicycle trailers because of the unique shape of boats. Boat trailers are a great benefit to people who live close enough to the water to cycle but too far to walk with a boat. Parking a bicycle by the water is not an issue however parking a car can be difficult and expensive.
Work trailers are meant to carry tools for a specific trade. The most common are landscaping trailers to carry a mower and a few garden tools. In a dense urban environment the ability to park a pickup truck with a trailer is impossible on a narrow residential street and is also not appreciated by the neighbours. Work trailers are also used by painters, musicians, physiotherapists, dog groomers, and veterinarians to name a few.
Golf trailers are used when the course is too far away to walk to and moving the clubs in and out of the trunk of your car is a hassle.
Vending bike trailers are used for craft or food sellers. The trailers can be insulated and can have display cases for jewelry or crafts