User: Please write a summary of the kinds of vehicles that are used for ambulances.

Context:
Vehicle types
In North America (US and Canada), there are four types of ambulances. There are Type I, Type II, Type III, and Type IV. Type I is based upon a heavy truck chassis-cab with a custom rear compartment that is often referred to as a "box" or "module." Type I ambulances are primarily used for Advanced Life Support (ALS), also referred to as Mobile Intensive Care Unit (MICU) in some jurisdictions, and rescue work. A Type II ambulance is based on a commercial heavy-duty van with few modifications except for a raised roof and a secondary air conditioning unit for the rear of the vehicle. These types of ambulances are primarily used for Basic Life Support (BLS) and transfer of patients but it is not uncommon to find them used for advanced life support and rescue. Type III is a van chassis-cab but with a custom-made rear compartment and has the same uses as Type I ambulances. Type IV is for smaller ad hoc patient transfer that use smaller utility vehicles in which passenger vehicles and trucks would have difficulty in traversing, such as large industrial complexes, commercial venues, and special events with large crowds; they generally do not fall under Federal Regulations.

Ambulances can be based on many types of vehicle although emergency and disaster conditions may lead to other vehicles serving as makeshift ambulances:

A modern American ambulance built on the chassis of a Ford F-450 truck, with extensive external storage

Many modern Canadian and European ambulances are built on the Mercedes-Benz Sprinter chassis. Some, like this Niagara Region example, use custom rear compartments.
Van or pickup truck – A typical general-purpose ambulance is based on either the chassis of a van (vanbulance) or a light-duty truck. This chassis is then modified to the designs and specifications of the purchaser. Vans may either retain their original body and be upfitted inside, or may be based on a chassis without the original body with a modular box body fitted instead. Those based on pickup trucks almost always have modular bodies. Those vehicles intended for especially intensive care or require a large amount of equipment to be carried may be based on medium-duty trucks.
Car – Used either as a fly-car for rapid response or to transport patients who can sit, these are standard car models adapted to the requirements of the service using them. Some cars are capable of taking a stretcher with a recumbent patient, but this often requires the removal of the front passenger seat, or the use of a particularly long car. This was often the case with early ambulances, which were converted (or even serving) hearses, as these were some of the few vehicles able to accept a human body in a supine position. Some operators use modular-body transport ambulances based on the chassis of a minivan and station wagon.
Motorcycle and motor scooter – In urban areas, these may be used for rapid response in an emergency as they can travel through heavy traffic much faster than a car or van. Trailers or sidecars can make these patient transporting units. See also motorcycle ambulance.

Patient being loaded into a medical helicopter
Bicycle – Used for response, but usually in pedestrian-only areas where large vehicles find access difficult. Like the motorcycle ambulance, a bicycle may be connected to a trailer for patient transport, most often in the developing world. See also cycle responder.
All-terrain vehicle (ATV) – for example quad bikes; these are used for response off-road, especially at events. ATVs can be modified to carry a stretcher, and are used for tasks such as mountain rescue in inaccessible areas.

Golf Cart converted into an ambulance
Golf cart or Neighborhood Electric Vehicle – Used for rapid response at events or on campuses. These function similarly to ATVs, with less rough terrain capability, but with less noise.
Helicopter – Usually used for emergency care, either in places inaccessible by road, or in areas where speed is of the essence, as they are able to travel significantly faster than a road ambulance. Helicopter and fixed-wing ambulances are discussed in greater detail at air ambulance.
Fixed-wing aircraft – These can be used for either acute emergency care in remote areas (such as in Australia, with the 'Flying Doctors'), for patient transport over long distances (e.g. a re-patriation following an illness or injury in a foreign country), or transportation between distant hospitals. Helicopter and fixed-wing ambulances are discussed in greater detail at air ambulance.
Boat – Boats can be used to serve as ambulances, especially in island areas or in areas with a large number of canals, such as the Venetian water ambulances. Some lifeboats or lifeguard vessels may fit the description of an ambulance as they are used to transport a casualty.
Bus – In some cases, buses can be used for multiple casualty transport, either for the purposes of taking patients on journeys, in the context of major incidents, or to deal with specific problems such as drunken patients in town centres. Ambulance buses are discussed at greater length in their own article.
Trailer – In some instances a trailer, which can be towed behind a self-propelled vehicle can be used. This permits flexibility in areas with minimal access to vehicles, such as on small islands.
Horse and cart – Especially in developing world areas, more traditional methods of transport include transport such as horse and cart, used in much the same way as motorcycle or bicycle stretcher units to transport to a local clinic.
Fire engine – Fire services (especially in North America) often train firefighters to respond to medical emergencies and most apparatuses carry at least basic medical supplies. By design, most apparatuses cannot transport patients unless they can sit in the cab.
Assistant: The most common types of vehicle used as an ambulance are cars, vans or pickup trucks. Depending on many factors, such as accessibility to the patient and/or medical services or the urgency of treatment, other types of vehicles are used as well, including: bicycles, all-terrain vehicles, golf carts, helicopters, fixed-wing aircraft, boats, busses, trailers, horse and cart, and fire engines.